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Microfiche 

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Collection  de 
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Canadian  Instituta  for  Hiatorical  Microraproductiont  /  Inttitut  Canadian  da  microraproductiona  hiatoriquaa 


Technical  and  Bibliographic  Notes/Notes  techniques  et  bibliographiques 


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D 
D 


D 


Coloured  covers/ 
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I      I   Covers  damaged/ 


Couverture  endommagde 

Covers  restored  and/or  laminated/ 
Couverture  restaurte  et/ou  pellicuMe 

Cover  title  missing/ 

Le  titre  de  couverture  manque 

Coloured  maps/ 

Cartes  gAographiques  en  couleur 


I      I   Coloured  Ink  (i.e.  other  than  blue  or  black)/ 


D 


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Coloured  plates  and/or  illustrations/ 
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L'Institut  a  microfiimA  le  meiileur  exemplaire 
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sont  indiqu^s  ci-dessous. 


D 
D 

n 

D 
D 


D 


Coloured  pages/ 
Pages  de  couleur 

Pages  damaged/ 
Pages  endommag^es 

Pages  restored  and/or  laminated/ 
Pages  restaur6es  et/ou  pelliculAes 

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Pages  detached/ 
Pages  d6tach6es 


I     I   Showthrough/ 


Transparence 

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Quaiit^  inAgale  de  I'lmpression 

Includes  supplementary  materif 
Comprend  du  materiel  supplAmentaIre 

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This  item  is  filmed  at  the  reduction  ratio  checked  below/ 

Ce  document  est  film*  au  taux  de  reduction  IndiquA  ci-dessous. 

10X  14X  18X  ax 


12X 


16X 


aox 


^ 


2ex 


»x 


28X 


32X 


The  copy  filmed  here  has  been  reproduced  thanks 
to  the  generosity  of: 

Library  of  Congress 
Photoduplication  Service 


L'exemplaire  filmA  fut  reproduit  grftce  A  la 
gAnArositA  de: 

Library  of  Congress 
Photoduplication  Service 


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possible  considering  the  condition  and  legibility 
of  the  original  copy  and  In  keeping  with  the 
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beginning  with  the  front  cover  and  ending  on 
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or  illustrated  impression. 


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plus  grand  soin,  compte  tenu  de  la  condition  et 
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conformity  avec  les  conditions  du  contrat  de 
filmage. 

Les  exemplalres  orlglnaux  dont  la  couverture  en 
papier  est  ImprimAe  sont  filmte  en  commengant 
par  le  premier  plat  et  en  terminant  soit  par  la 
dernlAre  page  qui  comporte  une  empreinte 
d'Impression  ou  d'lllustratlon,  soit  par  le  second 
plat,  salon  le  cas.  Tous  les  autres  exemplalres 
orlglnaux  sont  filmto  en  commenpant  par  la 
premiere  page  qui  comporte  une  empreinte 
d'Impression  ou  d'lllustratlon  et  en  terminant  par 
la  dernlAre  page  qui  comporte  une  telle 
empreinte. 


The  last  recorded  frame  on  each  microfiche 
shall  contain  the  symbol  ^*»  (meaning  "CON- 
TINUED"), or  the  symbol  y  (meaning  "END"), 
whichever  applies. 


Un  dee  symboles  suivants  apparaftra  sur  la 
dernlAre  image  de  cheque  microfiche,  selon  le 
cas:  le  symbols  -^  signifie  "A  SUIVRE",  le 
symbols  V  signifie  "FIN". 


Maps,  plates,  charts,  etc.,  may  be  filmed  at 
different  reduction  ratios.  Those  too  large  to  be 
entirely  included  in  one  exposure  are  filmed 
beginning  in  the  upper  left  hand  corner,  left  to 
right  and  top  to  bottom,  as  many  frames  as 
required.  The  following  diagrams  illustrate  the 
method: 


Les  cartes,  planches,  tableaux,  etc.,  peuvent  Atre 
filmte  A  dee  taux  de  reduction  diff Arents. 
Lorsque  le  document  est  trop  grand  pour  Atre 
reproduit  en  un  seul  clichA,  il  est  filmA  A  partir 
de  Tangle  supirieur  gauche,  de  gauche  A  droite, 
et  de  haut  en  bas,  en  prenant  le  nombre 
d'Images  nAcessaire.  Les  diagrammes  suivants 
illustrent  la  mAthode. 


1 

2 

3 

32X 


1 

2 

3 

4 

5 

6 

llHMrr,|l>HB| 


■MN-MHMMMWIlHI 


A  TEXT-BOOK  OF 


ANIMAL  PHYSIOLOGY 


WITH  INTRODUCJTORY  CHAPTERS 
.    ON  GENERAL  BIOLOGY 
AND  A  FULL  TREATMENT  OF  REPRODUCTION 


FOR  STUDENTS  OF  HUMAN  AND  COMPARATIVE  (VETERINARY) 
MEDICINE  AND  OF  GENERAL  BIOLOGY 


m 


WESLEY    MILLS 

■.  A.,  M.  D.,  h.  R.  C'k  (EXQ.) 


nwMMsoK  OF  nmiouwT  m  mo  «ll  vNivimnT  and  thb  TinmNART  columb 

■OHTMBAL 


WITH  OVKR  FIVB  HUNDRED  ILLUSTRATIONS 


YORK 
D.  APPLETON    AND    COMPANY 

tAMDOir:  OAXTOR  BOUSR,  rATnUTOnRK  S^UARI 

1869 


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1 

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Comuavt,  IHP, 

Bt  d.  appletov  and  company. 


9,0  the  memors  of 


ROBERT  PALMER  HOWARD,  M.  D.,  LL.  D., 

I^n  BBAK  AMD  FMOnMM*  OT  aBDIOIIIB  III  MCaiU.  VMlrMMTT, 

WHOSE  TBACBIMO  AMD  PSACTIOK  BVKB  TBITDBD  TOWARDS 

THE  SEOOGXltlOM  Or  THE  IMFOkTAKCB  OF  PBTSIOLOOT  TO  XEDICINB, 

AND  WHOSE  UFE  ILLV8THATED 

WHAT  18  bOrrV  AND  NOBLE  IN  HUMAN  EXI8TBMCB, 

TBn  WOBX  IS  DBDIOATID 
XM  BBVBRBNCE   AND  ORATITVDB. 


,t  <!)^^$fmmmmmmmmtmiiiMWKm0'i^ 


Ikia 


IHiHHHHHHI 


mam 


PREFACE. 


The  comparative  method,  the  introduction  of  the  teach* 
ings  of  embryology  and  of  the  welding  principles  of  evolution 
as  {Mtrt  of  the  essential  structure  of  zoology,  may  be  said  to 
have  completely  revolutionized  that  science;  and  there  is 
scarcely  a  text-book  treating  of  the  subject,  however  element- 
ary, which  has  not  been  molded  in  accordance  with  these 
guiding  lines  of  thought.  So  far  as  I  am  aware,  this  can 
not  be  said  of  a  single  book  on  the  subject  of  physiology. 
Feeling,  therefore,  that  the  time  had  come  for  the  appearance 
of  a  work  which  should  attempt  to  do,  in  some  degree  at 
least,  for  physiology  what  has  been  so  well  done  for  morphol- 
ogy, the  present  task  was  undertaken.  But  there  were  other 
changes  which  it  seemed  desirable  to  make.  I  think  any  one 
who  will  examine  the  methods  and  reasoning  of  the  physi- 
ology of  the  day  will  not  fail,  on  close  scrutiny,  to  recognize 
a  tendency  to  speak  of  certain  conclusions,  for  various  organs 
(and  functions),  as  though  they  applied  to  these  organs  in 
whatever  group  of  animals  found,  or,  at  all  events,  for  man, 
no  matter  what  the  species  of  the  animal  that  had  been  ex- 
perimented upon.  For  some  years  I  have,  in  publications  of 
my  own  original  researches,  strongly  protested  gainst  such 
methods  as  illogical.  I  am  wholly  at  a  loss  to  understand 
how  a  work,  built  upon  the  most  fragmentary  and  hetero- 
geneous evidence,  derived  from  experiments  on  a  few  groups 
of  animals,  or  a  certain  amount  of  human  clinical  or  patho- 
logical evidence,  can  be  fittingly  termed  a  treatise  on  "  human 
physiology."    It  will  scarcely  be  denied  that  conclusions  such 


-i^&mMki^:^:-'  ■■  h.i&l,  "'.^4i-K.m  " WMI' 


r 


VI 


ANIMAL  PHYSIOLOGY. 


as  this  method  implies  would  not  be  tolerated  in  the  subject 
of  morphology. 

While  in  the  present  work  what  is  strictly  applicable  to 
other  animals  and  to  man  has  not  always  been  kept  apart, 
an  effort  has  been  made  throughout  to  be  cautious  in  all  the 
conclusions  drawn — a  state  of  mind  warranted  by  the  past 
history  and  the  present  tendencies  of  physiology.  Until  our 
laboratory  methods  become  more  perfected,  the  comjwrative 
method  more  extensively  applied,  and  conclusions  drawn  from 
"experiments"  modified  by  comparison  with  the  results  of. 
clinical,  pathological,  and  all  other  available  sources  of  infor- 
mation, I  feel  convinced  that  we  are  called  upon  to  teach 
cautiously  and  modestly. 

Treating,  as  we  do  in  our  books,  each  subject  in  a  separate 
chapter,  there  is,  as  I  know  by  observation,  the  greatest  danger 
that  the  student  may  get  the  idea  that  each  function  of  the 
body  is  discharged  very  much  independently;  accordingly, 
there  has  been  throughout  a  most  persistent  effort  made  to 
impress  the  necessity  for  ever  remembering  the  absolute  de- 
pendence of  all  parts.  Unless  this  be  thoroughly  infused 
into  a  student,  it  is  impossible  that  he  can  ever  understand 
the  wide  world  of  natural  objects,  or  the  narrower  one  of  un- 
natural (in  a  sense)  organisms,  as  seen  in  the  hospital  ward. 

Recognizing  how  important  it  is  to  teach  the  young  stu- 
dent to  become  an  observer  and  an  investigator  in  spirit  and 
in  some  degree  in  fact,  only  such  treatment  of  elaborate 
methods  has  been  introduced  as  will  enable  him  to  form  a 
general  acquaintance  with  the  modes  iu  which  laboratory 
work  is  earned  on,  while  simple  ways  of  verifying  the  essen- 
tial truths  of  physiology  have  been  constantly  brought  before 
him.  As  to  how  far  these  are  actually  carried  out  will  de- 
pend not  a  little  on  the  teacher.  The  student  who  learns  thus 
to  observe  and  to  verify  will  not  fail  to  apply  the  method  in 
his  future  career,  whatever  that  may  be — ^whether  medical  or 
othdr-— nor  is  he  so  likely  to  throw  his  physiology  overboard , 
as  a  useless  cargo  as  soon  as  his  primary  examination  has 
been  passed. 


PREFACE. 


▼ii 


By  frequently  calling  attention,  as  has  been  done  through- 
out, to  actually  discovered  or  possible  differences  in  function 
for  different  groups  of  animals,  it  is  believed  that  the  student 
will  become  possessed  of  a  spirit  of  caution  in  drawing  con- 
clusions that  will  fit  him  the  better  for  the  hospital  ward  in 
another  respect,  viz.,  that  he  will  be  prepared  for  those  indi- 
vidual differences  actually  existing,  and  which  t:eem  to  have 
been  largely  ignored  in  so  many  works  on  physiology,  with 
the  natural  consequence  that  the  student,  not  finding  his 
physiology  squaring  with  the  facts  of  the  clinique,  and  not 
being  prepared  for  the  situation,  the  result  is  disappointment 
and  disgust,  instead  of  the  actual  continuation  of  the  study, 
especially  as  human  physiology. 

With  a  view  of  widening  the  student's  field  of  vision,  sec- 
tions, under  the  heading  "  Special  Considerations,"  have  been 
introduced,  which  it  is  hoped  will  not  fail  to  interest  and 
stimulate. 

Most  teachers  of  experience  will  welcome  the  summary 
with  which  each  chapter  concludes.  In  connection  with  no 
subject  perhaps  can  the  art  of  generalizing  be  better  taught 
than  with  physiology,  and  to  this  end  these  brief  synoptical 
sections  will,  it  is  thought,  prove  helpful. 

Systematic  instruction  in  either  macroscopic  or  microscopic 
anatomy  has  not  been  undertaken — ^in  fact,  can  not  be  at- 
tempted, it  is  believed,  except  at  the  expense  of  physiology 
proper— in  a  work  of  moderate  compass.  At  the  same  time 
attention  has  been  called  to  those  points  which  have  a  special 
bearing  on  each  function,  and  a  number  of  illustrations  have 
been  inserted  with  this  object  in  view. 

The  introduction  of  the  subject  of  defelopment  at  so  early 
a  stage  is  a  departure  that  calls  for  a  word  of  explanation. 
An  attempt  has  been  made  to  use  embryological  facts  to 
throw  light  upon  the  different  functions  of  the  body,  and 
especially  their  relations  and  interdependence.  It  therefore 
became  necessary  to  treat  the  subject  early.  It  is  expected, 
however,  that  the  student  will  return  to  it  after  reading  the 
remaining  chapters  of  the  work. 


I  I  llliiUjjg 


vili 


ANIMAL  PHYSIOLOGY. 


As  BO  large  a  proportion  of  those  who  enter  upon  the 
study  of  medicine  begin  their  career  without  any  adequate 
preparation  in  general  biology,  the  subjept,  as  presented  in 
this  work,  will,  let  me  hope,  meet  an  actual  need,  and  prove 
helpful  in  attaining  a  broad  and  sound  view  of  the  special 
doctrines  of  biology. 

It  is  scarcely  necessary  to  iiimark  that  clinical  and  path- 
ological facts  have  not  been  introduced  with  the  view  of 
teaching  either  clinical  medicine  or  pathology,  but  to  indi- 
cate to  the  student  how  his  physiology  bears  on  his  profes- 
sion, and  how  the  above-mentioned  subjects  throw  light  upon 
physiology  proper  and  lend  interest  to  that  subject. 

My  aim  has  be  ti  to  make  the  book,  from  first  to  last, 
educative;  and,  retaining  a  vivid  recollection  of  the  severe 
strain  put  upon  the  memory  of  the  medical  student  by  our 
present  method  of  crowding  bo  much  into  at  most  four  years 
of  study,  an  attempt  has  been  made  to  avoid  overloading  the 
book  with  mer«  facts  or  technical  details,  as  well  as  to  pre- 
sent the  whole  subject  in  as  succinct  a  form  as  is  compatible 
with  clearness.  Recognizing,  too,  the  very  shifting  character 
of  physiological  theories,  the  latter  have  generally  been  pretty 
well  kept  apart  from  the  actual  facts. 

It  is  hoped  that  the  abundance  of  the  illustrations  will 
prove  more  acceptable  than  would  lengthy  treatment  of  sub- 
jects in  the  text,  for,  if  the  matter  of  a  book  is  to  be  digested 
and  assimilated,  either  by  the  student  of  general  biology  or 
by  the  hard-worked  medical  student,  it  must  not  be  bulky. 

The  illustrations  have  been  chosen  from  the  best  available 
sources,  and  the  authorship  of  each  one  duly  acknowledged 
in  the  body  of  the  work.  Several  original  diagrams,  such  as 
I  find  exceedingly  useful  in  my  own  lectures,  have  been  in- 
troduced. 

This  book  is  really  an  embodiment  of  my  own  course  of 
lectures,  as  given  during  the  past  two  years  more  especially, 
and  with  the  highest  satisfaction,  I  think  it  may  be  said,  to 
both  students  and  teacher. 

I  have  unbounded  confidence  in  the  plan  of  the  wprk,  and 


iWiSJ 


PREFACE. 


IX 


I  trust  that  its  newness  may  excuse,  to  some  degree,  any 
shortcomings  in  the  execution.  Such  a  book  has  become  a 
necessity  to  myself,  and  it  is  hoped  will  be  welcomed  by 
others.  I  trust  the  work  may  prove  suitable,  not  only  for 
the  student  of  human  medicine,  but  for  the  increasing  num- 
ber of  students  of  comparative  or  veterinary  medicine,  who 
may  desire  a  broad  basis  for  the  study  of  disease  in  the 
various  animals  they  are  called  upon  to  treat.  I  have  en- 
deavored to  make  the  work  specially  acceptable  to  the  stu- 
dent of  general  biology. 

It  only  remains  for  me  to  crave  the  indulgence  of  all 
readers,  and  to  thank  my  publishers,  Messrs.  D.  Appleton  & 
Co.,  for  their  uniform  courtesy  and  the  great  pains  they  have 
taken  to  present  the  work  in  worthy  form. 

Wkslky  Mills. 

PBYBioiioeicAL  Laboratory,  McGill  University, 
MoNTRKAi.,  September,  1889. 


m^'i'Si'iTlK' 


I  irmlMi'iUfl 


I 


CONTENTS. 


I 


OlMlkAL  BlOtOGT 

Introduction  . 

Tabular  statement  of  the  Bubdivisions  of  Biology 
ThrCbll  . 

Aninul  and  vegetable  cells 

Structure  of  cells  . 

Cell-contents  . 

The  nucleus    . 

Tissues   . 

Summary 
Uniceixulab  OBOAinsilS 


Tl. 


(VniKTABLB) 


Teast. 
Morphological 
Chemical 
Physiological  . 
Conclusions 
S.  ProtocooouB 
Morphological 
Physiological  . 
Conclusions    . 
UnCRLLUIiAB  Akimaui 
The  proteoa  animalcule 
Morphological 
Physiological  . 
Conclusions    . 
pABAsmc  Okoamibms 
Fungi 

Muoor  mucedo 
The  Bacteria  . 
UxicBU.ui.AB  Animals  wrra  Dipfbbbiitiatiom  or 


The  ball-animalcule 
Structure 
Fanottons 

MuLTIOBLLVLAU  OBOANMMS 

The  fewh-WBter  polyps . 
T«B  Cbll  bboomudbbbd 
Tn  Akimal  Body-hui  epitomiied  account  of  the  functions  of  a  mammal 


Stbuotvbb 


PA«B 

1 

1 

4 

S 

S 

5 

7 

7 

8 

8 

9 

9 

9 

10 

10 

10 

11 

11 

11 

IS 

18 

IS 

IS 

IS 

14 

15 

15 

15 

18 

90 

SO 

SO 

SI 

S8 

S8 

98 

97 


I 


zu 


ANIMAL  PHYSIOLOGY. 


Nature — Explanfttions 


and 


illu»- 


LiTiNO  AMD  LivELESs  Mattee— General  explanation  and  comparison  of 

their  properties 

Classification  or  the  Animal  Kinodom 
Tabular  statement 
Man's  place  in  the  animal  kingdom 
The  Law  of  Periodicity  or  Rhythm  in 

trations 

The  Law  of  HABrr.       .       . 
Its  foundation       .  .       . 

Instincts 

The  Orioin  op  the  Forms  of  Life 
Arguments  from : 

Morphology  .... 
Embryology  .... 
Mimicry  .  .       . 

Rudimentary  organs 
Geographical  distribution 
Paleontology  .... 
Fossil  and  existing  species     . 
Progression  .    '   . 

Domesticated  animals 

Summary 

Beprodvctiom 

General 

TheoTum    , 

The  origin  and  development  of  the 
Changes  in  the  ovum  itself    . 
The  male  cell        .... 
The  origin  of  the  spermatozoon 
Fertilisation  of  the  oTum 
Segmentation  and  subsequent  changes 
The  gastrula  . 
The  hen's  egg .... 
The  origin  of  the  fowl's  egg  . 
Embryonic  membranes  of  birds    . 
The  foetal  (embryonic)  membranes  of 
The  placenta  .... 
The  disooidal  placenta   . 
The  metadisooidal  placenta    . 
The  lonary  placenta 
The  diffuse  placenta 
The  polycotyledonary  placenta 
'      Mioroaoopic  structure  of  the  placenta 
Illustrations    .... 
Evolution       .... 
Summary       .... 
Tbi  Dbtelopmimt  or  thi  Embryo  Itsbut 
Oerm-layen    .  .       < 

Origin  of  the  vaaouhur  system 
The  growth  of  the  emlwyo    . 


oTum 


mammals 


PAOB 

31 
33 
85 
85 


40 
40 
41 
41 

48 

48 

48 

48 

45 

45 

45 

46 

46 

47 

50 

50 

M 

57 

50 

60 

61 

68 

68 

66 

67 

68 

7S 

76 

80 

81 

81 

80 

86 

86 

87* 

87 

80 

80 

90 

M 

•7 

101 


&im 


t 


PAOI 

31 
88 
85 
85 


40 
40 
41 
41 

48 
48 
48 
48 
48 
45 
45 
40 
48 
47 
50 
50 
M 
57 
50 
00 
01 
08 
88 
08 
07 
OB 

n 

70 
80 
81 
81 
80 
80 
80 
87' 
87 
80 
80 
00 
OS 
07 
101 


CONTENTS.  xiii 

DErELOPMENT  OF  THE  VaBCUI^R  SySTEM   IN   VeRTEBBATES  .           .          .           .  108 

The  later  stages  of  the  foetal  circulation 108 

Detelopxent  or  the  UROOEinTAi.  System 108 

A  as  Physioumiicai.  Aspects  of  Dktelopiiemt 112 

Menstruation  and  ovulation 113 

The  nutrition  of  the  ovum 115 

The  foetal  circulation             ...       . HO 

Parturition 120 

Changes  in  the  circulation  at  birth       .       .       .       ...       .       .       .  120 

Sexual  coitus 121 

Oroanic  Evolution  reconsidered 127 

Different  theories  criticised — new  views 127 

The  Chemical  Constitution  or  the  Animal  Body 185 

Proximate  principles 187 

General  characters  of  proteids .  138 

Certain  non-crystalline  bodies 138 

The  fats.       . 180 

Peculiar  fats 140 

Carbohydrates        .       .       .       .        .       .        .       .       .       .       •        •  *** 

Nitrogenous  metabolites 140 

Non-nitrogenous  metabolites 141 

PhtsiolooicaIi  Brsrabch  and  Physiolooical  Rbasoninq  .              .      '.  141 

The  Blood 147 

Comparative   .       .       .    • •       •       .148 

Corpuscles 140 

History  of  the  blood-cells 151 

Chemical  composition  of  the  blood        .       •       •    '  •       •       «       •'  154 

Composition  of  serum 155 

Composition  of  the  corpuscles 155 

The  quantity  and  dbtribution  of  the  blood 150 

The  coagulation  of  the  blood .       •       .137 

Clinical  and  pathol«gi(»l ^03 

Summary 106 

The  Contractili  Tissuia 100 

General    . 100 

Comparative 107 

Ciliary  movements 108 

The  irritability  of  muscle  and  nerve 100 

Applications  of  the  Orapbio  Mbthod  so  thr  Study  or  Mubcu 

Physiology. .-     .              .       .  171 

Chronographs  and  various  kinds  of  i^pantus      ....    171-174 

A  single  muscular  oontraotion      .       .       .       '. 178 

Tetanic  oontTRictfon 108 

The  musole-tone            184 

The  strength  of  the  stimulus 185 

The  changes  in  A  muscle  during  oontraotion 188 

The  elasticity  of  muscle 187 

The  electrical  phenomena  of  miuola      .......  186 

Chemical  changes  In  muscle .       .       .108 

ThMmwl  change*  in  the  contracting  BMWole 105 


.«- '•**-<«MiM|.!»#NMP9*'M 


j 


xiv 


ANIMAL  PHYSIOLOGY. 


The 


The 


The  physiology  of  nerre 
ElectrotonuB   . 
Pathological  and  clinical 
Law  of  contraction . 
Electrical  organs    . 
Muscular  work 

Circumstances  influencing  the  character  of  muscular 
The  influence  of  blood-supply  uid  fatigue    . 
Separation  of  muscle  from  the  central  nervous  system 
The  influence  of  temperature 
The  intimate  nature  of  muscular  and  nervous  action 
Unstriped  muscle  . 

General    .... 
Comparative   . 
Special  considerations    . 
Functional  variations     . 
Summary  of  the  physiology  of  muscle  and  nerve 
Nervous  System— Gehebal  Considebatioms 
Experimental  . 
Automatism    . 
Conclusions    . 
Nervous  inhibition . 
Circulation  or  thi  Bux>d 
General    .... 
The  mammalian  heart    . 
Circulation  in  the  mammal   . 
The  action  of  the  liiammalian  heart 
The  velocity  of  the  blood  and  blood-pressure 

Gtoneral 

Comparative    . 
The  circulation  under  the  microscope  . 
The  characten  of  the  blood-flow  . 
Blood-pressure  •       •    • 

The  Heart 
The  cardiac  movements 
The  impulse  of  the  heMrt 
Investigation  of  the  heart-beat  from  within 
The  cardiac  sounds        .... 
Causes  of  the  sounds 

Bndo-oardiao  pressuns 

The  work  of  tiie  heart  . 
Variations  in  the  cardiac  pnlntion 

The  pulse 

Features  of  an  arterial  poise-tracing 
Venous  pulse  .       .       .       •       • 
Pathologiotl   •  •       • 

Comparative 

The  beat  of  {he  heart  and  its  modifications 
The  nervous  system  in  relation  to  the  heart 
Influence  of  the  vagus  nerve  on  the  iMart    , 


i.mtmmmmmmtmiii''i'^-'' 


CONTBNT& 


XV 


vity 


227 


Conolurions 

Tbe  accelerator  nerves  of  the  heart 

Human  phyfiology .... 
The  heart  in  reUtion  to  Mood-pressare 

The  inflaenoe  of  the  c  uantity  of  blood 

Condnaions 

The  capillaries 

Special  considerations  .... 

Pathological  ..... 

Personal  obsenrations 

ComparatiTe 

Evolution 

Summary  of  the  physiology  of  the  cirouUtion 
DiewTioir  op  Food  .... 

Foodstnih,  milk,  etc 

Bmtoyologioal 

Comparative  . 
The  digestive  juices 

Saliva  and  its  action 

Secretion  of  the  different  glands 

Comparative    . 

Pathologioai    . 

Ghutrie  juice  . 
Bile 

General   . 

Pigments 

Digestive  action 

Comparative  . 
Pancreatic  secretion 
Snocus  enteriens    . 

Comparative  . 
Secntion  aa  a  physiological  process 

Secretion  of  the  salivary  glands 

Secretion  by  the  stomadi 

The  secretioa  of  Ule  and  panoteatic  jnioe 
The  nature  of  the  act  at  secretion . 

Self-digestion  of  the  digestive  wgans 

Comparative  . 
The  movements  of  the  digestive  organs 

Deglutition 

Comparative   .       . 

The  movements  of  the  9tomaoh 

Comparative 

Pkthologioal 

The  intevtinal  movements      « 

Defecation 

Vomiting 

Comparative 

Plkthologioal 

The  nmoval  of  digestive  prodoots  from  the  alimentuy 


260 
270 
278 
274 
275 
277 
281 


286 
290 
290 
29S 
296 
806 
806 
807 
808 
806 
808 
811 
811 
812 
818 
814 
814 
817 
810 
819 
819 
898 
828 
886 
829 
880 


888 
886 
881 

887 
887 


889 

841 


•«*«s^' 


iiiHlll,MWH'IIWHl'WW'*!ll"'lil 


XVI 


ANIMAL  PHYSIOLOGY. 


in  the  alimentary  canal 


Lymph  and  chyle 

The  movements  o£  the  lymph— comparative 
Pathological    . 
Faeces      .... 
Pathological    . 
The  changes  produced  in  the  food 
General    .... 
Comparative    . 
Pathological    . 
Special  considerations   . 
Various   .... 
Human  physiology 
Evolution 
Summary 
Trb  Respiratory  Ststkm 

General  .        .        .       • 
Anatomical     . 
The  entrance  and  exit  of  air . 
The  muscles  of  respiration 
Types  of  respiration 
Personal  observation 
Comparative  .... 
The  quantity  of  air  respired  . 
The  respiratory  rhythm 
General   .       .       .       • 
Pathological    . 
Respiratory  sounds. 
Comparison  of  the  inspired  and  the  expired  air 
Respiration  in  the  blood 
Hemoglobin  and  its  derivatives 
General   .... 
Blood-spectra  . 
Comparative    . 

The  nitrogen  and  the  carbon  dioxide  of  the 
Foreign  gases  and  respiration 
Respiration  in  the  tissues     .... 
The  nervous  system  in  relation  to  respiration 
Nerves  and  centers  concerned 
The  influence  of  the  condition  of  the  blood 
The  Cheyne-Stokes  respiration 
The  effects  of  variations  on  tl)e  atmospheric  pressure 
The  influence  of  respiration  on  the  circulation 

General 

Comparative 

The  respiration  and  circulation  in  asphyxia 

Pathological 

Peculiar  respiratory  movements    . 
Coughing,  Uughing,  etc. 

Comparative 

Special  considerations 


blood 


on  respiration 


881 


892 


aBit^9Bf0m»i?!.*ti 


858 


893 


CiJNTENTS. 

Pathological  and  chemical     . 
Personal  observation 
Evolution        .... 
Summary  of  the  physiology  of  respiration 

PRtyrECTITE  AND  ExCRETOkT   FUNCTIOMS  OF  THE  SKIN 

General 

Comparative    .... 
The  excretory  function  of  the  skin 

Normal  sweat  .... 

Pathological    .... 

Comparative — Respiration  by  the  skin 

Death  from  suppression  of  the  functions  of  the  skin 
The  excretion  of  perspiration 

Experimental .... 

Human  physiology . 

Absorption  by  the  skin  . 

Comparative    .       .       . 

Summary        .... 

EsCftETION  BT  THE  KiDNET 

Anatomical     .        .       .        . 
Comparative    .... 
Urine  considered  physically  and  chemically 
Specific  gravity      .... 
Color       .       .       .       .     •  ■ 

Reaction 

Quantity 

Composition :  Nitrogenous  crystalline  bodies 
Non-nitrogenous  organic  bodies . 
Inorganic  salts    .... 
Abnormal  urine      .... 

Comparative 

The  secretion  of  urine   .... 
Methods  of  investigation 
Theories  of  secretion      .       ... 
Nervous  influence  .... 

Pathological 

The  expulsion  of  urine  .... 

Gleneral  ...... 

Facts  of  experiment  and  of  experience 

Pathological 

Comparative 

Summary  of  urine  and  the  functions  of  the  kidneys 
The  Metabolibh  op  the  Body 
General  remarks 
The  metabolism  of  the  liver  . 
The  glycogenic  function 
The  uses  of  glycogen 
Pathological    .... 
Metabolism  of  the  spleen 
Histological    . 


XVll 

PAOB 

406 
,  406 
,  409 
,  410 
,  412 
,  413 
,  418 
,  416 
,  415 
,  415 
,  415 
.  416 
.  416 
.  416 
.  417 
.  418 
.  418 
.  418 
.  410 
.  419 
.  419 
;  423 
.  422 
.  423 
.  428 
.  428 
.  428 
.  424 
.  424 
.  425 
.  426 
.  426 
.  426 
.  427 
.  428 
.  4S» 
.  429 
.  429 


480 
480 
481 
481 
482 
483 
484 
486 
486 
486 


»IMi«M»«iW^'>WW-l«°-W.  Ml.- 


jj^ili  ANIMAL  PHYSIOLOGY. 

Ghemicftl ^^ 

Spleen  carrm ^**    • 

The  nerroos  system  in  lelation  to  the  q>leen 489 

The  oonstraotion  of  fat **® 

General  and  experimental ^ 

Histological *** 

Changes  in  the  cells  of  the  mammary  gland  .       .  .    4tt 

Milk  and  colostrum •    **^ 

Nature  of  fat-formation •       •    *** 

Pathological   .  •  •    ^^ 

Comparative *** 

The  metabolic  processes  concerned  in  the  formation  of  urea,  uric  acid, 

hippuric  acid,  and  allied  bodies 446 

General  discussion 448 

Pathological 448 

Evolution •       •    448 

The  study  of  the  metabolic  processes  by  other  methods      ....    449 

Various  tabuhur  statements 400 

Starvation  and  its  lessons 400 

Comparative    . 408 

Dieto •    *» 

Feeding  experiments 404 

General 464 

Proteid  metabolism  455 

Nitrogenous  equilibrium  •    466 

Comparative 466 

The  effects  of  gelatine  in  the  diet 457 

Fat  and  carbohydrates 467 

Comparative 468 

The  effects  of  salts,  water,  etc.,  on  the  diet    ......    458 

Pathological 409 

The  energy  of  the  animal  body 409 

Tabular  statements 460 

The  sources  of  muscular  energy 461 

Animal  heat 461 

General .461 

Comparative 461 

The  regulation  of  temperature •       •    464 

Cold-blooded  and  warm-blooded  animals  compared  .    465 

Theories  of  heat  formation  and  heat  regulation 466 

Puthological 467 

Special  considerations 467 

Bvolution  . 468 

Hibernation 470 

Daily  variations  in  temperature  in  man  and  other  mammals  .    470 

The  influence  of  the  nervous  system  on  metabolism  (natritton)  .  .    471 

Bxperiioental  facts 471 

Discussion  of  their  signiflcanoe  •       •    4n 

General  considerations,  chemical  and  pathdogioal       ....    476 

-  Bomnuury  of  metabdism 470 


CONTENTS. 


xix 


icid. 


PAOB 

Tm  Spinal  Gobd— Obiiirai< 480 

General 480 

Anatomical 482 

The  reflex  functions  of  the  spinal  cord 484 

General  and  experimental 484 

Erolation  and  heredity 48S 

Inhibition  of  reflexes      . 485 

Reflex  time 486 

The  spinal  cotd  as  a  conductor  of  imjmlaes 487 

Anatomical 488 

Deousaation 480 

Pcthologioal 480 

Paths  of  impulses tfl 

The  automatic  functions  of  the  spinal  cord 488 

General 408 

Spinal  phenomena 408 

Special  considerations 485 

Comparative 405 

Evolution 480 

Synoptical      . 487 

The  Bbaw .486 

GenenJ  and  anatomical 486 

Aninuds  diprived  of  their  cerebrum SOO 

Behavior  of  various  animals  and  its  signiflcance 500 

Have  the  ;iemioirDnlar  canals  a  co-ordinary  function  t        .       .       .       .    502 

Experimental,  etc 502 

Discussion  of  the  phenomena 502 

Fcnoed  movements 608 

Functions  of  the  cerebral  convolutions 504 

Comparative 505 

Individual  dilterences  in  brains 518 

The  connection  of  one  part  of  the  brain  with  another ....    518 

The  cerebral  cortex 521 

Theories  of  dilterent  ofaserven       ........    582 

The  droulation  in  the  brain «...    825 

8lam>— hibernation— dreaming 526 

Hypnotism— catalepsy— somnambulism 628 

Firthologioal 580 

Cenbal  looalixation  reconsidered 580 

Illustrations  of  looalixation    .  ...       . "    .  .       .   685 

Different  methods  criticised ,       .    886 

Cerebral  time 686 

Fonotiont  of  other  portions  of  the  brain 886 

The  corpus  striatum  and  the  optic  thalamus 686 

Corpora  quadrigemina 680 

The  cerebellum 641 

PMhological 641 

Crura  cerebri  and  and  pons  Varolii 641 

Pathological .      '.       .       .       .    642 

Medulla  oblongata 642 


XX 


ANIMAL  PHYSIOLOGY. 


Special  considetBtions   . 
Embryological 
Evolution 
Synoptical 
Gknekal  Remarks  cm  tbb  Sinses 
Anatomical 
General  principles  . 
The  Skin  as  ak  Organ  ok  Sense 
Gtoneral    . 
Pathological    . 
Pressure  senrntions 
Thermal  sensations 

Tactile  sensibility  . 
The  muscular  sense 
General   . 
Pathological   . 
Comparative  . 
Synoptical 
Vision       .... 
Physical  . 
Anatomical     . 
Embryological 
Dioptrics  of  vision 
Accommodation  of  the  eye 
Alterations'  in  the  si»  of  the  pupil 
°  Phenomena  and  their  explanations 
Pathological   . 
Optical  imperfections  of  the  eye 
Spherical  aberration 
Astigmatism  . 
Chromatic  aberration 
Entoptic  phenomena 
Anomalies  of  refraction 
Visual  sensations  . 
General   . 

Affections  of  the  retina 

The  nature  of  the  processes  which  originate  visual 
The  laws  of  retinal  stimulation 
The  visual  angle 
Color  sensations 
Theories  of  color-vision  . 
Color-blindness 
Ptychologioal  aspects  of  vision 
The  visual  field 
Imperfections  of  visual  perceptions  as  •*  Irradiation," 
Influence  of  the  pigment  of  the  macula  lutea 

After-images,  etc. 

Misconceptions  as  to  the  oompanitive  size  of  objects 
Subjective  phenomena    . 
Co-ordination  of  the  two  eyes  In  vision 


impulses 


etc. 


^.^iwM>f(^'Mi<>^;;4i^4t44  ^  fcat^ 


mm- 


vision 


CONTENTS. 


The  visual  axes 

Ocular  movements  . 

The  horopter  .... 

Estimation  of  the  size  and  distance  of  objects 

Solidity 

Protective  mechanisms  of  the  eye 
Special  considerotious   .       .       . 
Copiparative    . 
Evolution        .        .       . 
Pathological    .... 
Brief  synopsis  of  the  physiology  of 

Ukarino 

General 

Anatomical     .... 
The  membrana  tympani 
The  auditory  ossicles     . 
Muscles  of  the  middle  ear 
The  Eustachian  tube 
Pathological    .... 
Auditory  impulses  . 
Auditory  sensations,  perceptions,  judgments 

Oeneral 

Auditory  judgment 
Range  of  auditory  discrimination 
Special  considerations    . 

Comparative   .... 
Evolution        .... 
Synopsis  of  the  physiology  of  hearing 
The  Sense  of  Shell 

Anatomical     .       .       .       < 
General    .       .       .       •       < 
Comparative   ... 
The  Seitse  of  Taste 

Anatomical     .       .       • 
General    .... 
Experimental  . 
Pathological    . 
Comparative    . 
The  Cerbbbo-Spinal  System  of  Nerves 

1.  Spinal  nerves    .... 

General 

Exception       .... 
Additional  experiments . 
Pathological  .... 

2.  The  cranial  nerves    . 

General 

The  motor-oculi,  or  third  nerve 
The  trochlear,  or  fourth  nerve 
The  abducens,  or  sixth  neree . 
The  facial,  or  seventh  nerve  . 


xxi 

501 

C04 

5r> 

605 
596 
598 
597 
600 
602 
603 
604 
604 
605 
600 
607 
,  606 
,  600 
,  609 
.  610 
.  615 
.  615 
.  615 
.  616 
.  616 
.  616 
.  618 
.  620 
.  620 


626 


627 
627 
627 


]  ■-, 


i.,.-t 


BWteajwwMww^ 


xxu 


ANIMAL  PHYSIOLOGY. 


The  trigeminus,  or  fifth  nerve 

The  glosso-pharyngeal,  or  ninth  nerve 

The  pneumogastric,  or  tenth  nerve 

The  spinal  accessory,  or  eleventh  nerve 

The  hypoglossal,  or  twelfth  nerve . 
Relations  of  the  cerebro-spinal  and  sympathetic  systems 

Recent  views  on  this  subject , 
The  Voice  and  Speech  . 

Physical .... 

Anatomical     ... 

Laryngoscopic  observations  . 

Voice-formation 

The  registers  and  the  falsetto-voice 

Pathological 

Comparative 
Speech   . 

General    . 

Formation  of  vowels  and  consonants 

Whispering     . 

Classification  of  consonants 

Pathological    . 
Special  considerations    . 

Evolution 

Summary 
Locomotion       .... 

Anatomical     .     •'■. 

Mechanical 

Standing. 

Walking. 

Running. 

Jumping .... 

Hopping .... 

Comparative :  the  gait  of  quadrupeds 

Evolution 
Man  considbrbd  physiolooicau.y 
Existence 

Sixe  and  growth 

Digestive  system 

Circulatory  and  respiratory  systems 

Dentition 

Nervous  system 

Puberty  . 

The  sexes 

Old  age   . 

Comparative 

Death 
Appendix:  Animal  Cbxmutrt 
Index        .       .       .       ,  .     ^ 


AT 


THE 


DirrxBENT  Pbkiodb  or  bib 


680 


640 
648 
648 
644 
646 
647 
640 
640 
660 
660 
661 
661 
662 


666 
666 
666 
666 

667 
660 
660 
060 
650 


664 
664 
666 
666 
666 
667 
667 
666 
668 
671 
601 


■*SflWtTfr!fl1<SW"-.  ■.  i'> 


•^  smf'!^^^l»i''ISti^JV»^ 


'^mum 


680 


688 


iMyiiiMiiiiMMiMmyMimiiw&iMiMii 


AKEMAL  PHYSIOLOGY. 


659 


650 


GENERAL  BIOLOGY. 
Introduction. 

BiOLOOY  ifitoi,  life;  Aoyot,  a  dissertation)  is  the  science 
which  treats  of  the  nature  of  living  things;  and,  since  the 
properties  of  plants  and  animals  can  not  be  explained  without 
some  knowledge  of  their  form,  this  science  includes  morphol- 
ogy (fuv^f  form ;  Xoyot,  a  dissertation)  as  well  as  physiology 
(^wrw,  nature ;  Aoyw). 

'  Morphology  describes  the  various  forms  of  living  things 
and  their  parts ;  physiology,  their  action  or  function. 

(General  biology  treats  neither  of  animals  nor  plants  exclu- 
sively. Its  province  is  neither  aodlogy  nor  botany ;  but  it  at- 
tempts to  define  what  is  common  to  all  living  things.  Its  aim 
is  to  determine  the  properties  of  organic  beings  as  such,  rather 
than  to  classify  or  to  give  an  exhaustive  account  of  either  ani- 
mals or  planto.  Manifestly,  before  this  can  be  done,  living 
things,  both  animal  and  vegetable,  must  be  carefully  compared, 
otherwise  it  would  be  impossible  to  recognize  differences  and 
resemblances ;  in  other  words,  to  ascertain  what  they  have  in 
common. 

When  only  the  highest  animals  and  plants  are  contem- 
plated, the  differences  between  them  seem  so  vast  that  they 
i^pear  to  have,  at  first  sight,  nothing  in  common  but  that  they 
are  living:  between  a  tree  and  a  dog  an  infant  can  discrimi- 
nate; but  there  are  microscopic  forms  of  life  that  thus  far 
defy  the  most  learned  to  say  whether  they  belong  to  the  ani- 
mal or  the  vegetable  world.  As  we  descend  in  the  organic 
series,  the  lines  of  distinction  grow  fainter,  till  they  seem 
finally  to  all  but  disappear. 

But  let  us  first  inquire :  What  are  the  determining  charao- 
1 


ii/i'iv'ji''  *■■  :-'''"-'~<~^' 


imWrttohHTTi  *■»  ^f  frm  n^  n'  rawi  w?^  iBiTy  iWWilWWii  iiW 


tttmrnnmsss. 


ANIMAL  PHYSIOLOOT. 


teristics  of  living  things  as  such  ?  By  what  barriers  are  the 
animate  and  inanimate  worlds  separated?  To  decide  this, 
falls  within  the  province  of  general  biology. 

Living  things  grow  by  interstitial  additions  of  particles  of 
matter  derived  from  without  and  transformed  into  their  own 
substance,  while  inanimate  bodies  increase  in  size  by  superfi- 
cial additions  of  matter  over  which  they  have  no  power  of 
decomposition  and  recomposition  so  as  to  make  them  like 
themselves.  Amonj^  lifeless  objects,  crystals  approach  near- 
est to  living  forms ;  but  the  crystal  builds  itself  up  only  from 
material  in  solution  of  the  same  chemical. composition  as  itself. 

The  chemical  constitution  of  living  objects  is  peculiar.  Car- 
bon, hydrogen,  oxygen,  and  nitrogen  are  combined  into  a  very 
complex  whole  or  molecule,  as  protein;  and,  when  in  com- 
bination with  a  large  proportion  of  water,  constitute  the  basis 
of  all  life,  animal  and  vegetable,  known  as  protoplasm.  Only 
living  things  can  manufacture  this  substance,  or  even  protein. 

Again,  in  the  very  nature  of  the  case,  protoplasm  is  con- 
tinually wasting  by  a  process  of  oxidation,  and  being  built  up 
from  simpler  chemical  forms.  Carbon  dioxide  is  an  invariable 
product  of  this  waste  and  oxidation,  while  the  rest  of  the  car- 
bon, the  hydrogen,  oxygen,  and  nitrogen  are  given  back  to  the 
inorganic  kingdom  in  simpler  forms  of  combination  than  those 
in  which  they  exist  in  living  beings.  It  will  thus  be  evident 
that,  while  the  flame  of  life  continues  to  bum,  there  is  constant 
chemical  and  physical  change.  Matter  is  being  continuously 
taken  from  the  world  of  things  that  are  without  life,  trans- 
formed into  living  things,  and  then  after  a  brief  existence  in 
that  form  returned  to  the  source  from  which  they  were  origi- 
nally derived.  It  is  true,  all  animals  require  their  food  in  or- 
ganized form— that  is,  they  either  feed  on  animal  or  plant 
forms ;  but  the  latter  derive  their  nourishment  from  the  soil 
and  the  atmosphere,  so  that  the  above  statement  is  a  scientific 
truth. 

Another  highly  characteristic  property  of  all  living  things 
is  to  be  sought  in  their  periodic  changes  and  very  limits  dura- 
tion. Every  animal  and  plant,  no  matter  what  its  rank  in  the 
scale  of  existence,  begins  in  a  simple  form,  passes  through  a 
series  of  changes  of  varying  degrees  of  complexity,  and  finally 
declines  and  dies ;  which  simply  means  that  it  rejoins  the  in- 
animate kingdom:  it  passes  into  another  world  to  which  it 
formerly  belonged. 

Living  things  alone  give  rise  to  living  things;  protoplasm 


are  the 
de  this, 

iiicles  of 
leir  own 

superfi- 
)ower  of 
lem  like 
ch  near- 
ttly  from 
as  itself, 
ar.  Car- 
K>a  very 
in  com- 
the  basis 
a.  Only 
protein. 
1  is  con- 
built  np 
ivariable 

the  car- 
ck  to  the 
lan  those 
a  evident 
constant 
binuously 
f e,  trans- 
istence  in 
ere  origi- 
>od  in  or- 
or  plant 
1  the  soil 
scientific 

ng  things 
it6ddur»> 
ok  in  the 
hrough  a 
nd  finally 
IS  the  in- 
whioh  it 

rotoplasm 


GENERAL  BIOLOOT.  $ 

alone  can  beget  protoplasm;  cell  begets  cell.  Omne  animal 
{anima,  life)  ex  ovo  applies  with  a  wide  interpretation  to  all 
living  forms. 

From  what  has  been  said  it  will  appear  that  life  is  a  condi- 
tion of  ceaseless  change.  Many  of  the  movements  of  the  pro- 
toplasm composing  the  cell-units  of  which  living  beings  are 
made  are  visible  under  the  microscope ;  their  united  effects  are 
open  to  common  observation — as,  for  example,  in  the  move- 
ments of  animals  giving  rise  to  locomotion  we  have  the  joint 
result  of  the  movements  of  the  protoplasm  composing  millions 
of  muscle-cells.  But,  beyond  the  powers  of  any  microscope  that 
has  been  or  probably  ever  will  be  invented,  there  are  molecular 
movements,  ceaseless  as  the  flow  of  time  itself.  All  the  processes 
which  make  up  the  life-history  of  organisms  involve  this  mo- 
lecular motion.  The  ebb  and  flow  of  the  tide  may  symbolize 
the  influx  and  efflux  of  the  things  that  belong  to  the  inanimate 
world,  into  and  out  of  the  things  that  live. 

It  follows  from  this  essential  instability  in  living  forms  that 
life  must  involve  a  constant  struggle  against  forces  that  tend 
to  destroy  it ;  at  best  this  contest  is  maintained  successfully  for 
but  a  few  years  in  all  the  highest  grades  of  being.  So  long  as 
a  certain  equilibrium  can  be  maintained,  so  long  may  life  con- 
tinue and  no  longer. 

The  truths  stated  above  will  be  illustrated  in  the  simpler 
forms  of  plants  and  animals  in  the  ensuing  pages,  and  will  be- 
come clearer  as  each  chapter  of  this  work  is  perused.  They 
form  the  fundamental  laws  of  general  biology,  and  may  be 
formulated  as  follows : 

1.  Living  matter  or  protoplasm  is  characterized  by  its  chem- 
ical composition;  being  made  up  of  carbon,  hydrogen,  oatygen, 
and  niirogen,  arranged  into  a  very  complex  molecule. 

2.  Its  universal  and  constant  waste  and  its  repair  by  inter- 
stitial formation  of  new  matter  similar  to  the  old. 

8.  Its  power  to  give  rise  to  new  forms  similar  to  the  parent 
ones  by  a  process  of  division. 

4.  Its  manifestation  of  periodic  changes  constituting  devel- 
opment, decay,  and  death. 

Though  there  is  little  in  relation  to  living  beings  which 
may  not  be  appropriately  set  down  under  zodlogy  or  botany,  it 
tends  to  breadth  to  have  a  science  of  general  biology  which 
deals  with  the  properties  of  things  simply  as  living,  irrespective 
very  much  as  to  whether  they  belong  to  the  realm  of  animals 
or  plants.    The  relation  of  the  sciences  which  may  be  regarded 


aasfttw»*iywii'iW'wi(iiiw«o(iii"<iwMWia' 


tarn 


4  ANIMAL  PHYSIOLOGY, 

as  subdivisions  of  general  biology  is  well  shown  in  the  follow- 
ing table :  * 

Anatomy. 
The  wienoe  of  gtruoture ;  the 
term  being  usuallj  ap- 
plied to  the  coaner  and 
more  obTlous  composition 
of  plants  or  animals. 

BiaMogjf. 
MicKMOopical        anatomy. 
The  ultimate  optical  an- 
alysis of  structure  by  the 
aid  of    the    microscope; 
MUX-  separated  from  anatomy 

phol-  onl;^  as  a  matter  of  con- 

venience. 


BioL- 


science 
of  liv- 
ing   V 
things ; 

i.  e.,  of 

matter 

in  the 

living 

state. 


e 
science 

of 
form, 
struct- 
ure, 
etc. 
Essen- 
tially 
statical. 


Phyii- 

science 

Of 
action 

or 
func- 
tion. 

Essen- 
tially 

dynam- 
ical. 


Taceontmy. 
The  classification  of  living 
things,  based  chiefly  on 
phenomena  of  structure. 

IHttribution. 
Considers  the  ftosition  of  liv- 
ing things  in  space  and 
time ;  their  distribution 
over  the  present  face  of 
the  earth ;  and  their  distri- 
bution and  succession  at 
former  periods,  as  dis- 
pUyed  in  fossil  remains. 

EtiAryoloffy. 

The  science  of  development 
from  the  jgerm ;  includes 
many  mned  problems 
pertaining  both  to  mor- 
phology and  physiology. 
At  present  largely  mor- 
phologioaL 

Phyaiology. 

The  special  science  of  the 
functions  of  the  individ- 
ual in  health  and  in  dis- 
ease; hence  including 
Patlulogy. 

Ptyehdtogy. 

The  science  of  mental  phe- 
nomena. 

SoeMogy. 
The  science  of  social  life, 
i.  e.,  the  life  of  communi- 
ties, whether  of  men  or 
of  lower  animals. 


Botany. 

The 
science 
of  veg- 
etal 
living 
matter 

or 
plants. 


Zofll- 


le 
science 

of 
animal 
living 
matter 
or  ani- 
mals. 


ma.' 

The 
science 
of  liv- 
ing 
things ; 
i.  e.,  of 
matter 
in  the 
living 
state. 


•  Taken  from  the  "General  Biology"  of  Sedgwick  and  Wilson. 


awtBW^MwawMMWMiWBw*^^ 


THE  CELL. 


THE   CELXi.* 


All  living  things,  great  and  small,  are  composed  of  cells. 
Animals  may  be  divided  into  those  consisting  of  a  single  cell 
(Protozoa),  and  those  made  up  of  a  multitude  of  cells  {Meiazoa) ; 
but  in  every  case  the  animal  begins  as  a  single  cell  or  ovum 
from  which  all  the  other  cells,  however  different  finally  from 
one  another  either  in  form  or  function,  are  derived  by  processes 
of  growth  and  division ;  and,  as  will  be  seen  later,  the  whole 
organism  is  at  one  period  made  up  of  cells  practically  alike  in 
structure  and  behavior.  The  history  of  each  individual  animal 
or  plant  is  the  resultant  of  the  conjoint  histories  of  each  of  its 
cells,  as  that  of  a  nation  is,  when  complete,  the  story  of  the 
total  outcome  of  the  lives  of  the  individuals  composing  it. 

It  becomes,  therefore,  highly  important  that  a  clear  notion 
of  the  characters  of  the  cell  be  obtained  at  the  outset;  and 
this  chapter  will  be  devoted  to  presenting  a  general  account  of 
the  cell. 

The  cell,  whether  animal  or  vegetable,  in  its  most  complete 
form  consists  of  a  mass  of  viscid,  semifluid,  transparent  sub> 
stance  {protoplasm),  a  cell  wall,  and  a  more  or  less  circular  body 
(nudeua)  situated  generally  centrally  within ;  in  which,  again, 
is  found  a  similar  structure  {nucleoliia). 

This  description  applies  to  both  the  vegetable  and  the  ani- 
mal cell ;  but  the  student  will  find  that  the  greater  proportion 
of  animal  cells  have  no  cell  wall,  and  that  very  few  vegetable 
cells  are  without  it.  But  there  is  this  great  difference  between 
the  animal  and  vegetable  cell :  the  former  never  has  a  ceUuloae 
wall,  while  the  latter  rarely  lacks  such  a  covering.  In  every 
case  the  cell  wall,  whether  in  animal  or  vegetable  cells,  is  of 
greater  consistence  than  the  rest  of  the  cell.  This  is  especially 
true  of  the  vegetable  ceU. 

It  is  doubtful  whether  there  are  any  cells  without  a  nucleus, 
while  not  a  few,  especially  when  young  and  most  active,  pos- 
sess several.  The  circular  form  may  be  regarded  as  the  typical 
form  of  both  cells  and  nuclei,  and  their  infinite  variety  in  size 
and  form  may  be  considered  as  in  great  part  the  result  of  the 
action  of  mechanical  forces,  such  as  mutual  pressure ;  this  is, 
of  course,  more  especially  true  of  shape.  Reduced  to  its  great- 
est, simplicity,  then,  the  cell  may  be  simply  a  mass  of  protoplasm 
with  a  nucleus. 

*  The  Uliutnitions  of  the  sections  following  will  enable  tlie  student  to  form  • 
genemliied  mental  piotura  of  the  cell  in  all  its  parts. 


6 


ANIMAL  PHTSIOLOOT. 


It  seems  probable  that  the  numerous  researches  of  recent 
years  and  others  now  in  progress  will  open  up  a  new  world  of 
cell  biology  which  will  greatly  advance  our  knowledge,  espe- 
cially in  the  direction  of  increased  depth  and  accuracy. 

Though  many  points  arer  still  in  dispute,  it  may  be  safely 
said  that  the  nucleus  plays,  in  most  cells,  a  rdfe  of  the  highest 
importance ;  in  fact,  it  seems  as  though  we  might  regard  the 
nucleus  as  the  directive  brain,  so  to  speak,  of  the  individual 
cell.  It  frequently  happens  that  the  behavior  of  the  body  of 
the  cell  is  foreshadowed  by  that  of  the  nucleus.    Thma  fre- 


dlnairaute.   B.  preparinc  for  dlvMon ;  tiw  contour  ia  lew  defined,  siid  tte  ttbmtliMter 

nuiid  the  equntoro^  the  MhronwUn  spindle,  p,  monMt«Mti«e  5  the  ^on»to  nbw 
^VM"  ••  wntripetia  equntorial  Ve.  eS^of  which  *g»4*be»pwsept5d  »  double. 
KiTmigration  of  the  hJifol  eMh  chromatin  loop  towwda  oppoaite  doIm  ot  tin  19^^ 
tI  dla«5r4«age ;  the  chromatin  forma  a  atar^  round  .each  pole  pi  a  attodle.  aadi  a^be; 
faw  connectoS  by  etranda  of  achromatln.  O, daughter-wnadi {to|B j  titet^br formed 
•ii»i«<  mre,  MMlns  throuofa  their  retrosreaalTe  devekMiment,  whlcb.to  completed,  in  the 


polar  star  at  the  end  of  the  fqiindle  to  compoaed  M  protopiaam-ctranuiea  «  ""  ""iJSS' 
S^uat  not  be  mtotaken  fortito  ^artwr  (Fl.  THe  <»f«  ««»  "KJSH*  «5^JEf^ 
the  line  Unea  the  achromadn,  and  the  dotted  Unea  oeU««natoa.  (OhMhr  modllled  from 
nemmW.)  X-Z.  diraotradear  dlviaton  In  the  odto  of  the  embryonic  integument  of  the 
Buiopean  aoorpion.    After  Bloohmann  (Haddon). 

quently,  if  not  always,  division  of  the  body  of  the  nucleus  pre- 
cedes that  of  the  cell  itself,  and  is  of  a  most  complicated  cliar- 
acter  {karyokineaia  or  mitoais).  The  cell  wall  is  of  subordinate 
importance  in  the  processes  of  life,  though  of  great  value  as  a 
mechanical  support  to  the  protoplasm  of  the  cell  andthe  aggre- 


THE  CELL. 


gations  of  cells  known  as  tissues.  The  greater  part  of  a  tree 
may  be  said  to  be  made  up  of  the  thickened  walls  of  the  cells, 
and  these  are  destitute  of  true  vitality,  unless  of  the  lowest 
order ;  while  the  really  active,  growing  part  of  an  old  and  large 
tree  constitutes  but  a  small  and  limited  zone,  as  may  be  learned 
from  the  plates  of  a  work  on  modem  botany  representing  sec- 
tions of  the  wood. 

Animals,  too,  have  their  rigid  parts,  in  the  adult  state  espe- 
cially, resulting  from  the  thickening  of  a  part  or  the  whole  of 
the  cell  by  a  deposition  usually  of  salts  of  lime,  as  in  the  case  of 
the  bones  of  animals.  But  in  some  cases,  as  in  cartilage,  the 
cell  wall  or  capsule  undergoes  thickening  and  consolidation, 
and  several  may  fuse  together,  constituting  a  matrix,  which  is 
also  made  up  in  part,  possibly,  of  a  secretion  from  the  cell  pro- 
toplasm. In  the  outer  parts  of  the  body  of  animals  we  have  a 
great  abundance  of  examples  of  thickening  and  hardening  of 
cells.  Very  well  known  instances  are  the  indurated  patches  of 
ffkin  {epUTielivm)  on  the  palms  of  the  hands  and  elsewhere. 

It  will  be  scarcely  necessary  to  remark  that  in  cells  thus 
altered  the  mechanical  has  largely  taken  the  place  of  the  vital 
in  function.  This  at  once  harmonizes  with  and  explains  what 
is  a  matter  of  common  observation,  that  old  men  are  less  active 
—have  less  of  life  within  them,  in  a  word,  than  the  young. 
Chemically,  the  cellulose  wall  of  plant-cells  consists  of  carbon, 
hydrogen,  and  oxygen,  in  the  same  relative  proportion  as  exists 
in  starch,  though  its  properties  are  very  difEerent  from  those  of 
that  substance. 

Turning  to  cell  contents,  we  find  them  everywhere  made  up 
of  a  clear,  viscid  substance,  containing  almost  always  granules 
of  varying  but  very  minute  size,  and  differing  in  consistence, 
not  only  in  different  groups  of  cells,  but  often  in  the  same  cell, 
so  that  we  can  distinguish  an  outer  portion  {edopkum)  and  an 
inner  more  fluid  and  more  granular  reg^ion  {endoplaam). 

The  nucleus  is  a  body  with  very  clearly  defined  outline  (in 
some  cases  limited  by  a  membrane),  throughwhich  an  irregu- 
lar network  of  fibers  extends  that  stains  more  deeply  than  any 
other  part  of  the  whole  cell. 

Owing  to  the  fact  that  it  is  so  readily  changed  by  the  action 
of  reagents,  it  is  impossible  to  ascertain  the  exact  chemical  com- 
position of  living  protoplasm;  in  consequence,  we  can  only 
infer  its  chemical  structure,  etc.,  from  the  examination  of  the 
dead  substance. 

In  general,  it  may  be  said  that  protoplasm  belongs  to  the 


' ; 


i 


8 


ANIMAL  PHTSI0L06T. 


class  of  bodies  known  as  proteids — that  is,  it  consists  chemically 
of  carbon,  hydrogen,  a  little  sulphur,  oxygen,  and  nitrogen,  ar- 
ranged into  a  very  complex  and  unstable  molecule.  This  very 
instability  seems  to  explain  at  once  its  adaptability  for  the 
manifestation  of  its  nature  as  living  matter,  and  at  the  same 
time  the  readiness  with  which  it  is  modified  by  many  circum- 
stances ,  so  that  it  is  possible  to  understand  that  life  demands 
an  incessant  adaptation  of  internal  to  external  conditions. 

It  seems  highly  probable  that  protoplasm  is  not  a  single  pro- 
teid  substance,  but  a  mixture  of  such ;  or  let  us  rather  say,  fur- 
nishes these  when  chemically  examined  and  therefore  dead. 

Very  frequently,  indeed  generally,  protoplasm  contains  other 
substances,  as  salts,  fat,  starch,  chlorophyl,  etc. 

From  the  fact  that  the  nucleus  stains  differently  from  the 
cell  contents,  we  may  infer  a  difference  between  them,  physical 
and  especially  chemical.  It  (nucleus)  furnishes  on  analysis  nu- 
cZem,  which  contains  the  same  elements  as  protoplasm  (with  the 
exception  of  sulphur)  together  with  phosphorus.  Nuclei  have 
great  resisting  power  to  ordinary  solvents  and  even  the  digest- 
ive juices. 

Inasmuch  as  all  vital  phenomena  are  associated  with  proto- 
plasm, it  has  been  termed  the  "  physical  basis  of  life  "  (Hux- 
ley). 

TiMiiM. — A  collection  of  cells  performing  a  similar  physio- 
logical action  constitutes  a  tissue. 

(Generally  the  cells  are  held  together  either  by  others  with 
that  sole  function,  or  by  cement  material  secreted  by  them- 
selves. An  orgcm  may  consist  of  one  or  several  tissues.  Thus 
the  stomach  consists  of  muscular,  serous,  connective,  and  gland- 
ular tissues  besides  those  constituting  its  blood-vessels,  lym- 
phatics, and  nerves.  But  all  of  the  cells  of  each  tissue  have, 
speaking  generally,  the  same  function.  The  student  is  referred 
to  works  on  general  anatomy  and  histology  for  classifications 
and  descriptions  of  the  tissues. 

The  statements  of  this  chapter  will  find  illustration  in  the 
pages  immediately  following,  after  which  we  shall  return  to 
the  subject  of  the  cell  afresh. 

lauuurj. — ^The  typical  cell  consists  of  a  wall,  protoplasmic 
contents,  and  a  nucleus.  The  vegetable  cell  1^  a  limiting 
membrane  of  cellulose.  Oells  undergo  differentiation  and  may 
be  united  into  groups  forming  tissues  which  serve  one  or  more 
definite  purposes. 

The  chemical  constitution  of  protoplasm  is  highly  complex 


nNICBLLULAB  PLANTa 


9 


and  unstable.  The  nucleus  plays  a  prominent  part  in  the  life- 
history  of  the  cell,  and  seems  to  be  essential  to  its  perfect  devel- 
opment and  greatest  physiological  efficiency. 


F».r 


UNICELLULAR  PLANTS. 
Ybast  {Torukt,  Saccharomycea  Cerevisue). 

The  essential  part  of  the  common  substance,  yeast,  may  be 
studied  to  advantage,  as  it  affords  a  simple  type  of  a  vast  group 
of  organisms  of  profound 
interest  to  the  student  of 
physiology  and  medicine. 
To  state,  first,  the  main 
facts  as  ascertained  by 
observation  and  experi- 
ment : 

XorphologiaaL  —  The 
particles  of  which  yeast 
is  composed  are  cells  of  a 
circular  or  oval  form,  of 
an  average  diameter  of 
about  x^  of  an  inch. 

Each  individual  tortda 
cell  consists  of  a  trans- 
parent homogeneous  cov- 
ering {ceHuloae)  and  gran- 
ular semifluid  contents 
{protoplaam).  Within  the 
latter  there  may  be  a 
space  (vacuole)  filled  with 
more  fluid  contents. 

The  various  cells  pro- 
duced  by   buddinjr   may   t*.  L-rhe  endogonldte  (Meoapore)  phiM  of 
.,     ....        ,    ,      '  dnetton— I. e., endoniMHia diTiaion. 

remain  united  like  strings 
of  beads.  Collections  of 
masses  composed  of  four 
or  more  subdivisions  {aa- 
eoaporea),  which  finally 
separate  by  rupture  of 
the  original  cell  wall,  having  thus  become  themselves  inde- 
pendent cells,  may  be  seen  more  rarely  (endogenous  division). 


VarfoH  ■tagM  In  tiM  derekminent  of  brewer<a 
yeaat,  aeen,  with  the  ezaeption  of  the  first  in  the 
Mriea,  with  Ml  ordtaHuy  h](^  power  (Zeia*.  D.  4)  of 
the  micraaoope.  The  flrat  b  greatly  masniaed 
(Gundlacfa^^linineiaionlena).  Theaecondaeriea 
of  (oar  rapreaenta  atagea  in  the  diTialon  of  a  ainffie 
oril ;  amf  the  third  aerlea  a  branclifaur  oolonr. 
BTMTwlMfe  the  li(^  areaa  indicate  Tacuolea, 


FBpVO- 


WW 


Fw.4.— Itethar  dwetopment  of  the  forma  rcpreaented 
In  Fig.  8. 


10 


ANIMAL  PHT8I0L00T. 


I     ! 


The  yeast-cell  is  now  believed  to  possess  a  nudeua. 

Ohamisal. — When  yeast  is  burned  and  the  ashes  analyzed, 
they  are  found  to  consist  chiefly  of  salts  of  potassium,  calcium, 
and  magnesium. 

The  elements  of  which  yeast  is  composed  are  C,  H,  O,  N,  S, 
P,  K,  Mg,  and  Ca ;  but  chiefly  the  first  four. 

nfriologieaL — If  a  little  of  the  powder  obtained  by  drying 
yeast  at  a  temperature  below  blood-heat  be  added  to  a  solution 
of  sugar,  and  the  latter  be  kept  warm,  bubbles  of  carbon  di- 
oxide will  be  evolved,  causing  the  mixture  to  become  frothy ; 
and  the  fluid  will  acquire  an  alcoholic  character  {fermerUa- 
iion). 

If  the  mixture  b^  raised  to  the  boiling-point,  the  process  de- 
scribed at  once  ceases. 

It  may  be  further  noticed  that  in  the  fermenting  saccharine 
solution  there  is  a  gradual  increase  of  turbidity.  AH  of  these 
changes  go  on  perfectly  well  in  the  total  absence  of  sunlight. 

Teast-cells  are  found  to  grow  and  reproduce  abundantly  in 
an  artificial  iv>d  solution  consisting  of  a  dilute  solution  of  cer- 
tain salts,  togf:.ther  with  sugar. 

GonduibMi— What  are  the  conclusions  which  may  be  legiti- 
mately drawn  from  the  above  facts  P 

That  the  essential  part  of  yeast  consists  of  cells  of  about  the 
size  of  mammalian  blood-corpuscles,  but  with  a  limiting  wall 
of  a  substance  different  from  the  inclosed  contents,  which  latter 
is  composed  chiefly  of  that  substance  common  to  all  living 
things— protoplasm ;  that  like  other  cells  they  reproduce  their 
J.  ind,  and  in  this  instance  by  two  methods :  gemmation  giving 
rise  to  the  bead-like  aggregations  alluded  to  above;  and  in- 
ternal division  of  the  protoplasm  {endogetunu  diviaion). 

From  the  circumstances  under  which  growth  and  reproduc- 
tion take  place,  it  will  be  seen  that  the  original  protoplasm  of 
the  cells  may  increase  its  bulk  or  grow  when  supplied  with 
suitable  food,  which  is  not,  as  will  be  learned  later,  the  same  in 
all  respects  as  that  on  which  green  plants  thrive ;  and  that  this 
may  occur  in  darkness.  But  it  is  to  be  especially  noted  that  the 
protoplasm  resulting  from  the  action  of  the  living  cells  is 
wholly  different  from  any  of  the  substances  used  as  food.  This 
power  to  construct  protoplasm  from  inanimate  and.  unorgan- 
ized materials,  reproduction,  and  fermentation  are  all  proper- 
ties characteristic  of  living  organisms  alone. 

It  will  be  further  observed  that  these  changes  all  take  place 
within  narrow  limits  of  temperature;  or,  to  put  the  matter 


-vimmam 


CNICEM     LAR  PLANTS. 


11 


3  analyzed, 
tn,  calcium, 

H,  O,  N,  S, 

I  by  drying 
o  a  solution 

carbon  di- 
>me  frothy; 

{fermentor 

)  process  de- 

j  saccharine 
All  of  these 
;  sunlight, 
tundantly  in 
ation  of  cer- 

ay  be  legiti- 

of  about  the 
imiting  wall 
which  latter 
»  all  living 
trodnce  their 
ation  giving 
3ve;  and  in- 
sion). 

nd  reproduc- 
rotoplasm  of 
applied  with 
',  the  same  in 
and  that  this 
oted  that  the 
ving  cells  is 
\atood.  This 
Old  unorgan- 
re  all  proper- 
all  take  place 
t  the  matter 


more  generally     bat  the  li    -history  of  thishu-Hble  >rpaiism 
can  only  be  unfolded  und«?i    ♦^rtH  n       '-defined    ondiuoim. 

PbotococcuS  (Protoco    tis  pluvi(    ,$). 

The  study  of  this  one-celled  f    nt  will  wford  instructive 
comparison  between  the  ordinary  green  iilant  jyid  the  colorless 

plants  or  fungi.  .   ' 

Like  Ibrufa  it  is  selected  because  of  its  simple  nature,  its 
abundance,  and  the  ease  with  which  it  may  be  obtained,  for  it 
abounds  in  water-barrels,  standing  pools,  drinking-troughs,  etc. 
KoipliologiHiL— Protococcus  consists  of  a  structureless  wall 
and  viscid  granular  contents,  i  e.,  of  cellulose  and  protoplasm. 
The  protoplasm  may  contain  starch  and  a  red  or  green  color- 
ing matter  (cWoropfcyl).  It  probably  contains  a  nucleus.  The 
cell  is  mostly  globular  in  form. 


»Hk& 


nc  e.*r. 


thelMrkoCatne. 


obMrred  in  the  HMtMonr  <rf  Fratoooed  MBMMd  fMm 
i^OedrM  Rtato.ilhMMttiwnMtliodo(dlTWDa. 


Fw.  S.-A  groopin 

Sto!  7.I^SigiM  plMMliri^  'WwfmqtOe  Mwe 


1  t.-OM  oCHM  •bom  Aftar  two  di««' 


fai  watflc. 

tqrtbeaboveapeeinMM.   nieini- 


pijglologiML— It  reproduces  by  division  of  the  original  cell 
(fiaaion)  into  simihur  individuals,  and  hf  a  process  of  budding 
and  constriction  {gemmalwn)  which  is  much  rarer.  Under  the 
influence  of  sunlight  it  decomposes  carbon  dioxide  (CO.),  fix- 
ing  the  carbon  and  setting  the  oxygen  free.  It  can  flourish  per- 
f  ectly  in  rain-water,  which  contains  only  carbon  dioxide,  salts 
of  ammonium,  and  minute  quantities  of  other  soluble  salts  that 
may  as  dust  have  been  blown  into  it. 

There  is  a  motile  form  of  this  unicellular  plant,  and  in  this 
stage  it  moves  through  the  fluid  in  which  it  Uves  by  means  of 


19 


ANIMAL  PHYSIOLOGY. 


' 


m 


extensions  of  its  protoplasm  {cUia)  through  the  cell  wall;  or 
the  cell  wall  may  disappear  entirely.  Finally,  the  motile  form, 
withdrawing  its  cilia  and  clothing  itself  with  a  cellulose  coat, 
becomes  globular  and  passes  into  a  quiescent  state  again. 
Much  of  this  part  of  its  history  is  common  to  lowly  animal 
forms. 

OendwUnia. — It  will  be  seen  that  there  is  much  in  common 
in  the  life-history  of  Tonda  and  Proiococcus.  By  virtue  of  be- 
ing living  protoplasm  they  transform  unorganized  material  into 
their  own  substance;  and  they  grow  and  reproduce  by  analo- 
gous methods. 

But  there  are  sharply  defined  differences.  For  the  green 
plant  sunlight  is  essential,  in  the  presence  of  which  its  chloro- 
phyl  prepares  the  atmosphere  for  animals  by  the  removal  of 
carbonic  anhydride  and  the  addition  of  oxygen,  while  for 
Torula  neither  this  gas  nor  sunlight  is  essential. 

Moreover,  the  fungus  (Tcmda)  demands  a  higher  kind  of 
food,  one  more  nearly  related  to  tiie  pabulum  of  animals;  and 
is  absolutely  independent  of  sunlight,  if  not  actually  injured 
by  it ;  not  to  mention  the  remarkable  process  of  fermentation. 


UNIOELLAB  ANQUJA 
The  Pboteus  Animalcule  (AmcAa). 

In  order  to  illustrate  animal  life  in  its  simpler  form  we 
choose  the  above-named  creature,  which  is  nearly  as  readily 
obtainable  as  Protococcus  and  often  under  the  same  circum- 
stances. 

MorpihiologlflaL — Amaba  is  a  microscopic  mass  of  transparent 
protopla«n,  about  the  size  of  the  largest  of  the  colorless  blood- 
corpuscles  of  cold-blooded  animals,  with  a  clearer,  more  con- 
sistent outer  zone  {edomrc),  (although  without  any  proper  cell 
wall),  and  a  more  fluid,  granular  inner  part.  A  clear  space 
{eontractUe  veaide,  vacuole)  makes  its  appearance  at  intervals  in 
the  ectosarc,  which  may  disappear  somewhat  suddenly.  This 
appearance  and  vanishing  have  suggested  the  term  pulsating 
or  contracting  vesicle.  Both  a  nucleus  and  nucleolus  may  be 
seen  in  Amoeba.  At  varying  short  periods  certain  parts  of  its 
body  (paeudopodia)  are  thrust  out  and  others  withdrawn. 

ThyilologioaL— Amoeba  can  not  live  on  such  food  as  proves 
adequate  for  either  Protococcus  or  Twula,  but  requires,  besides 


';'-Hi^'^'i'i'1^'W"'^V--*R:^(f4'' 


>^,3i*;?t!^j^^^8^'*^i^i^2^.^^.«'*«E^i^'*i^^ 


ill  wall;  or 
lotile  form, 
lulose  coat, 
;ate  again. 
nrly  animal 

in  common 
irtue  of  be- 
aterial  into 
le  by  analo-  ^ 

>  the  green 
L  its  cfaloro* 
removal  of 
,  while  for 

ler  kind  of 
limals;  and 
illy  injured 
mentation. 


er  form  we 
r  as  readily 
^me  circum* 

transparent 
>rless  blood- 
r,  more  con- 
■  proper  cell 
clear  space 
intervals  in 
enly.  This 
m  pulsating 
>lus  may  be 
L  parts  of  its 
drawn, 
od  as  proves 
ires,  besides 


UNIOBLLAB  ANIMALS.  18 

inorganic  and  unorgani^  food,  also  organized  matter  in  the 
form  of  a  complex  organic  compound  known  as  protetn,  which 


ne 


Wn.9. 


■teM. 


ve-, 


Fw.ll. 


na.ll. 


fte.U. 


■ne. 


-re 


fte. 


ire 


Fie.  14. 


fto.ia. 


FM.lfc 


Fhm. 


ptotrading  to  form  •  pwndopodiam,  into 


drawn  wider  zA»,  D.  8.)      ^     ^    .        .. 
Fw.  8.-1110  kKsomotor  phMB ;  tboectoplHm  ia 

Fu..t?fA^i:ir'^sruSss:iph-a  a  tog«t-rtoor««ta^  am.  ««««««-« 

ItoflS^I«*tto« of  U.0 of«rtuw «i«.«rtod ta Fig.  9 .ftor oo«i*eto li«^ 
of  tbBtagMted  orgMdu  M»  luuioMBted  nudorgoliig  ojeeuon  ( 


i(«nsretloii)*t/)>,iB 


^%S;:!^ssz:^sss:^^t^^s^ 


In  tha  above 
dinm;  M, 


,.„of  tiMianw  indlTld- 

.»»r    .i-u.™>»«.~™,.-i.  Wthat^bonnctooadlTldaaftMt. 
dS5iiS^SS5«*tatv;«»oto;a«.tliomiclaQa:  pt.  paoudopo- 
food-partlrle. 


contains  nitrogen  in  addition  to  carbon,  hydrogen,  and  oxygen. 
In  fact.  Amoeba  can  prey  upon  both  plants  and  animals,  and 
thus  use  up  as  food  protoplasm  itself.    The  pseudopodia  serve 
the  double  purpose  of  organs  of  locomotion  and  prehension. 
This  creature  absorbs  oxygen  and  evolves  carbon  dioxide. 


u 


ANIMAL  PHTSIOLOOT. 


Inasmnch  as  any  part  of  the  body  may  serre  for  the  admission, 
and  possibly  the  digestion,  of  food  and  the  ejection  of  the  use- 
less remains,  we  are  not  able  to  define  the  functions  of  special 
parts.  Amoeba  exercises,  however,  some  degree  of  choice  as  to 
what  it  accepts  or  rejects. 

The  movements  of  the  pseudopodia  cease  when  the  tempera- 
ture of  the  surrounding  medium  is  raised  or  lowered  beyond  a 
certain  point.  It  can,  however,  survive  in  a  quiescent  form 
greater  depression  than  elevation  of  the  temperature.  Thus,  at 
35°  0.,  heat-rigor  is  induced ;  at  40°  to  45°  0.,  death  results ;  but 
though  all  movement  is  arrested  at  the  freezing-point  of  water, 
recovery  ensues  if  the  temperature  be  gradually  raised.  Its 
form  is  modified  by  electric  shocks  and  chemical  agents,  as  well 
as  by  variations  in  the  temperature.  At  the  present  time  it  is 
not  possible  to  define  accurately  the  functions  of  the  vacuoles 
found  in  any  of  the  organisms  thus  far  considered.  It  is 
worthy  of  note  that  Amoeba  may  spontaneously  assume  a 
spherical  form,  secrete  a  structureless  covering,  and  remain  in 
this  condition  for  a  variable  period,  reminding  us  of  the  similar 
oehavior  of  Torula. 

Amoeba  reproduces  by  fission,  in  which  the  nucleus  takes  a 
prominent  if  not  a  directive  part,  as  seems  likely  it  does  in  re- 
gard to  all  the  functions  of  unicellular  organisms. 

OonoluUnuL— It  is  evident  that  Amoeba  is,  in  much  of  its  be- 
havior, closely  related  to  both  colored  and  colorless  one-celled 
plants.  All  of  the  three  classes  of  organisms  are  composed  of 
protoplasm ;  each  can  construct  protoplasm  out  of  that  which  is 
very  different  from  it ;  each  builds  up  the  inanimate  inorganic 
world  into  itself  by  virtue  of  that  force  which  we  call  vital,  but 
which  in  its  essence  we  do  not  understand ;  each  multiplies  by 
division  of  itself,  and  all  can  only  live,  move,  and  have  their 
being  under  certain  definite  limitations.  But  even  among 
forms  of  life  so  lowly  as  those  we  have  been  considering,  the 
differences  between  the  animal  and  vegetable  worlds  appear. 
Thus,  Amoeba  never  has  a  cellulose  wall,  and  can  not  subsiH 
on  inorganic  food  alone.  The  cellulose  wall  is  not,  however, 
invariably  present  in  plants,  though  this  is  generally  the  case ; 
»ud  there  are  animals  (Ascidians)  with  a  cellulose  investment. 
Such  are  very  exceptional  oases.  But  the  law  that  animals 
must  have  organized  material  {protein)  as  food  is  without  ex- 
ception, and  forms  a  broad  line  of  distinction  between  the  ani- 
mal and  vegetable  kingdoms. 

Amoeba  will  receive  further  consideration  later;  in  the 


PASAEOnO  OBOANISM& 


16 


admission, 
the  use* 
of  special 
loice  as  to 

tempera- 

beyond  a 

cent  form 

Thus,  at 

«ults;  but 

t  of  water, 

aised.    Its 

its,  as  well 

t  time  it  is 

le  vacuoles 

red.     It  is 

assume  a 

remain  in 

the  similar 

us  takes  a 
does  in  re- 

h  of  its  be* 
}  one-celled 
omposedof 
at  which  is 
e  inorganic 
11  vital,  but 
iltiplies  by 
have  their 
ren  among 
dering,  the 
ids  appear, 
not  subsi.'^t 
b,  however, 
iy  the  case ; 
nvestment. 
at  animals 
irithout  ex* 
len  the  ani* 

er;  in  the 


mean  time,  we  turn  to  the  study  of  forms  of  life  in  many  respects 
intermediate  between  plants  and  animals,  and  full  of  practical 
interest  for  mankind,  on  account  of  their  relations  to  disease, 
as  revealed  by  recent  investigations. 


PABASmO  OBGANISMB. 

The  Fungi. 
Molds  (Feniomium  Olatusum  and  Mucor  Mucedo). 

Closely  related  to  IbruJa  physiologically,  but  of  more  com* 
plex  structure,  are  the  molds,  of  which  we  select  for  convenient 
study  the  common  green  mold  (PeniciUium),  found  growing  in 
dark  and  moist  places  on  bread  and  similar  substances,  and  the 
white  mold  (Mucor),  which  grows  readily  on  manure. 

The  fungi  originate  in  spores,  which  are  essentially  like 
Torula  in  structure,  by  a  process  of  budding  and  longitudinal 
extension,  resulting  in  the  formation  of  transparent  branches 
or  tubules,  filled  with  protoplasm  and  invested  by  cellulose 
walls,  across  which  transverse  partitions  are  found  at  regular 
intervals,  and  in  which  vacuoles  are  also  visible. 

The  spores,  when  growing  thus  in  a  liquid,  give  rise  to  up- 
ward branches  (aMrud  hyphce),  and  downward  branches  or  root* 
lets  {submerged  hypluz).  These  multitudinous  branches  inter- 
lace in  every  direction,  forming  an  intricate  f elt*work,  which 
supports  the  green  powder  (spores)  which  may  be  so  easily 
shaken  oft  from  a  growing  mold.  In  certain  cases  the  aSrial 
hyphflB  terminate  in  tufts  of  branches,  which,  by  transverse 
division,  become  split  up  into  spores  {Conidia),  each  of  which 
is  similar  in  structure  to  a  yeast-celL 

The  green  coloring  matter  of  the  fungi  is  not  chlorophyl. 
The  Oonidia  germinate  under  the  same  conditions  as  Torula. 

Mmot  Mnoado.— The  growth  and  development  of  this  mold 
may  be  studied  by  simply  inverting  a  glass  tumbler  over  some 
horse-dung  on  a  saucer,  into  which  a  very  little  water  has 
been  poured,  and  keeping  the  preparation  in  a  warm  place. 

Very  soon  whitish  filaments,  gradually  getting  stronger,  ap* 
pear,  and  are  finally  topped  by  rounded  heads  or  spore-cases 
{Sporangia).  These  filaments  are  the  hyphat,  similar  in  struct- 
ure to  those  of  Penioillium.  The  spore-case  is  filled  with  a 
multitude  of  oval  bodies  {spores),  resulting  from  the  subdivis- 
ion of  the  protoplasm,  which  are  finally  released  by  the  spore* 


{ 


VNkflT< 


*At**»«iS*iMaw«i»swwsp®i 


PABASITIC  ORGANISMS, 


17 


FHs.  17  to  ttb— III  the  ftdlowiiiK  flfiuca.  fto.  denotN  aMal  byptm :  «p,  i 
goapore;  «v, exoaporium ;  mjrjnjroeliiiin ;  mc, maeHage ;  el,coluiiiell 

Flo.  n.—Spa»hemrlDS  hTPlxB  of  ■ooor.  Krowinc  from  hcmwduiur. 

no.  18.-TKe  MUM,  tCMed  out  wllh  needlM  (A,  4). 

Fioa.  I>,  W,  •!.— SueoMrive  alagM  In  the  devektpawBt  of  ttw  qionuiffiam. 

Flo.  n.— iMlated  ■MTM  of  IbMar. 

Fw.  at.— GcmiliMttiic  ipaTCa  ol  tba  Mine  mold. 

Fm.  M.-aaeaMrive  MfM  In  the  germination  of  •  rinRle  epore. 

Fiaa.  K,  M,  t7.— fliioewl¥»  r*- •- ""^ ' 

Flo.  M.— OueeemlTe  itagea  oL. 
eilUum  In  an  ohJaoHElnM  < 


»  phaam  In  the  oonJngatlTe  nroMM  of  Muoor. 

ovaarved  daring  ten  boon  In  the  growth  of  a  oonMlophare  of  ftni- 

«oaltara(D,^ 


./ 


rm.m. 


case  becoming  thinned  to  the  point  of  rupture.  The  devel- 
opment of  these  spores  takes  place  in  substantially  the  same 
manner  as  those  of  Penicillium.  Sporangia  developing  spores 
in  this  fashion  by  division  of  the  protoplasm  are  termed  asci, 
tOid  the  spores  cueosporea. 

So  long  as  nourishment  is  abundant  and  the  medium  of 
growth  fluid,  this  asexual  method  of  reproduction  is  the  only 
one ;  but,  under  other  circumstances,  a  mode  of  increase,  known 
as  cor^jiigation,  arises.  Two  adjacent  hyph»  enlarge  at  the  ex- 
tremities into  somewhat  globular  heads,  bend  over  toward  each 
other,  and,  meeting,  their  opposed  faces  become  thinned,  and 
the  contents  intermingle.  Tbe  result  of  this  union  {zygospore) 
undergoes  now  certain  further  changes,  the  cellulose  coat  being 
separated  into  two— an  outer,  darker  in  color  {exoeporiutn),  and 
an  inner  colorless  one  {endo^oorivm). 

Under  favoring  circumstances  these  coats  burst,  and  a 
branch  sprouts  forth  from  which  a  vertical  tube  arises  that 
termiimtes  in  a  sporangium,  in  which  spores  arise,  as  before  de- 
scribed. It  will  be  apparent  that  we  have  in  Mucor  the  exem- 
plification of  what  is  known  in  biology  as  "dUemcUion  of  gen- 
erations" — ^that  is,  there  is  an  intermediate  generation  be- 
tween the  original  form  and  that  in  which  tiie  original  is 
again  reached. 

Physiologically  the  molds  closely  resemble  yeast,  some  of 
them,  as  Muoor,  being  capable  of  exciting  a  fermentation. 

The  ftmgi  are  of  special  interest  to  the  medical  student,  be- 
cause many  forms  of  cutaneous  disease  are  directly  associated 
with  their  growth  in  the  epithelium  of  the  skin,  as,  for  exam- 
ple, common  ringworm ;  and  their  great  vitality,  and  the  facil- 
ity with  which  their  spores  are  widely  dispersed,  explain  the 
highly  contagious  nature  of  such  diseases.  The  media  on  which 
they  flourish  (feed)  indicates  their  great  physiological  differ- 
ences in  this  particular  from  the  green  plants  proper.  They  are 
closely  related  in  not  a  few  respects  to  an  important  class  of 
vegetable  organisms,  known  as  bacteria,  to  be  considered  forth- 
with. 

I 


■■wii 


I 


18 


animal  physiology. 
The  Bacteria. 


The  bacteria  include  numberless  varieties  of  organisms  of 
extreme  minuteness,  many  of  them  visible  only  by  the  help  of 
the  most  powerful  lenses.  Their  size  has  been  estimated  at 
from  tvhnf  to  ttW  of  an  inch  in  diameter. 

They  grow  mostly  in  the  longitudinal  direction,  and  repro- 
duce by  transverse  division,  forming  spores  from  which  new 
generations  arise. 

Some  of  them  have  vibratile  cilia,  while  the  cause  of  the 
movements  of  others  is  quite  unknown. 

As  in  many»other  lowly  forms  of  life,  there  is  a  quiescent 
as  well  as  an  active  stage.    In  this  stage  {zoogUm  fonn)  they 


,-» 


« 


Fio.». 


f*  '^\ 


no.ao. 


no.  SI. 


tra.ai 


Ito.  «>.-lUoraoocous,  v«7  Uka  a  ifwra,  but  uMAlljr  much  nwllw. 

•to'  U -BS^wT'Tlie  omtml  flUment  praMiitMl  thi«  wniMitad  WMnaee  m  tto  twuU  of 
no.  Mr-eMriUimi ;  TMrlow  tomw.  Tta  flnt  two  repnatnt  vtbrio,  whfcfli  Is  poHiiiiy  omr  • 
na.%!f£$!A  MrfM.  Mwrn,  ihowtiW  »  qrfrilhun  •«gri|irt«  in  tte 

are  surrounded  by  a  gelatinous  matter,  probably  secreted  by 
themselves. 


MP 


rganisms  of 
the  help  of 
stimated  at 

,  and  repro- 
which  new 

ause  of  the 

a  quiescent 
form)  they 


10.  Ml 


nee  M  tto  TWuU  of 

km. 

Is  poHililj  onlr  • 

Mtlncitate. 

'  seoreted  by 


PARASITIC  ORGANISMS. 


19 


Bacteria  grow  and  reproduce  in  Pasteur's  solution,  render- 
ing it  opaque,  as  well  as  in  almost  all  fluids  that  abound  in 
proteid  matter.  That  such  fluids  readily  putrefy  is  owing  to 
the  presence  of  bacteria,  the  vital  action  of  which  suffices  to 
break  asunder  complex  chemical  compounds  and  produce  new 
ones.  Some  of  the  bacteria  reqture  oxygen,  as  BaciUus  cm- 
tkracis,  while  others  do  not,  as  the  organism  of  putrefaction. 
Bacterium  termo. 

Bacteria  are  not  so  sensitive  to  slight  variations  in  tempera- 
ture as  most  other  organisms.  They  can,  many  of  them,  with- 
stand freezing  and  high  temperatures.  All  bacteria  and  all 
germs  of  bacteria  are  killed  by  boiling  water,  though  the  spores 
are  much  more  resistant  than  the  mature  organisms  themselves. 
Some  spores  can  resist  a  dry  heat  of  140"  C. 

The  spores,  like  Torula  and  Protococcus,  bear  drying,  with- 
out loss  of  vitality,  for  considerable  periods. 

That  different  groups  of  bacteria  have  a  somewhat  different 
life-history  is  evident  from  the  fact  that  the  presence  of  one 
checks  the  other  in  the  same  fluid,  and  that  successive  swarms 
of  different  kinds  may  flourish  where  others  have  ceased  to 
live. 

That  these  organisms  are  enemies  of  the  constituent  cells  of 
the  tissues  of  the  highest  mammals  has  now  been  abundantly 
demonstrated.  That  they  interfere  with  the  normal  working 
of  the  organism  in  a  great  variety  of  ways  is  also  clear;  and 
certain  it  is  that  the  harm  they  do  leads  to  aberration  in  cell- 
life,  however  that  may  be  manifested.  They  rob  the  tissues  of 
their  nutriment  and  oxygen,  and  poison  them  by  the  products 
of  the  decompositions  they  produce.  But  apart  from  this,  their 
very  presence  as  foreign  agents  must  hamper  and  derange  the 
delicate  mechanism  of  cell-life. 

These  organisms  seem  to  people  the  air,  land,  and  waters 
with  invisible  hosts  far  more  numerous  than  the  forms  of  life 
we  behold.  Fortunately,  they  are  not  all  dangerous  to  the 
higher  forms  of  mammalian  life ;  but  that  a  large  proportion 
of  the  diseases  which  afflict  both  man  and  the  domestic  animals 
are  directly  caused,  in  the  sense  of  being  invariably  associated 
with,  the  presence  of  such  forms  of  life,  is  now  beyond  doubt. 

The  facts  stated  above  explain  why  that  should  be  so ;  why 
certain  maladies  should  be  infectious ;  how  the  germs  of  dis- 
ease may  be  transported  to  a  friend  wrapped  up  in  the  folds  of 
a  letter. 

Disease  thus  caused,  it  must  not  be  forgotten,  is  an  illustra- 


wm 


30 


ANIMAL  PHTSIOLOOT. 


tion  of  the  struggle  for  existence  and  the  sarvival  of  the  fittest, 
(if  the  cells  of  an  organism  are  mightier  than  the  bacteria,  the 
latter  are  overwhelmed;  but  if  the  bacteria  are  too  great  in 
numbers  or  more  vigorous,  the  cells  must  yield ;  the  battle  may 
waver — now  dangerous  disease,  now  improvement — ^but  in  the 
end  the  strongest  in  this,  as  in  other  instances,  prevail 


UNICELLULAB  AJUDtAlS  WITH  DIFFERENTIATION  OF 

STRUCTDBE. 

The  Bell- Animalcule  iVorticeUa). 

Amoeba  is  an  example  of  a  one-celled  animal  with  little  per- 
ceptible differentiation  of  structure  or  corresponding  division 
of  physiological  labor.  This  is  not,  however,  the  case  with  all 
unicellular  animals,  and  we  proceed  to  study  one  of  these  with 
considerable  development  of  both.  The  Bell -animalcule  is 
found  in  both  fresh  and  salt  water,  either  single  or  in  groups. 
It  is  anchored  to  some  object  by  a  rope-like  stalk  of  clear  pro- 
toplasm, that  has  a  spiral  appearance  when  contracted;  and 
which,  with  a  certain  degree  of  regularity,  shortens  and  length- 
ens alternately,  suggesting  that  more  definite  movement  (con- 
traction) of  the  form  of  protoplasm  known  as  muscle,  to  be 
studiv  >i  later. 

The  body  of  the  creaturais  bell-shaped,  hence  its  name ;  the 
bell  being  provided  with  a  thick  everted  lip  (peristome),  covered 
with  bristle-like  extensions  of  the  protoplasm  (ct2ta),  which  are 
in  almost  constant  rhythmical  motion.  Covering  the  mouth  of 
the  bell  is  a  lid,  attached  by  a  hinge  r  f  protoplasm  to  the  body, 
which  may  be  raised  or  lowered.  A  wide,  funnel-like  depres- 
sion (cesophagus)  leads  into  the  softer  substance  within  which 
it  ends  blindly.  The  outer  part  of  the  animal  {euUcula)  is 
denser  and  more  transparent  than  any  other  part  of  the  whole 
creature ;  next  to  this  is  a  portion  more  granular  and  of  inter- 
mediate transparency  between  the  external  and  innermost 
portions  (cortical  layer).  Below  the  disk  is  a  space  (contractile 
vesicle)  filled  with  a  thin,  clear  fluid,  which  may  bo  seen  to 
enlarge  slowly  and  then  to  collapse  suddenly.  When  the  Vorti- 
cella  is  feeding,  these  vesicles  may  contain  food-particles,  and 
in  the  former,  apparently,  digestion  goes  on.  Such  food  vacu- 
oles (vesicles)  may  circulate  up  one  side  of  the  body  of  the  ani- 
mal and  down  the  other.  Their  exact  significance  is  not  known, 
but  it  would  appear  as  if  digestion  went  on  within  them ;  and 


•i*r/*W«v^v■j«^lWS4-~^'S^5I3Ea5»*Sii55«^^ 


F  the  fittest 
octeria,  the 

00  great  in 

1  battle  may 
-but  in  the 
aiL 


ltion  op 


bh  little  per- 
ing  division 
3ase  with  all 
►f  these  with 
umalcule  is 
)r  in  groups, 
of  clear  pro- 
tracted; and 
\  and  length- 
vement  (con- 
misde,  to  be 

ts  name ;  the 
yme),  covered 
a),  which  are 
the  mouth  of 
I  to  the  body, 
1-like  depres- 
within  which 
{(BtUieula)  is 
of  the  whole 
and  of  inter- 
id  innermost 
ce  (cow^racftk 
ly  bo  seen  to 
den  the  Vorti- 
particles,  and 
Lch  food  vacu- 
idy  of  the  ani- 
ls not  known, 
lin  them ;  and 


U5ICELLULAB  ANIMALS. 


SI 


possibly  the  clear  fluid  with  which  they  are  filled  may  be  a  spe- 
cial secretion  with  solvent  action  on  food. 


trs 


fta.«r. 


na.8B. 


no.  as. 


noa  »4to40.-ln  the  t««owtog  .flgurw  Atewtesdhe, 
?iJ8^rw^\eSnmlej«/,  oontwrtUe  ifter  ;   c. 


at ;  iM,  nuolMia ;  ^^olUmii 


of  TMtiaellte  'diowliig  the  crMtnre  in 


FioX^SteSSnTto  thewttMided  Md  to  the  retrmcted 

•late.    (SurfMe  Tiewe.).  .    ..     _  .    .  ._„.^ 

Fia.  w!-8how«  food-vMuolea ;  one  to  the  act  of  tagefr 

Fio-^w"- A  Tortloelto,  to  whidi  the  prooees  of  mulUpUca- 
K«.1S^''lh?!SSl&  W-on ;  the  production  of  two  to- 
r,«l5lffiJ.'SS?S?f5^«ctlonhyco«]«girtlan. 
Fio.  40.— An  enoyirted  TorfierlU. 


no.aa. 


Situated  somewhat  centrally  is  a  horseshoe-shaped  body, 
with  well-defined  edges,  which  stains  more  readily  than  the  rest 
of  the  cell,  indicating  a  different  chemicaLcomposition ;  and, 
from  the  prominent  part  it  takes  in  the  reproductive  and  other 
functions  of  the  creature,  it  may  be  considered  the  nucleus 

Multiplication  of  the  species  is  either  by  gemiwaton  or  by 
fission.  In  the  first  case  the  nucleus  divides  and  the  fragments 
are  transformed  into  locomotive  germs ;  in  the  latter  the  entire 
animal,  including  the  nucleus,  divides  longitudinally,  each  half 
becoming  a  similar  complete,  independent  organism.    Still  an- 


jtt  ANIMAL  PHT8IOL0OY. 

other  method  of  reproduction  is  known.  A  more  or  less  globu- 
lar body  encircled  with  a  ring  of  cilia  and  of  relatively  small 
size  may  sometimes  be  seen  attached  to  the  usual  form  of  Vorti- 
cella,  with  which  it  finally  becomes  blended  into  one  mass.  This 
seems  to  foreshadow  the ''  sexual  conjugation  **  of  higher  forms, 
and  is  of  great  biological  significance. 

Vorticella  may  pass  into  an  encysted  and  quiescent  stage  for 
an  indefinite  period  and  again  become  active.  The  history  of 
the  Bell-animalcule  is  substantially  that  of  a  vast  variety  of 
one-celled  organisms  known  as  Infusoria,  to  which  Amoeba 
itself  belongs.  It  will  be  observed  that  the  resemblance  of  this 
organism  to  Amceba  is  very  great ;  it  is,  however,  introduced 
here  to  illustrate  an  advance  in  differentiation  of  structure ;  and 
to  show  how,  with  the  latter,  there  is  usually  a  physiological 
advance  also,  since  there  is  additional  functional  progress  or 
division  of  labor;  but  still  the  whole  of  the  work  is  done  with- 
in one  cell.  Amoeba  and  Vorticella  are  both  factories  in  which 
all  of  the  work  is  done  in  one  room,  but  in  the  latter  case  the 
machinery  is  more  complex  than  in  the  former ;  there  are  cor- 
respondingly more  processes,  and  each  is  performed  with  greater 
perfection.  Thus,  food  in  the  case  of  the  Boll-animalcule  is 
swept  into  the  gullet  by  the  currents  set  up  by  the  multitudes 
of  vibrating  arms  around  this  opening  and  its  immediate  neigh- 
borhood ;  the  contractile  vesicles  play  a  more  prominent  part ; 
and  the  waste  of  undigested  food  is  ejected  at  a  more  definite 
portion  of  the  body,  the  floor  of  the  oesophagus ;  while  all  the 
movements  of  the  animal  are  rhythmical  to  a  degree  not  exem- 
plified in  such  simple  forms  as  Amoeba;  not  to  mention  its 
various  resources  for  multiplication  and,  therefore,  for  its 
perpetuation  and  permanence  as  a  species.  It,  too,  like  all  the 
unicellular  organisms  we  have  been  considering,  is  susceptible 
of  very  wide  distribution,  being  capable  of  retaining  vitality  in 
the  dried  state,  so  that  these  infusoria  may  be  carried  in  vari- 
ous directions  by  winds  in  the  form  of  microscopip  dust. 


MULTIOELLULAB  OBOANISMB. 

Thb  Fbbsh-Watbr  P0LTP8  {Hydra  viridia ;  Hydra  fuaoa). 

The  comparison  of  an  animal  so  simple  in  structure,  though 
made  up  of  many  cells,  as  the  Polyp,  with  the  more  complex 
organizations  with  which  we  shall  have  especially  to  deal,  may 


"mm 


MULTICELLULAR  ORGANISMS. 


98 


globn- 
vely  small 
1  of  Vorti- 
lass.  This 
her  forms, 

t  stage  for 
history  of 
variety  of 
Amoeba 
mce  of  this ' 
introduced 
icture ;  and 
ysiological 
»rogres8  or 
done  with- 
« in  which 
er  case  the 
re  are  cor- 
rith  greater 
imalcule  is 
multitudes 
iate  neigh- 
linent  part ; 
ore  definite 
hile  all  the 
e  not  exem- 
mention  its 
>re,  for  its 
like  all  the 
susceptible 
;  vitality  in 
led  in  vari- 
lust. 


dra  fuaca). 

ure,  though 
>re  complex 
»  deal,  may 


be  fitly  undertaken  at  this  stage.  The  Polyps  are  easily  obtain- 
able from  ponds  in  which  they  are  found  attached  to  various 
kinds  of  weeds.  To  the  naked  eye,  they  resemble  translucent 
masses  of  jelly  with  a  greenish  or  reddish  tinge.  They  range 
in  size  from  one  quarter  to  one  half  an  inch ;  are  of  an  elongated 
cylindrical  form ;  provided  at  the  oral  extremity  with  thread- 
like tentacles  of  considerable  length,  which  are  slowly  moved 
about  in  all  directions ;  but  they  and  the  entire  body  may  short- 
en rapidly  into  a  globular  mass.  They  are  usually  attached  at 
the  opposite  (aboral)  pole  to  some  object,  but  may  float  free,  or 
slowly  crawl  from  place  to  place.  It  may  be  observed,  under 
the  microscope,  that  the  tentacles  now  and  then  embrace  some 
living  object,  convey  it  toward  an  opening  (mouth)  near  their 
base,  from  which,  from  time  to  time,  refuse  material  is  cast  out. 
It  may  be  noticed,  too,  that  a  living  object  within  the  touch  of 
these  tentacles  soon  loses  the  power  to  struggle,  which  is  owing 
to  the  peculiar  cells  (netUe-ceUs,  \vrticaHng  capsules,  nemato- 
cysts)  with  which  they  are  abundantly  provided,  and  which  se- 
crete a  poisonous  fluid  that  paralyzes  prey. 

The  mouth  leads  into  a  simple  cavity  (ccelom)  in  which 
digestion  proceeds.  The  green  color  in  Hydra  viridis,  and  the 
red  color  of  Hydra  f  usca,  is  owing  to  the  presence  of  cidorophyl, 
the  function  of  which  is  not  known.  Hydra  is  structurally  a 
sac,  made  up  of  two  layers  of  cells,  an  outer  (ectoderm)  and 
an  inner  {endoderm) ;  the  tentacles  being  repetitions  of  the 
structure  of  the  main  body  of  the  animal,  and  so  hollow  and 
composed  of  two  cell  layers.  Speaking  generally,  the  outer 
layer  is  devoted  to  obtaining  information  of  the  surroundings ; 
the  inner  to  the  work  of  preparing  nutriment,  and  probably, 
also,  discharging  waste  matters,  in  which  latter  assistance  is 
also  received  from  the  outer  layer.  As  digestion  takes  place 
largely  within  the  cells  themselves,  or  is  intracellular,  we  are 
reminded  of  Yorticella  and  still  more  of  Amoeba.  There  is  in 
Hydra  a  genfral  advance  in  development,  but  not  very  much  in- 
dividual cell  specialization.  That  of  the  ucticating  capsules  is 
one  of  the  best  examples  of  such  specialization  in  this  creature. 
(X  Polyp  is  like  a  colony  of  Amoebee  in  which  some  division  of 
utbor  (function)  has  taken  place ;  a  sort  of  biological  state  in 
which  every  individual  is  nearly  equal  to  his  neighbor,  but 
somewhat  more  advanced  than  those  neighbors  not  members  of 
the  organization. 

But  in  one  respect  the  Polyps  show  an  enormous  advance. 
Ordinarily  when  nourishment  is  abundant  hydra  multiplies  by 


MULTlOBfJiULAB  OROANISMa 


S6 


'O 


ito.A 


Fi<Mi  41  to  46.— In  Um  followtaic  flguna,  ee,  dMtotaaaclodMin ;  «it,  endoderm ;  t,  tratacle ;  kp, 

hnmitoiiie ;  /,  foot ;  («,  twtw :  ov,  ovarjr ;  jm,  pMudopodlum  ;  ee',  iaiKer  ectoderm-ceUs ; 

ne',  larger  neiiMUMnraU  before  rupture ;  cip,  Kleioenberg'e  flben ;  ct,  eupimrtins  Uinella ; 

d,  chloropli]rl*faniuiv  hndlet ;  c,  oUlum 
na.  41.— The  green  hjrdrs,  at  the  nuulmum  of  oontractkm  and  elongation  of  ita  bodj.   The 

creature  is  reprcaented  In  the  act  of  wislnir  a  nnali  cmataoean  (A,  t\. 
Fia.  4*.- Traavrene  aectkw  aeroaa  the  bodjr  of  a  hjdra,  in  the  dlgeettve  carl^  of  which  a 

Mnall  cmataoean  Is  repwsented. 
Fio.  4».-The  IwadiM  typea  of  thread-cells,  aftw  MberatioB  from  the  body  (F.  8).   Theodlsare 

repreaented  in  tfie  active  and  the  resting  ooaditions ;  in  the  former  all  the  parts  are  more 

distlnctljr  seen  In  eoaaeiineooe  of  the  neeeaMiy  e>f  isloii 
Fio.  44.— Small  portion  of  a  transverse  section  aeroas  tlie  bodjr  of  a  green  hydra  (D,  S). 
Flo.  46.— A  large  brown  hydra  bearing  at  the  same  time  bods  produced  aaezually  and  sexual 

Fia.4E^Liwger  crik  of  the  ectodHrm  Isolated.    Note  the  prociwsss  of  the  cells  or  Klelnen- 

beiK's  fibers.    (F,  8.) 
An  of  the  cuts  on  pages,  •,  11,  IS,  IS,  18, 81  and  81, have  been  seieoted  fhim  Howes'  "AUaa  of 

Biology." 

budding,  and  when  out  into  portions  each  may  become  a  com- 
plete individual.  However,  under  other  circumstances,  near 
the  bases  of  the  tentacles  the  body  wall  may  protrude  into  little 
masses  if^esiea),  in  which  cells  of  peculiar  formation  {Bperma- 
tozoa)  arise,  and  are  eventually  set  free  and  unite  with  a  cell 
{ovum)  formed  in  a  similar  protrusion  of  larger  size  {ovary). 
iHere,  then,  is  the  first  instance  in  which  distinctly  sexual  re- 
production has  been  met  in  our  studies  of  the  lower  forms  of 
life.  This  is  substantially  the  same  process  in  Hydra  as  in 
mammals.  But,  as  both  male  and  female  cells  are  produced  by 
the  same  individual,  the. sexes  are  united  {hermapJiroditiam) ; 
each  is  at  once  male  and  female. 

f  Any  one  watching  the  movements  of  a  Polyp,  and  compar- 
inglt  with  those  of  a  Bell-animalcule,  will  observe  that  the 
former  are  much  less  machine-like ;  have  greater  range ;  seem 
to  be  the  result  of  a  more  deliberate  choice ;  are  better  adapted 
to  the  environment,  and  calculated  to  achieve  higher  ends.  In 
the  absence  of  a  nervous  system  it  is.not  easy  to  explain  how 
one  part  moves  in  harmony  with  another,  except  by  that  process 
which  seems  to  be  of  such  wide  application  in  nature,  adapta- 
tion from  habitual  simultaneous  effects  on  a  protoplasm  capable 
of  responding  to  stimuli  When  one  process  of  an  Amoeba  is 
touched,  it  is  likely  to  withdraw  all.  This  we  take  to  to  be  due 
to  influences  radiating  through  molecular  movement  to  other 
parts;  the  same  principle  of  action  may  be. extended  to  Hydra. 
vThe  oftener  any  molecular  movement  is  repeated,  the  more  it 
(tends  to  become  organised  into  regularity,  to  become  fixed  in 
^its  mode  of  action ;  and  if  we  are  not  mistaken  this  is  a  funda- 
mental law  throughout  the  entire  world  of  living  things,  if  not 
W  all  things  animate  and  inanimate  alike.  To  this  law  we 
^shall  return. 

\|ti!it  Hydra  is  a -creature  of  but  very  limited  specializations; 
there  are  neither  organs  of  circulation,  respiration,  nor  excretion. 


96 


ANIMAL  PHYSIOLOGY. 


if  we  exclude  the  doubtful  case  of  the  thread-cells  {urticafing 
capsvlea).  The  animal  breathes  by  the  entire  surface  of  the 
body ;  nourishment  passes  from  cell  to  cell,  and  waste  is  dis- 
charged into  the  water  surrounding  the  creature  from  all  cells, 
though  probably  not  quite  equally.  All  parts  are  not  digestive, 
respiratory  etc.,  to  the  same  degree,  and  herein  does  it  differ 
greatly  from  Amoeba  or  even  Vorticella,  though  fuller  knowl- 
edge will  likely  modify  our  views  of  the  latter  two  and  similar 
organisms  in  this  regfurd. 


THB  CELL  REiCONSIDERED. 

Having  now  studied  certain  one-celled  plants  and  animals, 
and  some  very  simple  combinations  of  cells  (molds,  etc.),  it  will 
be  profitable  to  endeavor  to  generalize  the  lessons  these  humble 
organisms  convey ;  for,  as  will  be  constantly  seen  in  the  study 
of  the  higher  forms  of  life  of  which  this  work  proposes  to  treat 
principally,  the  same  laws  operate  as  in  the  lowliest  living 
creatures.  The  most  complex  organism  is  made  up  of  tissues, 
which  are  but  cells  and  their  products,  as  houses  are  made  of 
bricks,  mortar,  wood,  and  a  few  other  materials,  however  large 
or  elaborate. 

The  student  of  physiology  who  proceeds  scientifically  must 
endeavor,  in  investigating  the  functions  of  each  organ,  to  learn 
the  exact  behavior  of  each  cell  as  determined  by  its  own  inher- 
ent tendencies,  and  modified  by  the  action  of  neighboring  cells. 
The  reason  why  the  function  of  one  organ  differs  from  that  of 
another  is  that  its  cells  have  departed  in  a  special  direction 
from  those  properties  common  to  all  cells,  or  have  become  func- 
tionally differentiated.  But  such  a  statement  has  no  meaning 
unless  it  be  well  understood  that  cells  have  certain  properties  in 
common.  This  is  one  of  the  lessons  imparted  by  the  preceding 
studies  which  we  now  review.  Briefly  stated  in  language  now 
extensively  used  in  works  on  biology,  the  common  properties  of 
cells  (protoplasm),  whether  animal  or  vegetable,  whether  con- 
stituting in  themselves  entire  animals  or  plants,  or  forming  the 
elements  of  tissues,  are  these :  The  collective  chemical  processes 
associated  with  the  vital  activities  of  cells  are  termed  its  meta- 
bolism. Metabolism  is  constructive  when  more  complex  com- 
pounds are  formed  from  simpler  ones,  as  when  the  Protococcus- 
cell  builds  up  its  protoplasm  out  of  the  simple  materials,  found 
in  rain-water,  which  make  up  its  food.    Metabolism  is  destruct- 


THE  ANIMAL  BODT. 


S7 


urticating 
use  of  the 
ste  is  dis- 

all  cells, 
digestive, 

it  differ 
er  knowl> 
nd  similar 


d  animals, 
tc.),  it  will 
»e  humble 
the  study 
ies  to  treat 
iest  living 
of  tissues, 
'6  made  of 
ever  large 

cally  must 
^n,  to  learn 
[)wn  inher- 
ing cells. 
>m  that  of 
I  direction 
some  f  unc- 
[>  meaning 
operties  in 
preceding 
l^iage  now 
operties  of 
ether  con- 
rming  the 
.  processes 
1  its  meta- 
iplex  com- 
otococcus- 
als,  found 
s  destruct- 


ive when  the  reverse  process  takes  place.  The  results  of  this 
process  are  eliminated  as  escareta,  or  useless  and  harmful  prod- 
ucts.  Since  all  the  vital  activities  of  cells  can  only  be  mani- 
fested when  supplied  with  food,  it  follows  that  living  organisms 
convert  potential  or  possible  energy  into  kinetic  or  actual  en- 
ergy. When  lifeless,  immobile  matter  is  taken  in  as  food  and, 
as  a  result,  is  converted  by  a  process  of  aasimUation  into  the 
protoplasm  of  the  cell  using  it,  we  have  an  example  of  poten- 
tial being  converted  into  actual  energy,  for  one  of  the  proper* 
ties  of  all  protoplasm  is  its  contractUUy.  Assimilation  implies, 
of  course,  the  absorption  of  what  is  to  be  used,  with  rejection 
of  waste  matters. 

The  movements  of  protoplasm  of  whatever  kind,  when  due 
to  a  stimulus,  are  said  to  indicate  irritabUity ;  while,  if  inde- 
pendent of  any  external  source  of  excitation,  they  are  denomi- 
nated automatic. 

Among  agents  that  modify  the  action  of  all  kinds  of  proto- 
plasm are  heat,  moisture,  electricity,  light,  and  others  in  great 
variety,  both  chemical  and  mechanical.  It  can  not  be  too  wJl 
remembered  that  living  things  are  what  they  are,  neither  by 
virtue  of  their  own  organization  alone  nor  through  the  action 
of  their  environment  alone  (else  would  they  be  in  no  sense  dif- 
ferent from  inanimate  things),  but  because  of  the  relation  of 
the  organization  to  the  surroundings. 

Protoplasm,  then,  is  contractile,  irritable,  automatic.,  absorp- 
tive, secretory  (and  excretory),  metabolic,  and  reprodudive. 

But  when  it  is  affirmed  that  these  are  the  fundamental  prop- 
erties of  all  protoplasm,  the  idea  is  not  to  be  conveyed  that  cells 
exhibiting  these  properties  are  identical  biologice^ly.  No  two 
masses  of  protoplasm  can  be  quite  alike,  else  would  there  be  no 
distinction  in  physiological  demeanor— no  individuality.  Every 
cell,  could  we  but  behold  its  inner  molecular  mechanism,  differs 
from  its  neighbor.  When  this  difference  reaches  a  certain  de- 
gree in  one  direction,  we  have  a  manifest  differentiation  leading 
to  physiological  division  of  labor,  which  may  now  with  advan- 
tage be  treated  in  the  following  section. 


THE  ANIMAL  BODY. 

An  animal,  as  we  have  learned,  may  be  made  up  of  a  single 
cell  in  which  each  part  performs  much  the  same  work ;  or,  if 
there  be  differences  in  function,  they  are  ill-defined  as  compared 


miilffviiiiiiftiiiiiiiMiiiiiia'iiaiiiiiii 


28 


ANIMAL  PHYSIOLOGY. 


with  those  of  higher  animals.  The  condition  of  things  in  such 
an  animal  as  Amoeba  may  be  compared  to  a  civilized  commu- 
nity in  a  very  crude  social  condition.  When  each  individual 
tries  to  perform  every  office  for  himself,  he  is  at  once  carpenter, 
blacksmith,  shoemaker,  and  much  more,  with  the  natural  re- 
sult that  he  is  not  efficient  in  any  one  direction.  A  commtmity 
may  be  judged  in  regard  to  its  degree  of  advancement  by  the 
amount  of  division  of  labor  existing  within  it.  Thus  is  it  with 
the  animal  body.  We  find  in  such  a  creature  as  the  fresh-water 
Hydra,  consisting  of  two  layers  of  cells  forming  a  simple  sac,  a 
slight  amount  of  advancement  on  Amoeba.  Its  external  surface 
no  longer  serves  for  inclosure  of  food,  but  it  has  the  simplest 
form  of  mouth  and  tentacles.  Each  of  the  cells  of  the  internal 
layer  seems  to  act  as  a  somewhat  improved  or  specialized  Amoe- 
ba, while  in  those  of  the  outer  layer  we  mark  a  beginning  of 
those  functions  which  i;aken  collectively  give  the  higher  ani- 
mals information  of  the  surrounding  world. 

niiooking  to  the  existing  state  of  things  in  the  universe,  it  is 
plam  that  an  animal  to  attain  to  high  ends  must  have  powers 
of  rapid  locomotion,  capacity  to  perceive  what  makes  for  its  in- 
terest, and  ability  to  utilize  means  to  attain  this  when  perceived. 
These  considerations  demand  that  an  animal  high  in  the  scale 
of  being  should  be  provided  with  limbs  sufficiently  rigid  to  sup- 
port its  weight,  moved  by  strong  muscles,  which  must  act  in 
harmony.  But  this  implies  abundance  of  nutriment  duly  pre- 
pared and  regularly  conveyed  to  the  bones  and  muscles.  All 
this  would  be  useless  unless  there  was  a  controlling  and  ener- 
gizing system  capable  both  of  being  impressed  and  originating 
impressions.  Such  is  found  in  the  nerves  and  nerve-centers. 
Again,  in  order  that  this  mechanism  be  kept  in  good  running 
order,  the  waste  of  its  own  metabolism,  which  chokes  and  poi- 
sons, must  be  got  rid  of — Whence  the  need  of  excretory  apparatus. 
In  order  that  the  nervous  system  may  get  sufficient  informa- 
tion of  the  world  around,  the  surface  of  the  body  must  be  pro> 
vided  with  special  message-receiving  offices  in  the  form  ot 
modified  nerve-endings.  In  short,  it  is  seen  that  an  animal  as 
high  in  the  scale  as  a  mammal  must  have  muscular,  osseous 
(and  connective),  digestive,  circulatory,  excretory,  and  nervous 
tissues ;  and  to  these  may  be  added  certain  forms  of  protective 
tissues,  as  hair,  nails,  etc. 

Assuming  that  the  student  has  at  least  some  general  knowl- 
edge of  the  structure  of  these  various  tissues,  we  propose  to  tell 
in  a  simple  way  the  whole  physiological  story  in  brief. 


THE  ANIMAL  BODY. 


» 


in  such 

commu- 

dividual 

arpenter, 

tural  re- 

oiiniuiity 

it  by  the 

is  it  with 

jsh-water 

)le  sac,  a 

d  surface 

simplest 

B  internal 

:ed  AmoB- 

inning  of 

gher  ani- 

rerse,  it  is 
ire  powers 
for  its  in- 
perceived. 
L  the  scale 
l^d  to  sup- 
ust  act  in 
duly  pre- 
scles.  All 
and  ener- 
riginating 
\re-centers. 
d  running 
>s  and  poi- 
apparatus. 
b  informa- 
st  be  pro- 
B  form  of 
animal  as 
ir,  osseous 
d  nervous 
protective 

ral  knowl- 
aose  to  tell 

9f. 


1  l*he  blood  is  the  source  of  all  the  nourishment  of  the  organ- 
ism, including  its  oxygen  supply,  and  is  carried  to  every  part  of 
the  body  through  elastic  tubes  which,  continually  branching 
and  becoming  gradually  smaller,  terminate  in  vessels  of  hair- 
like fineness  in  which  the  current  is  very  slow — a  condition  per- 
mitting that  interchange  between  the  cells  surrounding  them 
and  the  blood  which  may  be  compared  to  a  process  of  barter, 
the  cells  taking  nutriment  and  oxygen,  and  giving  (excreting) 
in  return  carbonic  anhydride.  BVom  these  minute  vessels  the 
blood  is  conveyed  back  toward  the  source  whence  it  came  by 
similar  elastic  tubes  which  gradually  increase  in  size  and  be- 
come fewer.  The  force  which  directly  propels  the  blood  in  its 
onward  course  is  a  muscular  pump,  with  both  a  forcing  and 
suction  action,  though  chiefly  the  former.  The  flow  of  blood 
is  maintained  constant  owing  to  the  resistance  in  the  smaller 
tubes  on  the  one  hand  and  the  elastic  recoil  of  the  larger  tubes 
on  the  other ;  while  in  the  returning  vessels  the  column  of 
blood  is  supported  by  elastic  double  gates  which  so  close  as  to 
prevent  reflux.  The  oxygen  of  the  blood  is  carried  in  disks  of 
microscopic  size  which  give  it  up  in  proportion  to  the  needs  of 
the  tissues  past  which  they  are  carried. 

(But  in  reality  the  tissues  of  the  body  are  not  nourished 
directly  by  the  blood,  but  by  a  fluid  derived  from  it  and  resem- 
bling it  greatly  in  most  particulars.  This  fluid  bathes  the 
tissue-cells  on  all  sides.  It  also  is  taken  up  by  tubes  that 
convey  it  into  the  blood  after  it  has  passed  through  little  fac- 
tories (lymphatic  glands),  in  which  it  undergoes  a  regeneration. 
Since  the  tissues  are  impoverishing  the  blood  by  withdrawal  of 
its  constituents,  and  adding  to  it  what  is  no  longer  useful,  and 
is  in  reality  poisonous,  it  becomes  necessary  that  new  material 
be  added  to  it  and  the  injurious  components  withdrawn.  The 
former  is  accomplished  by  the  absorption  of  the  products  of 
food  digestion,  and  the  addition  of  a  fresh  supply  of  oxygen 
derived  from  without,  while  the  poisonous  ingredients  that 
have  found  their  way  into  the  blood  are  got  rid  of  through 
processes  thut  may  be,  in  general,  compaped  to  those  of  a  sew- 
age system  of  a  very  elaborate  character.  To  explain  this  re- 
generation of  the  blood  in  somewhat  more  detail,  we  must  first 
consider  the  fate  of  food  from  the  time  it  enters  the  mouth  till 
it  leaves  the  tract  of  the  body  in  which  its  preparation  is 
carried  on. 

The  food  is  in  the  mouth  submitted  to  the  action  of  a  series 
of  catting  and  grinding  organs  worked  by  powerful  muscles ; 


f'l 


80 


ANIMAL  PHTSIOLOOY. 


mixed  with  a  fluid  which  changes  the  starchy  part  of  it  into 
sugar,  and  prepares  the  whole  to  pass  further  on  its  course : 
when  this  has  been  accomplished,  the  food  is  grasped  and 
squeezed  and  pushed  along  the  tube,  owing  to  the  action  of  its 
own  muscular  cells,  into  a  sac  (stomach),  in  which  it  is  rolled 
about  and  mixed  with  certain  fluids  of  peculiar  chemical  com- 
position derived  from  cells  on  its  inner  surface,  which  trans- 
form the  proteid  part  of  the  food  into  a  form  susceptible  of 
ready  use  (absorption).  When  this  saccular  organ  has  done 
its  share  of  the  work,  the  food  is  moved  on  by  the  action  of 
the  muscles  of  its  walls  into  a  very  long  portion  of  the  tract  in 
which,  in  addition  to  processes  carried  on  in  the  mouth  and 
stomach,  there  are  others  which  transform  the  food  into  a 
condition  in  which  it  can  pass  into  the  blood.  Thus,  all  of 
the  food  that  is  susceptible  of  changes  of  the  kind  described  is 
acted  upon  somewhere  in  the  long  tract  devoted  to  this  task. 
But  there  is  usually  a  remnant  of  indigestible  material  which 
is  finally  evacuated.  How  is  the  prepared  material  conveyed 
into  the  blood  ?  In  part,  directly  through  the  walls  of  the 
minutest  blood-vessels  distributed  throughout  the  length  of 
this  tube ;  and  in  part  through  special  vessels  with  appropriate 
cells  covering  them  which  act  as  minute  porters  (viUi). 

*(^he  impure  blood  is  carried  periodicrl?  *  ^o  %n  extensive  sur- 
face, usually  much  folded,  and  there  e;;*»  •(  in  the  hair-like 
tubes  referred  to  before,  and  thus  parts  «  e  excess  of  car- 
bon dioxide  and  takes  up  fresh  oxygen.  J..«  Ml  the  functions 
described  do  not  go  on  in  a  fixed  and  invariable  inanner,  but 
are  modified  somewhat  according  to  circimistances.  The  for- 
cing-pump of  the  circulatory  system  does  not  always  beat 
equally  fast;  the  smaller  blood-vessels  are  not  always  of  the 
same  size,  but  admit  more  or  less  blood  to  an  organ  according 
to  its  needs. 

\This  is  all  accomplished  in  obedience  to  the  commao'l..  car- 
ried from  the  brain  and  spinal  cord  along  the  nerves.  All 
movements  of  the  limbs  and  other  parts  are  executed  in  obe- 
dience to  its  behests ;  and  in  order  that  these  may  be  in  accord- 
ance with  the  best  interests  of  each  particular  orgam  and  the 
whole  animal,  the  nervous  centers,  which  may  be  compared  to 
the  chief  officers  of,  say,  a  telegraph  or  railway  system,  are  in 
constant  receipt  of  information  by  messages  carried  onward 
along  the  nerves.  The  command  issuing  is  always  related  to 
the  information  arriving. 

1  All  those  parts  commonly  known  as  sense-organs— the  eye« 


LIVINO  AND  LIFELESS  HATTER. 


81 


of  it  into 
8  course : 

iped  and 
ion  of  its 

is  rolled 
ical  Corn- 
ell trans- 
eptible  of 
has  done 
action  of 
le  tract  in 
louth  and 
od  into  a 
us,  all  of 
Mscribedis 
this  task, 
rial  which 
conveyed 
Us  of  the 
length  of 
ppropriate 

0. 

jnsive  sur- 
)  hair-like 
uss  of  car- 
functions 
anner,  but 
The  for- 
ways  beat 
»ys  of  the 
according 

nan 'I.,  car- 
rves.  All 
led  inobe- 

in  accord- 
Bcn  and  the 
tmpared  to 
tern,  are  in 
3d  onward 

related  to 

B— the  eye. 


ear,  nose,  tongue,  and  the  entire  surface  of  the  body — are  faith- 
ful reporters  of  facts.  They  put  the  inner  and  outer  worlds  iu 
communication,  and  without  them  all  higher  life  at  least  must 
cease,  for  the  organism,  like  a  train  directed  by  a  conductor  that 
disreganU  the  danger-signals,  must  work  its  own  destruction. 
Without  going  into  further  details,  suffice  it  to  say  that  the  pro- 
cesses of  the  various  cells  are  subordinated  to  the  general  good 
through  the  nervous  system,  and  that  susceptibility  of  proto- 
plasm to  stimuli  of  a  delicate  kind  which  enables  each  cell  to 
adapt  to  its  surroundings,  including  the  influence  of  remote  as 
well  as  neighboring  cells.  Without  this  there  could  be  no 
marked  advance  in  organisms,  no  differentiation  of  a  pro- 
nounced character,  and  so  none  of  that  physiological  division 
of  labor  which  will  be  inferred  from  our  brief  description  of 
the  functions  of  a  mammal.  The  whole  of  physiology  but 
illiistrates  this  division  of  labor. 

It  is  hoped  that  the  above  account  of  the  working  of  the 
animal  body,  brief  as  it  is,  may  serve  to  uhow  the  connection  of 
one  part  functionally  with  another,  for  it  is  much  more  impor- 
tant that  this  should  be  kept  in  mind  throughout,  than  that  all 
the  details  of  any  one  function  should  be  known. 


LIVINO  AND  UFELE8S  MATTER. 

In  order  to  enable  the  student  the  better  to  realize  the  na- 
ture of  living  matter  or  protoplasm,  and  to  render  clearer 
the  distinction  betw^t  n  the  forms  that  belong  to  the  organic 
and  inorganic  worlds  respectively,  we  shall  make  some  com- 
parisons in  detail  which  it  is  hoped  may  accomplish  this  ob- 
ject. 

(A  modem  watch  that  keeps  correct  time  must  be  regarded 
as  a  wonderful  object,  a  marvelous  triumph  of  human  skill. 
That  it  has  aroused  the  awe  of  savages,  and  been  mistaken  for 
a  living  being,  is  not  surprising.  But,  admirable  as  is  the 
result  attained  by  the  mechanism  of  a  watch,  it  is,  after  all, 
composed  of  but  a  few  metals,  etc.,  chiefly  in  fact  of  two,  brass 
and  steel;  these  ai-e,  however,  made  up  into  a  great  number 
of  different  parts,  so  adapted  to  one  another  as  to  work  in 
unison  and  accomplish  the  desired  object  of  indicating  the  time 
of  4ay. 

(Now,  however  well  constructed  the  watch  may  be,  there  are 
waste,  wear  and  tear,  which  will  manifest  themselves  more  and 


89 


ANIMAL  PHYSIOLOGY. 


more,  until  finally  the  machine  becomes  worthless  for  the  pur- 
pose of  its  construction.  If  this  mechanism  possessed  the 
power  of  adapting  from  without  foreign  matter  so  as  to  con- 
struct it  into  steel  and  brass  and  arrange  this  just  when  re- 
quired, it  would  imitate  a  living  organism;  but  this  it  can  not 
do,  nor  is  its  waste  chemically  different  from  its  component 
metals ;  it  does  not  break  up  brass  and  steel  into  something 
wholly  different.  In  one  particular  it  does  closely  resemble 
living  things,  in  that  it  griBidually  deteriorates ;  but  the  degra- 
dation of  a  living  cell  is  the  consequence  of  an  actual  change 
in  its  component  parts,  commonly  a  fatty  degeneration.  The 
one  is  a  real  transformation,  the  other  mere  wear. 

Had  the  watch  the  power  to  give  rise  to  a  new  one  like  itself 
by  any  process,  especially  a  process  of  division  of  itself  into  two 
parts,  we  should  have  a  parallel  with  living  forms;  but  the 
watch  can  not  even  renew  its  own  jiarts,  much  less  give  rise  to 
a  second  mechanism  like  itself.  Here,  then,  is  a  manifest  dis- 
tinction between  living  and  inanimate  things. 

Suppose  further  that  the  watch  was  so  constructed  that, 
after  the  lapse  of  a  certain  time,  it  underwent  a  change  in  its 
inner  machinery  and  perhaps  its  outer  form,  so  as  to  be  scarcely 
recognizable  as  the  same ;  and  that  as  a  result,  instead  of  indi- 
cating the  hours  and  minutes  of  a  time-reckoning  adapted  to 
the  inhabitants  of  our  globe,  it  indicated  time  in  a  wholly  dif- 
ferent way ;  that  after  a  series  of  such  transformations  it  fell  to 
pieces— took  the  original  form  of  the  metals  from  which  it 
was  constructed— we  should  then  have  in  this  succession  of 
events  a  parallel  with  the  development,  decline,  and  death  of 
living  organisms. 

(la  another  particular  our  illustration  of  a  watch  may  serve 
a  useful  purpose.  Suppose  a  watch  to  exist,  the  works  of  which 
are  so  concealed  as  to  be  quite  inaccessible  to  our  vision,  so  that 
all  we  know  of  it  is  that  it  has  a  mechanism  which  when  in 
action  we  can  hear,  and  the  result  of  which  we  perceive  in  the 
movements  of  the  hands  on  the  face;  we  should  then  be  in  the 
exact  position  in  reference  to  the  watch  that  we  now  are  as  re- 
gards the  molecular  movements  of  protoplasm.  On  the  latter 
the  entire  behavior  of  living  matter  depends;  yet  it  is  abso- 
lute hidden  from  us. 

^e  know,  too,  that  variations  must  be  produced  in  the 
mechanism  of  time-pieces  by  temperature,  moisture,  and  other 
influences  of  the  environment,  resulting  in  altered  action.  The 
same,  as  will  be  shown  in  later  chapters,  occurs  in  protoplasm. 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM. 


88 


or  the  pur- 
ssessed  the 

0  as  to  con- 
it  when  re- 
8  it  can  not 
component 
something 

y  resemble 
;  the  degra- 
)ual  change 
ation.    The 

le  like  itself 
elf  into  two 
us;  but  the 
give  rise  to 
lanifest  dis- 

ructed  that, 
hange  in  its 
)  be  scarcely 
t«ad  of  indi- 
1^  adapted  to 
wholly  dif- 
ons  it  fell  to 
m  which  it 
iccession  of 
ad  death  of 

1  may  serve 
rks  of  which 
sion,  so  that 
lich  when  in 
rceive  in  the 
ten  be  in  the 
iw  are  as  re- 
>n  the  latter 
it  it  is  abso- 

iiced  in  the 
:e,  and  other 
action.  The 
protoplasm. 


This,  too,  is  primarily  a  molecular  effect.  If  the  works  of 
watches  were  beyond  observation,  we  should  not  be  able  to  state 
exactly  how  the  variations  observed  in  different  kinds,  or  even 
different  individuals  of  the  same  kind  occurred,  though  these 
differences  might  be  of  the  most  marked  character,  such  as  any 
one  could  recognize.  Here  once  more  we  refer  the  differences 
to  the  mechanism.  So  is  it  with  living  beings:  the  ultimate 
molecular  mechanism  is  unknown  to  us. 

(Gould  we  but  render  these  molecular  movements  visible  to 
our  eyes,  we  should  have  a  revelation  of  far  greater  scientific 
importance  than  that  unfolded  by  the  recent  researches  into 
those  living  forms  of  extreme  minuteness  that  swarm  every- 
where as  dust  in  a  sunbeam,  and,  as  will  be  learned  later,  are 
often  the  source  of  deadly  disease.  Like  the  movements  of  the 
watch,  the  activities  of  protoplasm  are  ceaseless.  A  watch  that 
will  not  run  is,  as  such,  worthless — it  is  mere  metal — ^has  under- 
gone an  immense  degradation  in  the  scale  of  values;  so  proto- 
plasm is  no  longer  protoplasm  when  its  peculiar  molecular 
movements  cease ;  it  is  at  once  degraded  to  the  rank  of  dead 
matter. 

The  student  may  observe  that  each  of  the  four  propositions, 
embodying  the  fundamental  properties  of  living  matter,  stated 
in  the  preceding  chapter,  have  been  illustrated  by  the  simile  of 
a  watch.  Such  an  illustration  is  necessarily  crude,  but  it  helps 
one  to  realize  the  meaning  of  truths  which  gather  force  with 
each  living  form  studied  if  regarded  aright ;  and  it  is  upon  the 
(rvtdizaiiQiLPt  traji^  that  mental  growth  as  well  as  practical 
efficiency  depends. 


0LA88IFI0ATI0N  OF  THE  ANDCAL  KINODOM. 

( There  are  human  beings  so  low  in  the  scale  as  not  to  possess 
such  general  terms  as  tree,  while  they  do  employ  names  for  dif- 
ferent kinds  of  trees.  The  use  of  such  a  word  as  ''tree"  im- 
plies generalization,  or  the  abstraction  of  a  set  of  qualities  from 
the  things  in  which  they  reside,  and  making  them  the  basis  for 
the  grouping  of  a  multitude  of  objects  by  which  we  are  sur- 
rounded. Manifestly  without  such  a  process  knowledge  must 
be  very  limited,  and  the  world  without  significance ;  while  in 
proportion  as  generalization  may  be  safely  widened,  is  our 
progress  in  the  un^eation  of  knowledge  toward  which  science 
is  tending.  But  it  also  follows  that  without  complete  knowl- 
s 


84 


ANIMAL  PHTSIOLOOT. 


edge  there  can  be  no  perfect  classification  of  objects;  hence, 
any  classification  must  be  regarded  but  as  the  temporary  creed 
of  science,  to  be  modified  with  the  extension  of  knowledge.  As 
a  matter  of  fact,  this  has  been  the  history  of  all  zodlogical  and 
other  systems  of  arrangement.  The  only  purpoee  of  grouping 
is  to  simplify  and  extend  knowledge ;  this  being  the  case,  it  fol- 
lows that  a  method  of  grouping  that  accomplishes  this  has 
value,  though  the  system  may  be  artificial  that  is  based  on 
resemblances  which,  though  real  and  constant,  are  associated 
with  differences  so  numerous  and  radical  that  the  total  amount 
of  likeness  between  objects  thus  grouped  is  often  less  than  the 
difference.  Such  a  system  was  that  of  Linneeus,  who  classified 
plants  according  to  the  number  of  stamens,  etc.,  they  bore. 

Seeing  that  animals  which  resemble  each  other  are  of  com- 
mon descent  from  some  earlier  form,  to  establish  the  line  of  de- 
scent is  to  determine  in  great  part  the  classification.  Much  as- 
sistance in  this  direction  is  derived  from  embryology,  or  the 
history  of  the  development  of  the  individual  {ontogeny);  so 
that  it  may  be  said  that  the  ontogeny  indicates,  though  it  does 
not  actually  determine,  the  line  of  descent  {phytogeny) ;  and  it 
is  owing  to  the  importance  of  this  truth  that  naturalists  have 
in  recent  years  given  so  much  attention  to  comparative  embry- 
ology. 

It  will  be  inferred  that  a  nattrnd  system  of  classification  must 
be  based  both  on  function  and  structure,  though  chiefly  on  the 
latter,  since  organs  of  very  different  origin  may  have  a  similar 
function ;  or,  to  express  this  otherwise,  homologous  structures 
may  not  be  analogous;  and  homology  gives  the  better  basis  for 
classification.  To  illustrate,  the  wing  of  a  bat  and  a  bird  are 
both  homologous  and  analogous;  the  wing  of  a  butterfly  is 
analogous  but  not  homologous  with  these ;  manifestly,  to  clas- 
sify bats  and  birds  together  would  be  better  than  to  put  birds 
and  insects  in  the  same  group,  thus  leaving  other  points  of  re- 
lationship out  of  consideration. 

The  broadest  possible  division  of  the  animal  kingdom  is  into 
groups,  including  respectively  one-celled  and  many-celled 
forms — i.  e.,  into  Protozoa  and  Metatsoa.  As  the  wider  the 
grouping  the  less  are  differences  considered,  it  follows  that  the 
more  subdivided  the  groups  the  more  complete  is  the  informa- 
tion conveynl  •  thus,  to  say  that  a  dog  is  a  metazoan  is  to  con- 
vey a  certa.  amount  of  information ;  that  it  is  a  vertebrate, 
more ;  that  it  is  a  mammal,  a  good  deal  more,  because  each  of 
the  latter  terms  includes  the  former. 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM.- 


85 


ts;  hence, 
rary  creed 
edge.    As 
)gical  and 
grouping 
sase,  it  fol- 
ia this  has 
based  on 
associated 
tal  amount 
than  the 
o  classified 
r  bore, 
ire  of  com- 
)  line  of  de- 
Much  as- 
ogy,  or  the 
logeny);  so 
>ugh  it  does 
ny) ;  and  it 
ralists  have 
tive  embry- 

cation  must 
iiiefly  on  the 
bve  a  similar 
18  structures 
;ter  basis  for 
d  a  bird  are 
butterfly  is 
Nstly,  to  clas- 
to  put  birds 
points  of  re- 

gdom  is  info 
many-celled 
e  wider  the 
lows  that  the 
the  informa- 
Eui  is  to  con- 
a  vertebrate, 
ause  each  of 


Animal 
King- 
dom. 


Inverte- 
brata. 


Vertebrata. 


Protozoa  (amoeba,  vorticella,  etc.). 
Coelenterata  (sponges,  jelly-fish,  polyps,  etc.). 
Eckinodermata  (star-flsh,  sea-urchins,  etc.). 
Vermes  (worms). 

Arthropods  (crabs,  insects,  spiders,  etc.). 
Mollusca  (oysters,  snails,  etc.). 
MoUusooidea  (moss-like  animals). 
.  Tunicata  (ascidians). 

Pisces  (fishes). 

Amphibia  (frogs,  menobranchus,  etc.). 

Beptilia  (snakes,  turtles,  etc.). 

Aves  (biids). 

Mammalia  (domestic  quadrupeds,  etc.). 


The  above  classification  (of  Glaus)  is,  like  all  such  arrange- 
ments, but  the  expression  of  one  out  of  many  methods  of  view- 
ing the  animal  kingdom. 

I «  .  the  details  of  classification  and  for  the  grounds  of  that 
Wb  \ave  presented,  we  refer  the  student  to  works  on  zoology; 
but  we  advise  those  who  are  not  familiar  with  this  subject, 
when  a  technical  term  is  used,  to  think  of  that  animal  belong- 
ing to  the  group  in  question  with  the  structure  of  which  they 
are  best  acquainted. 

Man's  Place  in  the  Animal  Kingdom. 

QEt  is  no  longer  the  cuistom  with  zoologists  to  place  man  in 
an  entirely  separate  group  by  himself ;  but  he  is  classed  with 
the  primates,  among  which  are  also  gn^ouped  the  anthropoid 
apes  (gorilla,  chimpanzee,  orang,  and  the  gibbon),  the  monkeys 
of  the  Old  and  of  the  New  World,  and  the  lemurs.  So  great  is 
the  structural  resemblance  of  man  and  the  other  primates  that 
competent  authorities  declare  that  there  is  more  difference  be- 
tween the  structure  of  the  most  widely  separated  members  of 
the  group  than  between  certain  of  the  anthropoid  apes  and  man. 

The  points  of  greatest  resemblance  between  man  and  the 
anthropoid  apes  are  the  following :  The  same  number  of  verte- 
bree ;  the  same  general  shape  of  the  pelvis ;  a  brain  distinguish- 
ing them  from  other  mammals ;  and  posture,  being  bipeds. 

The  distinctive  characters  are  size,  rather  than  form  of  the 
brain,  that  of  man  being  more  than  twice  as  large ;  a  relatively 
larger  cranial  base,  by  which,  together  with  the  greater  size  of 
the  jaws,  the  face  becomes  prominent ;  the  earlier  closure  of 
the  sutures  of  the  cranium,  arresting  the  growth  of  the  brain ; 
more  developed  canine  teeth  and  difference  in  the  order  of 
eruption  of  the  permanent  teeth ;  the  more  posterior  position 
of  the  foramen  magnum ;  the  relative  length  of  the  limbs  to 


AT 


89 


ANIMAL  PHYSIOLOOT. 


each  other  and  the  rest  of  the  body ;  minor  differences  in  the 
hands  and  feet,  especially  the  greater  freedom  and  power  of 
apposition  of  the  great-toe. 

But  the  greatest  distinction  between  man  and  even  his 
closest  allies  among  the  apes  is  to  be  found  in  the  development 
to  an  incomparably  higher  degree  of  his  intellectual  and  moral 
nature,  corresponding  to  the  differences  in  weight  and  structure 
of  the  human  brain,  and  associated  with  the  use  of  spoken  and 
written  language ;  so  that  the  experience  of  previous  genera- 
tions is  not  only  registered  in  the  organism  (heredity),  but  in  a 
form  more  quickly  available  (books,  etc.). 

The  greatest  structural  difference  between  the  races  of  men 
are  referable  to  the  cranium;  but,  since  they  all  interbreed 
freely,  they  are  to  be  considered  varieties  of  one  species. 


THE  LAW  OF  PERIODICITY  OR  RHYTHM  IN  NATURE. 

The  term  rhythm  to  most  minds  suggests  music,  poetry,  or 
dancing,  in  all  of  which  it  forms  an  essential  part  so  simple, 
pronounced,  and  uncomplicated  as  to  be  recognized  by  all  with 


The  regular  division  of  music  into  bars,  the  recurrence  of 
chords  of  the  same  notes  at  certain  intervals,  of  forte  and  piano, 
seem  to  be  demanded  by  the  very  nature  of  the  human  mind. 
The  same  applies  to  poetry.  Even  a  child  that  can  not  under- 
stand the  language  used,  or  an  adult  listening  to  recitations  in 
an  unknown  tongue,  enjoys  the  flow  and  recurrences  of  the 
sounda  Dancing  has  in  all  ages  met  a  want  in  human  organi- 
zations, which  is  partly  supplied  in  quieter  inoods  by  the  regu- 
larity of  the  steps  in  walking  and  similar  simple  movements. 

r^ut  as  rhythm  runs  through  all  the  movements  of  animals, 
so  is  it  also  found  in  all  literature  and  all  art.  Infinite  variety 
wearies  the  mind,  hence  the  fatigue  felt  by  the  sight-seer.  Re- 
currence permits  of  repose,  and  gratifies  an  established  taste  or 
appetite.  The  mind  delights  in  what  it  has  once  enjoyed,  in 
repetition  within  limita  Repetition  with  variety  is  manifestly 
a  condition  of  the  growth  and  development  of  the  mind.  This 
seems  to  apply  equally  to  the  body,  for  every  single  function 
of  each  organism,  however  simple  or  complex  it  may  be,  exem- 
plifies this  law  of  periodicity.  The  heart's  action  is  rhythmical 
{beats) ;  the  blood  flows  in  intermitting  gushes  from  the  central 
pump;  the  to-and-fro  movements  of  respiration  are  so  regular 


THE  LAW  OF  PBRIODICITT  OB  RHTTHH  IN  NATURE.      87 


7es  in  tlie 
power  of 

even  his 
relopment 
and  moral 

structure 
x>ken  and 
08  genera- 
),  but  in  a 

;e8  of  men 
interbreed 
;ies. 


'TATUBB. 

!,  poetry,  or 

so  simple, 

by  all  with 

purrence  of 
;  and  piano, 
iman  mind. 
L  not  under- 
citations  in 
noes  of  the 
nan  organi- 
>y  the  regu- 
^vements. 
of  animals. 
Elite  variety 
it-aeer.  Re- 
hed  taste  or 
enjoyed,  in 
I  manifestly 
mind.  This 
lie  function 
iy  be,  exem- 
rhythmical 
1  the  central 
e  so  regular 


that  their  cessation  would  arouse  the  attention  of  the  least 
instructed;  food  is  demanded  at  regular  intervals;  the  juices 
of  the  digestive  tract  are  poured  out,  not  constantly  but  period- 
ically; the  movements  by  which  the  food  is  urged  along  its 
path  are  markedly  rhythmic;  the  chemical  processes  of  the 
body  wax  and  wane  like  the  fires  in  a  furnace,  giving  rise  to 
regular  augmentations  of  the  temperature  of  the  body  at  fixed 
hours  of  the  day,  with  corresponding  periods  of  greatest  bodily 
activity  and  the  reverse. 

(^his  principle  finds  perfect  illustration  in  the  nervous  sys- 
tem. The  respiratory  act  of  the  higher  animals  is  effected 
through  muscular  movements  dependent  on  regular  waves  of 
excitation  reaching  them  along  the  nerves  from  the  central  cells 
which  regularly  discharge  their  forces  along  these  channels. 
Were  not  the  movements  of  the  body  periodic  or  rhythmical, 
instead  of  that  harmony  which  now  prevails,  every  muscular 
act  would  be  a  convulsion,  though  even  in  the  movements  of 
the  latter  there  is  a  highly  compounded  rhythm,  as  a  noise  is 
made  up  of  a  variety  of  musical  notes.  The  senses  are  subject 
to  the  same  law.  The  eye  ceases  to  see  and  the  ear  to  hear  and 
the  hand  to  feel  if  continuously  stimulated ;  and  doubtless  in 
all  art  this  law  is  unconsciously  recognized.  That  ceases  to  be 
art  which  fails  to  provide  for  the  alternate  repose  and  excita- 
tion of  the  senses.  The  eye  will  not  tolerate  continuously  one 
color,  the  ear  a  single  sound.  Why  is  a  breeze  on  a  warm  day 
so  refreshing  ?    The  answer  is  obvious. 

(XfOoking  to  the  world  of  animate  nature  as  a  whole,  it  is 
n<mced  that  plants  have  their  period  of  sprouting,  flowering, 
seeding,  and  decline ;  animals  are  born,  pass  through  various 
stages  to  maturity,  diminish  in  vigor,  and  die.  These  events 
make  epochs  in  the  life-history  of  each  species ;  the  recurrence 
of  w  aich  is  so  constant  that  the  agricultural  and  other  arrange- 
ments  even  of  savages  are  planned  accordingly.  That  the  in- 
dividuals of  each  animal  group  have  a  definite  period  of  dura- 
tion is  another  manifestation  of  the  same  law. 

(^Superficial  observation  suffices  to  furnish  facts  which  show 
that  the  same  law  of  periodicity  is  being  constantly  exemplified 
in  the  world  of  inanimate  things.  The  regular  ebb  and  flow  of 
the  tides ;  the  rise  and  subsidence  of  rivers ;  the  storm  and  the 
calm ;  summer  and  winter ;  day  and  night — are  all  recurrent, 
none  constant. 

[Events  apparently  without  any  regularity,  utterly  beyond 
any  law  of  recurrence,  when  sufficiently  studied  are  found  to 


■    i 


nnm 


mum 


8S 


ANIMAL  PHTSIOLOOT. 


fall  under  the  same  principle.  Thus  it  took  some  time  to  learn 
that  volcanic  eruptions  occurred  with  a  very  fair  degree  of 
regularity. 

in  judging  of  this  and  all  other  rhythmical  events  it  must 
he  borne  in  mind  that  the  time  standard  is  for  an  irregularity 
that  seems  large,  as  in  the  instance  just  referred  to,  becomes 
small  when  considered  in  relation  to  the  millions  of  years  of 
geological  time ;  while  in  the  case  of  music  a  trifling  irregu- 
larity, judged  by  fractions  of  a  second,  can  not  be  tolerated 
by  the  musical  organization — which  is  equivalent  to  saying 
that  the  interval  of  departure  from  exact  regularity  seems 
large. 

As  most  of  the  rhythms  of  the  universe  are  comimunded  of 
several,  it  follows  that  they  may  seem,  until  closely  studied, 
very  far  from  regular  recurrences.  This  may  be  observed  in 
the  interference  in  the  regularity  of  the  tides  themselves,  the 
daily  changes  of  which  are  subject  to  an  increase  and  decrease 
twice  in  each  month,  owing  to  the  influence  of  the  sun  and  moon 
being  then  either  coincident  or  antagonistic. 

In  the  functions  of  plants  and  animals,  rhythms  must  be- 
come very  greatly  compounded,  doubtless  often  beyond  recog- 
nition. 

i!Among  the  best  examples  of  rhythm  in  animals  are  daily 
sleep  and  winter  sleep,  or  hibernation ;  yet,  amid  sleep,  dreams 
or  recurrences  of  cerebral  activity  are  common — ^that  is,  one 
rhythm  (of  activity)  overlies  another  (of  repose).  In  like  man- 
ner many  hibernating  animals  do  not  remain  constantly  in  their 
dormant  condition  throughout  the  winter  months,  but  have 
periods  of  wakefulness ;  the  active  life  recurs  amid  the  life  of 
functional  repose. 

To  return  to  the  world  of  inanimate  matter,  W9  find  that  the 
crust  of  the  earth  itself  is  made  of  layers  or  strata  the  result  of 
periods  of  elevation  and  depression,  of  denudation  and  deposi- 
tion, in  recurring  order. 

The  same  law  is  illustrated  by  the  facts  of  the  economic  and 
other  conditions  of  the  social  state  of  civilized  men.  Periods 
of  depression  alternate  with  periods  of  revival  in  commercial 
life. 

There  are  periods  when  many  more  marriages  occur  and 
many  more  children  are  bom,  corresponding  with  ct^mges  in 
the  material  conditions  which  influence  men  as  well  as  other 
animals. 

Finally,  and  of  special  interest  to  the  medical  student,  are 


e  to  learn 
degree  of 

»  it  must 
regularity 
>,  becomes 
years  of 
ng  irregu- 
tolerated 
to  saying 
ity  seems 

oiinded  of 
ly  studied, 
bserved  in 
iselves,  the 
d  decrease 
I  and  moon 

s  must  be- 
ond  recog- 

i  are  daily 
sep,  dreams 
hat  is,  one 
a  like  man- 
itly  in  their 
,  but  have 
the  life  of 

nd  that  the 
he  result  of 
md  deposi- 

onomic  and 
n.  Periods 
commercial 

1  occur  and 
ct^anges  in 
)11  as  other 

student,  are 


THE  LAW  OP  PERIODICITY  OB  RHYTHM  IN  NATURE.      89 

the  laws  of  rhythm  in  disease.  Certain  fevers  have  their  regu- 
lar periods  of  attack,  as  intermittent  fever ;  while  all  diseases 
have  their  periods  of  exacerbation,  however  invariable  the 
sjrmptoms  may  seem  to  be  to  the  ordinary  observer  or  even  to 
the  patient  himself. 

Doubtless  the  fact  that  certain  hereditary  diseases  do  not 
appear  in  tLe  offspring  at  once,  but  only  at  the  age  at  which 
they  were  manifested  in  the  parents,  is  owing  to  the  same 
cause. 

Let  us  now  examine  more  thoroughly  into  the  real  nature  of 
this  rhythm  which  pervades  the  entire  universe. 

^  a  bow  be  drawn  across  a  violin-string  on  which  some  small 
pieces  of  paper  have  been  placed,  these  will  be  seen  to  fly  off ; 
and  if  the  largest  string  be  experimented  upon,  it  can  be  ob- 
served to  be  in  rapid  to-and-f  ro  motion,  known  as  vibration, 
which  motion  is  perfectly  regular,  a  definite  number  of  move- 
ments occurring  within  a  measured  period  of  time;  in  other 
words  the  motion  is  rhythmical  In  strings  of  the  finest  size 
the  motion  is  not  visible,  but  we  judge  of  its  existence  because 
of  the  result,  which  is  in  each  instance  a  sound.  Sound  is  to  us, 
however,  an  affection  of  the  nerve,  of  hearing  and  the  brain, 
owing  to  the  ribrations  of  the  ear  caused  by  similar  vibra- 
tions of  the  violin-strings.  The  movements  of  the  nerves  and 
nerve-cells  are  invisible  and  molecular,  and  we  seem  to  be 
justified  in  regarding  molectdar  movements  as  constant  and 
associated  with  aU  the  properties  of  matter  whether  living  or 
dead. 

^We  see,  then,  that  all  things  living  and  lifeless  are  in  con- 
staml  motion,  visible  or  invisible ;  there  is  no  such  thing  in  the 
universe  as  stable  equilibrium.  Change,  ceaseless  change,  is 
written  on  all  things;  and,  so  far  as  we  can  judge,  these 
changes,  on  the  whole,  tend  to  higher  development.  Neither 
rhythm,  however,  nor  anything  else,  is  perfect.  Even  the  mo- 
tions of  planets  are  subject  to  perturbations  or  irregularities 
in  their  periodicity.  This  subject  is  plainly  boundless  in  its 
scope.  We  have  introduced  it  at  this  stage  to  prepare  for  its 
study  in  detail  in  dealing  with  each  function  of  the  animal 
body.  If  we  are  correct  as  to  the  universality  of  the  law  of 
rhythm,  its  importance  in  biology  deserves  fuller  recognition 
than  it  has  yet  received  in  works  on  physiology;  it  will, ac- 
cordingly, be  frequently  referred  to  in  the  future  chapters  of 
this  book. 


" 


•-I 


BurnM 


40 


ANIMAL  PHTSIOLOGT. 


THE  LAW  OF  HABIT. 

Every  one  mast  have  observed  in  himself  and  others  the 
tendency  to  fall  into  set  ways  of  doing  certain  things,  in  which 
will  and  clear  purpose  do  not  come  prominently  into  view. 
Further  observation  shows  that  the  lower  animals  exhibit  this 
tendency,  so  that,  for  example,  the  habits  of  the  horse  or  the  dog 
may  be  an  amusing  reflection  of  those  of  the  master.  Trees  are 
seen  to  bend  permanently  in  the  direction  toward  which  the 
prevailing  winds  blow. 

The  violin  that  has  experienced  the  vibrations  aroused  by 
some  master's  hand  acquires  a  potential  musical  capability  not 
possessed  by  an  instrument  equally  good  originally,  but  the 
molecular  movements  of  which  never  received  such  an  educa- 
tion. 

It  appears,  then,  that  underlying  what  we  call  habit,  there  is 
some  broad  law  not  confined  to  living  things ;  indeed,  the  law  of 
habit  appears  to  be  closely  related  to  the  law  of  rhythm  we 
have  already  noticed.  Certain  it  is  that  it  is  inseparable  from 
all  biological  phenomena,  though  most  manifest  in  those  organ- 
isms provided  with  a  nervous  system,  and  in  that  system  itself. 
What  we  usually  call  habit,  however  expressed,  has  its  physical 
correlation  in  the  nervous  system.  We  may  refer  to  it  in  this 
connection  later :  but  the  subject  has  relations  so  numerous  and 
fundamental  that  it  seems  eminently  proper  to  introduce  it  at 
this  early  stage,  forming  as  it  does  one  of  those  comer-stones  of 
the  biological  building  on  which  the  superstructure  must  rest. 

When  we  seek  to  come  to  a  final  explanation  of  habit  in  this 
case,  as  in  most  others,  in  which  the  fundamental  is  involved, 
we  are  soon  brought  against  a  wall  over  which  we  are  unable 
to  climb,  and  through  which  no  light  comes  to  our  intellects. 

We  must  simply  believe,  as  the  result  of  observation,  that  it 
is  a  law  of  matter,  in  all  the  forms  manifested  to  us,  to  assume 
accustomed  modes  of  behavior,  perhaps  we  may  say  molecular 
movement,  in  obedience  to  inherent  tendencies.  But,  to  recog- 
nize this,  throws  a  flood  of  light  on  what  would  be  inexplicable, 
even  in  a  minor  degree.  We  can  not  explain  gravitation  in  it- 
self;  but,  assuming  its  universality,  replaces  chaos  by  order  in 
our  speculations  on  matter. 

Turning  to  living  matter,  we  look  for  the  origin  of  habit  in 
the  apparently  universal  principle  that  primary  molecular 
movement  in  one  direction  renders  that  movement  easier  after- 


THB  ORIGIN  OP  THR  P0RM8  OF  LIFR. 


41 


others  the 
I,  in  which 
into  view, 
ixhibit  this 
I  or  the  dog 
Trees  are 
which  the 

aroused  by 
ability  not 
ly,  but  the 
1  an  educa- 

bit,  there  is 
,  the  law  of 
rhythm  we 
urable  from 
ihose  organ- 
rstem  itself, 
its  physical 
to  it  in  this 
imerous  and 
;ioduce  it  at 
ler-stones  of 
e  must  rest, 
iiabit  in  this 
is  involved, 
are  unable 
intellects, 
ition,  that  it 
s,  to  assume 
y  molecular 
ut,  to  recog- 
nezplicable, 
itation  in  it- 
by  order  in 

1  of  habit  in 
T  molecular 
easier  after- 


ward, and  in  proportion  to  the  frequency  uf  repetition ;  which 
is  equivalent  to  saying  that  functional  activity  facilitates  func- 
tional activity.  Once  accepting  this  as  of  universal  application 
in  biology,  we  have  an  explanation  of  the  origin,  the  compara- 
tive rigidity,  and  the  necessity  of  habit.  There  must  be  a  phys- 
ical basis  or  correlative  of  all  mental  and  moral  habits,  as  well 
as  those  that  may  be  manifested  during  sleep,  and  so  purely  in- 
dependent of  the  will  and  consciousness.  We  are  brought,  in 
fact,  to  the  habits  of  cells  in  considering  those  organs,  and  that 
combination  of  structures  which  makes  up  the  complex  individ- 
ual mammal.  It  is  further  apparent  that  if  the  cell  can  trans- 
mit its  nature  as  altered  by  its  experiences  at  all,  then  habits 
must  be  hereditary,  which  is  known  to  be  the  case. 

Instincts  seem  to  be  but  crystallized  habits,  the  inherited 
results  of  ages  of  functional  activity  in  certain  well-defined 
directions. 

To  a  being  with  a  hi,9:hly  developed  moral  nature  like  man, 
the  lam  of  habit  is  one  of  great,  even  fearful  significance.  We 
make  t  i-day  our  to-mori  ow,  and  in  the  present  we  are  deciding 
the  future  of  others^  as  our  present  has  been  made  for  us  in  part 
by  our  ancest^TS.  We  shall  not  pursue  the  subject,  which  is  of 
boundlef!!;  extent  Jrurther  now,  but  these  somewhat  general 
statements  will  t^  amplifif^^d  and  fi.pplied  in  future  chapters. 


THF 


iGIN  OF  Tm    /ORMS  OF  LIFE. 


/It  is  a  matter  of  common  observation  that  animals  originate 
from  like  kinds,  and  plants  from  forms  ruo  .r:bling  themselves ; 
while  most  carefully  conducted  experiments  have  failed  to  show 
that  living  matter  can  under  any  circumstances  known  to  us 
arise  from  other  than  living  matter. 

That  in  a  former  condition  of  the  universe  such  may  have 
been  the  case  has  not  been  disproved,  and  seems  to  be  the  logical 
outcome  of  the  doctrine  of  evolution  as  applied  to  the  imiverse 
generally. 

^By  evolution  is  meant  the  derivation  of  more  complex  and 
di^erentiated  forms  of  matter  from  simpler  and  more  homogMie- 
^vc«  r  aes.  When  this  theory  is  applied  to  organized  or  liriiig 
forms,  it  is  termed  organic  evolution.  There  are  two  views  of 
the  origin  of  life:  the  one,  that  each  distinct  group  of  plants 
and  animals  was  independently  created ;  while  by  "  creation  "  is 
simply  meant  that  they  came  into  being  in  a  manner  we  know 


-  wM<".MW^WJ-i;..'^u.' — 


42 


ANIMAL  PHTSIOLOGT. 


not  how,  in  obedience  to  the  will  of  a  First  Catise.  The  other 
view  is  denominated  the  theory  of  descent  with  modification, 
the  theory  of  transmutation,  organic  evolution  etc.,  which 
teaches  that  all  the  various  forms  of  life  have  been  derived 
from  one  or  a  few  primordial  forms  in  harmony  with  the  recog- 
nized principles  of  heredity  and  variability.  The  most  widely 
known  and  most  favorably  received  exposition  of  this  theory  is 
that  of  Charles  Darwin,  so  that  his  views  will  be  first  presented 
in  the  form  of  a  hypothetical  case.  Assume  that  one  of  a  group 
of  living  forms  varies  from  its  fellows  in  some  particular,  and 
mating  with  another  that  has  similarly  varied,  leaves  progeny 
inheritinj^  this  characteristic  of  the  parents,  that  tends  to  be 
still  further  increased  and  rendered  permanent  by  successive 
pairing  with  forms  possessing  this  variation  in  form,  color,  or 
whatever  it  may  be.  We  may  suppose  that  the  variations  may 
be  numerous,  but  are  always  small  at  the  beginning.  Since  all 
animals  and  plants  tend  to  multiply  faster  than  the  means  of 
support,  a  competition  for  the  means  of  subsistence  arises,  in 
which  struggle  the  fittest,  as  judged  by  the  circumstances, 
always  is  the  most  successful ;  and  if  one  must  perish  outright, 
it  is  the  less  fit.  If  any  variation  arises  that  is  unfavorable  in 
this  contest,  it  will  render  the  possessor  a  weaker  competitor: 
hence  it  follows  that  only  useful  variations  are  preserved.  The 
struggle  for  existence  is,  however,  not  alone  for  food,  but  for 
anything  which  may  be  an  advantage  to  its  possessor.  One 
form  of  the  contest  is  that  which  results  from  the  rivalry  of 
members  of  the  same  sex  for  the  possession  of  the  females ;  and 
as  the  female  chooses  the  strongest,  most  beautiful,  most  active, 
or  the  supreme  in  some  respect,  it  follows  that  the  best  leave 
the  greatest  number  of  progeny.  This  has  been  termed  seeBtud 
selection. 

In  determining  what  forms  shall  survive,  the  presence  of 
other  plants  or  animals  is  quite  as  importuit  as  the  abun- 
dance of  food  and  the  physical  conditions,  often  more  so.  To 
illustrate  this  by  an  example :  Certain  kinds  of  clover  are  fer- 
tilized by  the  visits  of  the  bumble-bee  alone ;  the  numbers  of 
bees  existing  at  any  one  place  depends  on  the  abundance  of  the 
field-mice  which  destroy  the  nests  of  these  insects ;  the  numbers 
of  mice  will  depend  on  the  abundance  of  creatures  that  prey  on 
the  mice,  as  hawks  and  owls ;  these,  again,  on  the  creatures  that 
specially  destroy  them,  as  fuxes,  etc. ;  and  so  on,  the  chain  of 
connections  becoming  more  and  more  lengthy. 

If  a  certain  proportion  of  forms  varying  similarly  were  sep- 


THE  ORIGIN  OF  THE  FOBMS  OF  LIFK 


48 


The  other 

dification, 

c,  which 

n  derived 

the  recog- 

Mt  widely 

theory  is 

presented 

3f  a  group 

cular,  and 

progeny 

)ndB  to  be 

successive 

1,  color,  or 

itions  may 

Since  all 

means  of 

)  arises,  in 

imstances, 

1  outright, 

vorable  in 

ompetitor: 

rved.    The 

od,but  for 

ssor.     One 

I  rivalry  of 

nalee;  and 

lost  active, 

best  leave 

ned  sexual 

resence  of 
the  abun- 
)re  so.  To 
er  are  fer- 
umbers  of 
ince  of  the 
le  numbers 
At  pre;*  on 
fttures  that 
e  chain  of 

'  were  sep- 


arated by  any  great  natural  barrier,  as  a  chaia  of  lofty  mount- 
ains or  an  intervening  body  of  water  of  considerable  extent, 
and  so  prevented  from  breeding  with  forms  that  did  not  vary, 
it  is  clear  that  there  would  be  greater  likelihood  of  their  differ- 
ences being  preserved  and  augpnented  up  to  the  point  of  their 
greatest  usefulness. 

We  may  now  inquire  whether  such  has  actually  been  the 
course  of  events  in  nature.  The  evidence  may  be  arranged 
under  the  following  heads : 

1.  Mar^koiagf. — Briefly,  there  is  much  that  is  common  to 
entire  large  groups  of  animals ;  so  great,  indeed,  are  the  resem- 
blances throughout  the  whole  animal  kingdom,  that  herein  is 
fotMid  the  strongest  argument  of  all  for  the  doctrine  of  descent. 
To  illustrate  by  a  single  instance— fishes,  reptiles,  birds,  and 
mammals  possess  in  common  a  vertebral  colunm  bearing  the 
same  relationship  to  other  parts  of  the  animal  It  is  because  of 
resemblances  of  this  kind,  as  well  as  by  their  differences,  that 
naturalists  are  enabled  to  classify  animals. 

2.  Imlnryvlofy. — In  the  stages  through  which  animals  pass 
in  their  development  from  the  ovum  to  the  adult,  it  is  to  be  ob- 
served that  the  closer  the  resemblance  of  the  mature  organism 
in  different  groups,  the  more  the  embryos  resemble  one  another. 
Up  to  a  certain  stage  of  development  the  similarity  between 
groups  of  animals,  widely  separated  in  their  post-embryonic 
life,  is  marked:  thus  the  embryo  of  a  reptile,  a  bird,  and  a  mam- 
mal have  much  in  common  in  their  earlier  stages.  The  embryo 
of  the  mammal  passes  through  stages  which  represent  condi- 
tions which  are  permanent  in  lower  groups  of  animals,  as  for 
example  that  of  the  branchial  arches,  which  are  represented  by 
the  gills  in  fishes.  It  may  be  said  that  the  developmental  his- 
tory of  the  individual  (ontogeny)  is  a  brief  recapitulation  of 
the  development  of  the  specieis  (phylogeny).  Apart  from  the 
theory  of  descent,  it  does  not  seem  possible  to  gather  the  true 
significance  of  such  facts,  which  will  become  plainer  after  the 
study  of  the  chapters  on  reproduction. 

3.  Miaiary  may  be  cited  as  an  instance  of  useful  adapta- 
tion. Thus,  certain  beetles  resemble  bees  and  wasps,  which  lat- 
ter are  protected  by  stings.  It  is  believed  that  such  groups  of 
beetles  as  these  arose  by  a  species  of  selection ;  those  escaping 
enemies  which  chanced  to  resemble  dreaded  insects  most,  so 
that  birds  which  were  accustomed  to  prey  on  beetles,  yet  feared 
bees,  would  likewise  avoid  the  mimicking  forms. 

4.  Bndiairatary  Orgau.— Organs  which  were  once  functional 


44 


ANIMAL  PHTSIOLOOT. 


Fio.  47.— Show*  th*  embryoi  of  four  uwmn^li  In  Um  thrae 
oklf  (OX  nbUt  (B),  awl  a  niM  (M).   T1iir« 


opmrat,  which  the  thrw  eroHHrowi  (I, 
•■Mtly  u  powiblo.   Tho  lint,  or  oMNr 


omMHomi  of  th*  tlwM  WHnSi  itaiMorli^ 

n,  ni)  rtprwHt.  w«  wl(«t«d  to  oonrnvauA  ■• 

row,  I.  roprawat*  •  vmt  Murif  atajio,  with 

(middM)  oroi»row,  n,  wows  a  i 

more  dofidbntd 

of  the  •nbryonln  body  (the 


'  ataie,  with  the  flrat  rudlmaali  of  Umba,  whiia  the  Rlll-aMniivi  are  jrot  retalaed. 

-me  tbiriI(loweat)oroae-row,ItI,ihowaaetiU  teter atane,  wtth  uie  Umfae •    -i     -i 

aitd  the  itlll-opeBiiuM  loat   The 


gOi-opeiilnga,  and  wtthout  Hmfaa,  tKe  •eeond  (middle)  oroaa>row,  n,  Aiowa  a  aooewhat 
btor  ata«e,  with  the  flrat  rudlmaala  of  Umba,  w'  " 

riI(loweat)oroaa-row,ni,ahowaaatiU  late 

I  Itlll-opeBiiuM  kat  The  membnuaa  and  appendagee  ^     „ 

amnion,  jrptk-nae,  allantola)  are  omitted,  tlie  whole  Vwrive  (iRuraa  are  alvitly  mainlfled. 
the  upper  one*  more  than  the  lower.  To  fhoUltat*  the  oomparlaon.  ther  ar»  all  raduoiNl 
to  nearly  the  same  riae  in  the  oute.  All  the  embryoa  are  aaan  ftom  the  Mt  aide :  tlw  head 
•strmitr  la  above,  the  taaestrami^ below:  the arehad  bank  turned  to  the rlffat  The 
letter*  Indicate  the  aame  narta  In  all  the  twelve  flguraa,  nameljr :  v,  fore-brain ;  «,  twixt- 
brain ;  m,  mId-braIn  t  K  nhMMiraltt ;  n,  atlar-brain ;  r.  apinal  marrow :  «.  noae :  a,  ejw : 
o,  ear ;  k,  Rill-arebea ;  9,  heart ;  w,  vertabnl  oolumn;  /,  fore-Umba ;  6,  blnd-Umha ;  a,  tall. 
(After  Haeokel.) 


oarrttpoiid  m 


THE  OBIOIN  OF  THE  FORMS  OF  LIFE. 


4» 


in  a  more  ancient  form,  but  serve  no  use  in  the  creatures  in 
which  they  are  now  found,  have  reached,  it  is  thought,  their 
rudiments^  condition  through  long  periods  of  comparative 
disuse,  in  many  generations.  Such  are  the  rudimentary  mus- 
cles of  the  eais  of  man,  or  the  undeveloped  incisor  teeth  found 
in  the  upper  jaw  of  ruminants. 

6.  Oeographiflal  DiitribntioB. — It  can  not  be  said  that  animals 
and  plants  are  always  found  in  the  localities  where  they  are 
best  fitted  to  flourish.  This  has  been  well  illustrated  within 
the  lifetime  of  the  present  generation,  for  the  animals  intro- 
duced into  Australia  have  many  of  them  so  multiplied  as  to 
displace  the  forms  native  to  that  country.  But,  if  we  assume 
that  migrations  of  animals  and  transmutations  of  species  have 
taken  place,  this  difilculty  is  in  great  part  removed. 

6.  PalMBtology. — The  rooks  bear  record  to  the  former  exist- 
ence of  a  succession  of  related  forms ;  and,  though  all  the  in- 
termediate links  that  probably  existed  have  not  been  found, 
the  apparent  discrepancy  can  be  explained  by  the  nature  of 
the  circumstances  under  which  fossil  forms  are  preserved;  and 
the  "  imperfection  of  the  geological  record." 

It  is  only  in  the  sedimentary  rocks  arising  from  mad  that 
fossils  can  be  preserved,. and  those  animals  alone  with  hard 
parts  are  likely  to  leave  a  trace  behind  them ;  while  if  these 
sedimentary  rocks  with  their  inclosed  fossils  should,  owing  to 
enormous  pressure  or  heat  be  greatly  changed  (metamorphosed), 
all  trace  of  fossils  must  disappear — so  that  the  earliest  forms 
of  life,  those  that  would  most  naturally,  if  preserved  at  all,  be 
found  in  the  most  ancient  rocks,  are  wanting,  in  consequence 
of  the  metamorphism  which  such  formations  have  tmdergone. 
Moreover,  our  knowledge  of  the  animal  remains  in  the  earth's 
crust  is  as  yet  very  incomplete,  though,  the  more  it  is  explored, 
the  more  the  evidence  gathers  force  in  favor  of  organic  evolu- 
tion. But  it  must  be  remembered  that  those  groups  constitut- 
ing species  are  in  geological  time  intermediate  links. 

7.  1  «i|il  and  Iriatlag  BpmiM. — If  the  animals  and  plants  now 
peopling  the  earth  were  entirely  different  from  those  that  flour- 
ished in  the  past,  the  objections  to  the  doctrine  of  descent  would 
be  greatly  strengthened ;  but  when  it  is  found  that  there  is  in 
some  cases  a  scarcely  broken  succession  of  forms,  great  force  is 
added  to  the  arguments  by  which  we  are  led  to  infer  the  con- 
nection of  aU  forms  with  one  another. 

To  illustrate  by  a  single  instance :  the  existing  group  of 
horses,  with  a  single  toe  to  each  foot,  was  preceded  in  geological 


I 


a 


I 


4 


46 


ANIMAL  PHTSIOLOOT. 


time  in  America  by  forms  with  a  greater  number  of  toes,  the 
latter  increasing  according  to  the  antiquity  of   the  group. 


Flo.  48.— BoDM  of  the  feet  of  the  dUtorent  genera  of 
h^ipu$  (Eooene) :  b,  foot  ot  Att/Aitherium  (Lower 
oene) ;  <f ,  foot  of  the  reoent  geniie  iBgutw. 


(after  Kanh).    a,  foot  of  Oro- 
i> ;  e,  Coot  of  H^fparUm  CPikh 


These  forms  occur  in  succeeding  geological  formations.  It  is 
impossible  to  resist  the  conclusion  that  they  are  related  gene- 
alogically (phylogenetically). 

8.  PxoiprMiion.— Inasmuch  as  any  form  of  specialization  that 
would  give  an  animal  or  plant  an  advantage  in  the  struggle  for 
existence  would  be  preserved,  and  as  in  most  cases  when  the 
competing  forms  are  numerous  such  would  be  the  case,  it  is 
possible  to  understand  how  the  organisms  that  have  appeared 
have  tended,  on  the  whole,  toward  a  most  pronounced  pro- 
gression in  the  scale  of  existence.  This  is  well  illustrated 
in  the  history  of  civilization.  Barbarous  tribes  give  way  be- 
fore civilized  man  with  the  numberless  subdivisions  of  labor 
he  institutes  in  the  social  organism.  It  enables  greater  num- 
bers to  flourish  as  the  competition  is  not  so  keen  as  if  activities 
could  be  exercised  in  a  few  directions  only. 

9.  Donmtioated  Animak.— Darwin  studied  our  domestic  ani- 
mals long  and  carefully,  and  drew  many  important  conclusions 
from  his  researches.  He  was  convinced  that  they  }xad  all  been 
derived  from  a  few  wild  representatives,  in  accordance  with  the 
principles  of  natural  selection.  Breeders  have,  both  consciously 
and  unconsciously,  formed  races  of  animals  from  stocks  which 
the  new  groups  have  now  supplanted ;  while  primitive  man  had 
tamed  various  species  which  he  kept  for  food  and  to  assist  in 
the  chase,  or  as  beasts  of  burden.  It  is  impossible  to  believe 
that  all  the  different  races  of  dogs  have  originated  from  dis- 
tinct wild  stocks,  for  many  of  them  have  been  formed  within 
recent  periods ;  in  fact,  it  is  likely  that  to  the  jackal,  wolf,  and 


THE  ORIGIN  OP  THE  FORMS  OF  LIFE. 


47 


>f  toes,  the 
the  group. 


fox,  must  we  look  for  the  wild  progenitors  of  our  dogs.  Dar- 
win concluded  that,  as  man  had  only  utilized  the  materials  Na- 
ture provided  in  forming  his  races  of  domestic  animals,  he  had 
availed  himself  of  the  variations  that  arose  spontaneously,  and 
increased  and  fixed  them  by  breeding  those  possessing  the  same 
variation  together,  so  the  like  had  occurred  without  his  aid  in 
nature  among  wild  forms. 

Evolutionists  are  divided  as  to  the  origin  of  man  himself ; 
some,  like  Wallace,  who  are  in  accord  wi*\  Darwin  as  to  the 


.„o,  foot  of  Oro- 


ons.    It  is 
lated  gene- 

zation  that 
truggle  for 
s  when  the 
)  case,  it  is 
e  appeared 
nnced  pro- 
illustrated 
ve  way  be- 
is  of  labor 
eater  num- 
f  activities 

nestic  ani- 
onclusions 
emI  all  been 
!e  with  the 
onsciously 
tbks  which 
e  man  had 
so  assist  in 
to  believe 
from  dis- 
led  within 
I  wolf,  and 


«  J> 


no.  4>.— Skeleton  of  hand  or  ftm-foot  of  rix  mMnmeh,  I,  vama ;  U,  dog ;  m,  pig ;  IV,  ox ; 
V, tapir :  VI,  horee.  r,  radtM;  u, ulna;  a, eMpboid;  6, ■emi-luiwr;  e,  triquetnim (ounei- 
fonn) ;  d,  trapedum ;  e,  tr»peioid :  /,  cemtatum  (unciform  prooeiw) ;  g,  hamatum  (unci- 
form bone) ;  p.  pieifbrm ;  1,  thumb ;  I.  digit ;  8,  middle  finger ;  4.  rlng-ilnger ;  6,  little 
finger.   (After  (Mgenbaur.) 

origin  of  living  forms  in  general,  believe  that  the  theory  of 
natural  selection  does  not  suffice  to  account  for  the  intellectual 
and  moral  nature  of  man.  ^V'allace  believes  that  man's  body 
has  been  derived  from  lower  forms,  but  that  his  higher  nature 
is  the  result  of  some  unknown  law  of  accelerated  development ; 
while  Darwin,  and  those  of  his  way  of  thinking,  consider  that 
man  in  his  entire  nature  is  but  a  grand  development  of  powers 
existing  in  minor  degree  in  the  animals  below  him  in  *}-ii  scale. 
Bumauurj.-f Every  group  of  animals  and  plants  tends  to  in- 
crease in  nuntbers  in  a  geometrical  progression,  and  must,  if 
unchecked,  overrun  the  earth.  Every  variety  of  animals  and 
plants  imparts  to  its  offspring  a  general  resemblance  to  itself, 
but  with  minute  variations  from  the  original.  The  variations 
of  off  spring,  may  be  in  any  direction,  and  by  accumulation 


-mmmim 


48 


ANIMAL  PHYSIOLOGY. 


-"-^!SM^"---.--: 


THE  ORIGIN  OP  THE  FORMS  OP  LIFE. 


49 


'  * 


fiO 


ANFMAL  PHYSIOLOGY. 


Fio.  M.-HMU1  of  •  nose-ape  (Sent- 
nopitheeut  iwMioiu)  from  Bor- 
neo.   (After*Brdim.) 


rio.  87.— Head  of  JulU  Pw 
inuuL  (From  •  pnoto- 
grsph  bjr  Hintw.) 


constitute  fixed  differences  by  which  a  new  group  is  marked 
off.  In  the  determination  of  the  variations  that  persist,  the  law 
of  survival  of  the  fittest  operates. 


REPRObxjC?nON. 

As  has  been  already  noticed,  protoplasm,  in  whatever  form, 
after  passing  through  certain  stages  in  development,  undergoes 
a  decline,  and  finally  dies  and  joins  the  world  of  unorganized 
matter ;  so  that  the  permanence  of  living  things  demands  the 
constant  formation  of  new  individuals.     Groups  of  animals 
and  plants  from  time  to  time  become  extinct;  but  the  lifetime 
of  the  species  is  always  long  compared  with  that  of  the  individ- 
ual   Reproduction  by  division  seems  to  arise  from  an  exigency 
of  a  nutritive  kind,  best  exemplified  in  the  simpler  organisms. 
When  the  total  mass  becomes  too  great  to  be  supported  by 
absorption  of  pabulum  from  without  by  the  surface  of  the 
body,  division  of  the  organism  must  take  place,  or  death  ensues. 
It  appears  to  be  a  matter  of  indifference  how  this  is  accom- 
plished, whether  by  fission,  endogenous  division,  or  gemmation, 
so  long  as  separate  portions  of  protoplasm  result,  capable  of 
leading  an  independent  existence.    The  very  undifferentiated 
character  of  these  simple  forms  prepares  us  to  understand  how 
each  fragment  may  go  through  the  same  cycle  of  changes  as 
the  parent  form.    In  such  cases,  speaking  generally,  a  million 
individuals  tell  the  same  biological  story  as  one;  yet  these 
must  exist  as  individuals,  if  at  all,  and  not  in  one  great  united 
mass.    But  in  the  case  of  conjugation,  which  takes  place  some- 
times in  the  same  groups  as  also  multiply  by  division     >  its 
various  forms,  there  is  plainly  an  entirely  new  aspect  of  the 


ifBtfiw^wwii  tTtwrii:  w 


REPRODUCTION. 


51 


JuUkPa*- 
I  a,  photo- 


>  is  marked 
ist,  the  law 


ttever  form, 
b,  undergoes 
morganized 
emands  the 

of  animals 
the  lifetime 
the  wdivid- 
an  exigency 
'  organisms, 
ipported  by 
face  of  the 
eath  ensues. 
is  is  accom- 
gemmation, 
,  capable  of 
ifferentiated 
trstand  how 

changes  as 
y,  a  million 
;  yet  these 
ipreat  united 
place  some- 
'ision  '  ).  its 
ipect  of  the 


case  presented.  We  have  already  shown  that  no  two  cells,  how- 
ever much  alike  they  may  seem  as  regards  form  and  the  cir- 
cumstances under  which  they  exist,  can  have,  in  the  nature  of 
the  case,  precisely  the  same  history,  or  be  the  subjects  of  ex- 
actly the  same  experiences.  We  have  also  pointed  out  that  all 
these  phenomena  of  cell-life  are  known  to  us  only  as  adaptations 
of  internal  to  external  conditions ;  for,  though  we  may  not  be 
always  able  to  trace  this  connection,  the  inference  is  justi- 
fiable, because  there  are  no  facts  known  to  us  that  contradict 
such  an  assumption,  while  those  that  are  within  our  knowledge 
bear  out  the  generalization.  We  have  already  learned  that  liv- 
ing things  are  in  a  state  of  constant  chan|^,  as  indeed  are  all 
things ;  we  have  observed  a  constant  relation  between  certain 
changes  in  the  environment,  or  sum  total  of  the  surrounding 
conditions,  as,  for  example,  temperature  and  the  behavipr  of 
the  protoplasm  of  plants  and  animals ;  so  that  we  must  believe 
that  any  one  form  of  protoplasm,  however  like  another  it  may 
seem  to  our  comparatively  imperfect  observation,  is  different 
in  some  respects  from  every  other — as  different,  relatively,  as 
two  human  beings  living  in  the  same  community  during  the 
whole  of  their  lives ;  and  in  many  cases  as  unlike  as  individuals 
of  veiy  different  nationality  and  history.  We  are  aware  that 
when  two  such  persons  meet,  provided  the  unlikeness  is  not  so 
great  as  to  prevent  social  intercourse,  intercommunication  may 
prove  very  instructive.  Indeed,  the  latter  grows  out  of  the 
former ;  our  illustration  is  itself  explained  by  the  law  we  are 
endeavoring  to  make  plain.  It  would  appear,  then,  that  con- 
tinuous division  of  protoplasm  without  external  aid  is  not  pos- 
sible ;  but  that  the  vigor  necessary  for  this  must  in  some  way 
be  imparted  by  a  particle  (cell)  of  similar,  yet  not  wholly  like, 
protoplasm.  This  seems  to  furnish  an  explanation  of  the  neces- 
sity for  the  conjugation  of  Mving  forms,  and  the  differentiation 
of  sex.  Very  frequently  conjugation  in  the  lowest  animals  and 
plants  is  followed  by  long  periods  when  division  is  the  prevail- 
ing method  of  reproduction.  It  is  worthy  of  note,  too,  that 
when  living  forms  conjugate,  they  both  become  quiescent  for  a 
longer  or  shorter  time.  It  is  as  though  a  period  of  preparation 
preceded  one  of  extraordinary  activity.  ^We  can  at  present 
trace  only  a  few  of  the  steps  in  this  rejuvenation  of  life-stuff. 
Some  of  these  have  been  already  indicated,  which,  with  others, 
will  now  be  further  studied  in  this  division  of  our  subject,  both 
because  reproduction  throws  so  much  light  on  cell-life,  and  be- 
cause it  is  so  important  for  the  understanding  of  the  physio- 


i<>w<wwwwj!iMiwMJi<w.»i.iiiaiw.i 


iBmim  ininiiiiiiiuiiit>MiniJroiu  I 


f 


62 


ANIMAL  PHT8I0L00T. 


logical  behavior  of  tissues  and  organs.  It  may  be  said  to  be 
quite  as  important  tliat  the  ancestral  history  of  the  cells  of  an 
organism  be  known  as  the  history  of  the  units  composing  a 
community.  A,  B,  and  C  can  be  much  better  understood  if 
we  know  something  alike  of  the  history  of  their  race,  their  an- 
cestors, and  their  own  past ;  so  is  it  with  the  study  of  any  indi- 
vidual, animal,  or  group  of  animals  or  plants.  Accordingly, 
embryology,  or  the  history  of  the  origin  and  development  of 
tissues  and  organs,  will  occupy  a  prominent  place  in  the  va- 
rious chapters  of  this  work.  The  student  will,  therefore,  at 
the  outset  be  furnished  with  a  general  account  of  the  subject, 
while  many  details*  and  applications  of  principles  will  be  left 
for  the  chapters  that  treat  of  the  functions  of  the  various  organs 
of  animals.  The  more  knowledge  the  student  possesses  of  zo- 
ology the  better,  while  this  science  will  appear  in  a  new  light 
under  the  study  of  embryology. 

Animals  are  divisible,  according  to  general  structure,  into 
Protozoa,  or  unicellular  animals,  and  Metazoa,  or  multicellular 
forms — that  is,  animals  composed  of  cell  aggregates,  tissues,  or 
organs.  Among  the  latter  one  form  of  reproduction  appears 
for  the  first  time  in  the  animal  kingdom,  and  becomes  all  but 
universal,  though  it  is  not  the  exclusive  method ;  for,  as  seen  in 
Hydra,  both  this  form  of  generation  and  the  more  primitive 
gemmation  occur.  It  is  known  as  sexual  multiplication,  which 
usually,  though  not  invariably,  involves  conjugation  of  two  un- 
like cells  which  may  arise  in  the  same  or  different  individuals. 
That  these  cells,  known  as  the  male  and  female  elements,  the 
ovum  and  the  spermatozodn,  are  not  necessarily  radically  differ- 
ent, is  clear  f re  m  the  fact  that  they  may  arise  in  the  one  individ- 
ual from  the  iame  tissue  and  be  mingled  together.  These  cells, 
however,  li>e  all  others,  tell  a  story  of  continual  progressive 
differentiation  corp^sponding  to  the  advancing  evolution  of 
higher  from  lower  forms.  Thus  hermaphroditism,  or  the  coex- 
istence of  organs  for  the  production  of  male  and  of  female  cells 
in  the  same  individual,  is  confined  to  invertebrates,  among 
which  it  is  rather  the  exception  than  the  rule.  Moreover,  in 
such  hermaphrodite  forms  the  union  of  cells  with  greater  differ- 
ence in  experiences  is  provided  for  by  the  union  of  different  in- 
dividuals, so  that  commonly  the  male  cell  of  one  individual 
unites  with  (fertilizes)  the  female  cell  of  a  different  individual. 
It  sometimes  happens  that  among  the  invertebrates  the  cells 
produced  in  the  female  organs  of  generation  possess  the  power 
of  division,  and  continued  development  wholly  independently  of 


■>rwHii'WHt.U-<»fta<iP«0*i-irtl|gi'piwig 


itoluVtlBNOitl 


'I'"""  •?"'  -'•rnirnr[Tiiririii'"r"i"i'"'T  n  mmrotiiiiiyiw 


REPRODUCTION. 


68 


said  to  be 

cells  of  an 

imposing  a 

derstood  if 

e,  their  an- 

»f  any  indi- 

ccordingly, 

opment  of 

in  the  va- 

lerefore,  at 

he  subject, 

rill  be  left 

ious  organs 

esses  of  zo- 

a  new  light 

iictnre,  into 
ulticellular 
I,  tissues,  or 
ion  appears 
laen  all  but 
r,  as  seen  in 
e  primitive 
ition,  which 
a  of  two  un- 
individuala 
lements,  the 
ically  differ- 
one  individ- 
These  cells, 
progressive 
ivolution  of 
or  thecoex- 
female  cells 
fttes,  among 
loreover,  in 
eater  diff er- 
different  in* 
I  individual 
individual. 
;e8  the  cells 
9  the  power 
)endently  of 


the  access  of  any  male  cell  {parthenogeneaia) ;  such,  however,  is 
almost  never  the  exclusive  method  of  increase  for  any  group  of 
animals,  and  is  to  be  regarded  as  a  retention  of  a  more  ancient 
method,  or  perhaps  rather  a  reversion  to  a  past  biological  con- 
dition. No  instance  of  complete  parthenogenesis  is  known 
among  vertebrates,  although  in  birds  partial  development  of  the 
egg  may  take  place  independently  of  the  influence  of  the  male 
sex.  The  best  examples  of  parthenogenesis  are  to  be  found 
among  insects  and  crustaceans. 

It  is  to  be  remembered  that,  while  the  cells  which  fonn  the 
tissues  of  the  body  of  an  animal  have  become  specialized  to 
discharge  one  particular  function,  they  have  not  wholly  lost 
all  others ;  they  do  not  remain  characteristic  amoeboids,  as  we 
may  term  cells  closely  resembling  Amoeba  in  behavior,  nor  do 
they  wholly  forsake  their  ancestral  habits.  They  all  retain  the 
power  of  reproduction  by  division,  especially  when  young  and 
most  vigorous ;  for  tissues  grow  chiefly  by  the  production  of 
new  cells  rather  than  the  enlargement  of  fJready  mature  ones. 
Cells  wear  out  and  must  be  replaced,  which  is  effected  by  the 
processes  already  described  for  Amoeba  and  similar  forms. 
Moreover,  there  is  retained  in  the  blood  of  animals  an  army  of 
cells,  true  amoeboids,  ever  ready  to  hasten  to  repair  tissues  lost 
by  injury.  These  are  true  remnants  of  an  embryonic  condition ; 
for  at  one  period  all  the  cells  of  the  organism  were  of  this 
Tmdifferentiated,  plastic  character.  But  the  cell  (ovtim)  from 
which  the  individual  in  its  entirety  and  with  all  its  complexity 
arises  mostly  by  the  union  with  another  cell  {spermaiozodn), 
must  be  considered  as  one  that  has  remained  unspecialized 
and  retained,  and  perhaps  increased  its  reproductive  functions. 
They  certainly  have  become  more  complex.  The  germ-cell 
may  be  considered  unspecialized  as  regards  t>ther  functions,  but 
highly  specialized  in  the  one  direction  of  exceedingly  great 
capacity  for  growth  and  complex  division,  if  we  take  into  ac- 
count the  whole  chain  of  results ;  though  in  considering  this  it 
must  be  borne  in  mind  that  after  a  certain  stage  of  division 
each  individual  cell  repeats  its  ancestral  history  again ;  that  is 
to  say,  it  divides  and  gives  rise  to  cells  which  progress  in  turn 
as  well  as  multiply.  From  another  point  of  view  the  ovum  is 
a  marvelous  storehouse  of  energy,  latent  or  potential,  of  course, 
but  under  proper  conditions  liberated  in  varied  and  unexpected 
forms  of  force.  It  is  a  sort  of  storehouse  of  biological  energy 
in  the  most  concentrated  form,  the  liberation  of  which  in  sim- 
pler forms  gives  rise  to  that  complicated  chain  of  events  which 


\ 


i 


mmm 


iiu«imii 


64 


ANIMAL  PHTSIOLOOT. 


is  termed  by  tho  biologfist  development,  but  which  may  be  ex- 
pressed hy  1  '■:<  >  phyBiologist  as  the  transformation  of  potential 
into  k)u:i;  euorgy,  or  the  energfy  of  motion.  Viewed  chemic- 
ally, it  it  :'■,.■!  r i;  ■•■  ep.'ated  story  of  the  production  of  forms,  of 
greater  s\,>-::,Aity  and  simplicity,  from  more  unstable  and  com- 
plex ones,  involving  throughout  the  process  of  oxidation ;  for  it 
must  ever  be  kept  in  mind  that  life  and  oxidation  are  concomi- 
tant and  inseparable.  The  further  study  of  reproduction  in  the 
concrete  will  render  the  meaning  and  force  of  many  of  the 
above  statements  clearer. 


The  Ovum. 

The  typical  female  cell,  or  ovum,  consists  of  a  mass  of  proto- 
plasm, usually  globular  in  form,  containing  a  nucleus  and  nu- 
cleolus. 

The  ovum  may  or  may  not  be  invested  by  a  membrane ;  the 
protoplasm  of  the  body  of  the  cell  is  usually  highly  granular, 
and  may  have  stored  up  within  it  a  varying  amount  of  proteid 
material  (food-yelk),  which  has  led  to  division  of  ova  into 
classes,  according  to  the  manner  of  distribution  of  this  nutri- 
tive reserve.  It  is  either  concentrated  at  one  pole  {tdoleeUh- 
al) ;  toward  the  center  {centrolecithal) ;  or  evenly  distributed 

throughout  {alecUhal).  Dur- 
ing development  this  material 
is  converted  by  the  agency  of 
the  cells  of  the  young  organ- 
ism {embryo)  into  active  pro- 
toplasm; in  a  word,  they  feed 
upon  and  assimilate  or  build 
up  this  food-stuff  into  their 
own  substance,  as  Amceba  does 
with  any  proteid  material  it 
appropriates. 

The  nucleus  {germinal  resi- 
de) is  large  and  well-defined, 
and  contains  within  itself  a 
highly  refractive  nucleolus 
{germinal  spot).  These  closely 
resemble  in  general  the  rest  of 
the  cell,  but  stain  more  deeply  and  are  chemically  different  in 
that  they  contain  nudeine  {nticleoplcsm,  chromatin). 

It  will  be  observed  that  the  ovun)  differs  in  no  essential  par- 


hia;  gv,  germinal  vesiole;  gt,  Rermliutt 
■pot. 


:''^v.i^'<,!.,t^'^^,-.^~„Miiim-ciiiSiSt.axi^r,taiia.!>im:^^ 


lay  "be  ex- 
potential 
chemic- 
forms,  of 
and  com- 
on ;  for  it 
concomi- 
Ition  in  the 
Lny  of  the 


38  of  proto- 
ns and  nu- 

brane;  the 
Y  granular, 
i  of  proteid 
F  ova  into 
this  nutri- 
{telolecith- 
distributed 
iaZ).      Dur- 
lis  material 
B  agency  of 
ung  organ- 
active  pro- 
I,  they  feed 
te  or  build 
into  their 
.moeba  does 
material  it 

Tninal  vesi- 
'ell-defined, 
in   itself  a 

nucleolus 
lese  closely 

the  rest  of 
different  in 

sential  par- 


BEPRODUCTION. 


55 


Fio.  SO.— A  huniAii  egg  (much  enUrged)  from  the  oTarjr  of  a  female.  The  whole  egir  !■  • 
simple  mhericsl  cell.  The  creMer  part  of  this  cell  to  formed  by  the  egg-yttk,  by  the  gran- 
ular cell-aubatance  (pmtoplaam),  oonatoting  of  Innumerable  yelk-granule«  with  a  little 
inter-eranuUr  subetance.  In  the  upper  part  of  the  yelk  Ilea  the  briffht,  elobular,  germ- 
veeiole.  comapondiog  with  the  cell-kernel  (nueteiu).  Thto  containa  a  darker  geniMpot. 
anaweHng  to  the  nucleolus.  The  Klobular  yelk-nuMs  to  mnroundrd  by  a  thick,  light- 
colored  eKK-membrane  (tona  pettueuia,  or  chorion).  Thto  to  traversed  by  Tery  numeroua 
hair-like  lines,  radiating  toward  the  central  point  of  the  maas :  these  are  the  porous 
canals,  through  which,  in  the  course  of  fertHiiatlon,  the  thread-shaped,  active  sperm-ceUs 
penetrate  hito  the  egg-yelk.    (HaeckeL) 

ticular  of  structure  from  other  cells.  Its  differences  are  hidden 
ones  of  molecular  structure  and  functional  behavior.  In  ac- 
cordance with  the  diverse  circumstances  under  which  ova 
mature  and  develop,  certain  variations  in  structure,  mostly  of 
the  nature  of  additions,  present  themselves. 

Thus,  ova  may  be  naked,  or  provided  with  one  or  more 
coverings.  In  vertebrates  there  are  usually  two  membranes 
around  the  protoplasm  of  the  ovum :  a  delicate  covering  ( Vi- 
telline membrane),  beneath  which  there  is  another,  which 
is  sieve-like  from  numerous  perforations  {eona  radiata,  or  z. 
peUiicida).  The  egg  membrane  may  be  impregnated  with  lime 
salts  (sheU).  Between  the  membranes  and  the  yelk  there  is  a 
fluid  albuminous  substance  secreted  by  the  glands  of  the  ovi- 
duct, or  by  other  special  glands,  which  provide  proteid  nutri- 
ment in  different  physical  condition  from  that  of  the  yolk. 

The  general  naked-eye  appearances  of  the  ovum  may  be 
learned  from  the  examination  of  a  hen's  egg,  which  is  one  of 


^mm\  utawi  iMi ,  ntjtjj  lUM  n'.  »i 


56 


ANIMAL  PHYSIOLOGY. 


•1")! 

m 

III 
m 


the  most  complicated  known,  inasmuch  as  it  in  adapted  for 
development  outside  of  the  body  of  the  mother,  and  must,  con- 
sequently, be  capable  of  preserving  its  form  and  essential  vital 
properties  in  a  medium  in  which  it  is  liable  to  undergo  loss  of 
water,  protected  as  it  now  is  with  shell,  etc.,  but  which,  at  the 


eA.i 


Fta.  60.— DtagramniAttc  aection  of  an  unimpreKnated  fowl's  egg  (Foster  and  tialfonr,  after 
Allen  Thomson).  M,  blastoderm  or  cioatricula  ;  to.  y,  white  yolk ;  y.  y,  yellow  yelk ;  eh.  I, 
chalaia';  i.  m.  m,  inner  layer  of  shdl  membrane ;  «.  m.  outer  layer  of  diell  membrane ;  t, 
shell ;  a,  c.  k,  air-space  ;  to,  the  white  of  the  emr ;  v-  (i  vitelline  membrane ;  x,  the  denser 
albuminous  layer  tying  next  the  vitelUue  membrane, 

same  time,  permits  the  entrance  of  oxygen  and  moisture,  and 
conducts  heat,  all  being  essential  for  the  development  of  the 
germ  within  this  large  food-mass.  The  shell  serves,  evidently, 
chiefly  for  protection,  since  the  eggs  of  serpents  (snakes,  turtles, 
etc.)  are  provided  only  with  a  very  tough  membranous  cover- 
ing, this  answering  every  purpose  in  eggs  buried  in  sand  or 
otherwise  protected  as  theirs  usually  are.  As  the  hen's  egg  h 
that  most  readily  studied  and  most  familiar,  it  may  be  well  to 
describe  it  in  somewhat  further  detail,  as  illustrated  in  the 
above  figure,  from  the  examination  of  which  it  will  be  ap- 
parent that  the  yelk  itself  is  made  up  of  a  white  and  yellow 
portion  distributed  in  alternating  zones,  and  composed  of  cells 
of  different  microscopical  appearances.  The  clear  albumen  is 
stjructureless. 

The  relative  distribution,  and  the  nature  of  the  accessory  or 
non-essential  parts  of  the  hen's  egg,  will  be  understood  when  it 
is  remembered  that,  after  leaving  its  seat  of  origin,  which  will 
be  presently  described,  the  ovum  passes  along  a  tube  (oviduct) 


REPRODUCTION. 


67 


apted  for 
must,  con- 
intial  vital 
rgo  loss  of 
ich,  at  the 


id  Balfour,  after 
illow  yelk ;  eh.  I, 
U  membrane ;  «, 
« ;  X,  the  deoaer 


nature,  and 
lent  of  the 
,  evidently, 
Ices,  turtles, 
lous  cover- 
in  sand  or 
ten's  egg  iA 
be  well  to 
>ted  in  the 
(eill  be  ap> 
and  yellow 
sed  of  cells 
ilbumen  is 

ccessory  or 
•od  when  it 
which  will 
e  (oviduct) 


by  a  movement  imparted  to  it  by  the  muscular  walls  of  the 
latter,  similar  to  that  of  the  gullet  during  the  swallowing  gf 
food ;  that  this  tube  is  provided  with  glands  which  secrete  in 
turn  the  albumen,  the  membrane  (outer),  the  lime  salts  of  the 
shell,  etc.  The  twisted  appearance  of  the  rope-like  structures 
(chalazce)  at  each  end  is  owing  to  the  spiral  rotatory  movement 
the  egg  has  undergone  in  its  descent. 

The  air-chamber  at  the  larger  end  is  not  present  from  the 
first,  but  results  from  evaporation  of  the  fluids  of  the  albumen 
and  the  entrance  of  atmospheric  air  after  the  egg  is  laid  some 


time. 


The  ORiam  and  Development  of  the  Ovum. 


Between  that  protrusion  of  cells  which  gives  rise  to  the 
bud  which  develops  directly  into  the  new  individual,  and  that 
which  forms  the  ovary  with- 
in which  the  ovum  as  a  mod- 
ified cell  arises,  there  is  not 
in  Hyrlra  much  difference  at 
first  to  be  observed. 

In  the  mammal,  however, 
the  ovary  is  a  more  complex 
structure,  though,  relatively 
to  many  organs,  still  simple. 
It  consists,  in  the  main,  of 
connective  tissue  supplied 
with  vessels  and  nerves  in- 
closing modifications  of  that 
tissue  {Oraafian  foUides) 
within  which  the  ovum  is 
matured.  The  ovum  and  the 
follicles  arise  from  an  inver- 
sion of  epithelial  cells,  on  a 
portion  of  the  body  cavity 
{germinal  ridge),  which  give 
rise  to  the  ovum  itself,  and 
the  other  cells  surrounding 
it  in  the  Graafian  follicle. 
At  first  these  inversions  form 
tubules  {egg-tubes)  which  lat- 
er become  broken  up  into  iso- 
lated nests  of  cells,  the  fore-runners  of  the  Graafian  follicles. 

The  Graafian  follicle  consists  externally  of  a  fibrous  capsule 


Fts. 


61.— Section  through  portion  of  the  ovary 
<tf  mamma],  lUuntrMlng  mode  of  develop- 
ment of  the  Oraaflan  folUclea  (Wieder- 
■hetm>.  D,discuaproligen«;£i,  ripe  ovum; 
O,  foUioular  oelUi  of  {terminal  epithelium  ; 
g,  blooil-veaieiR ;  X'.  germinal  vuncle  (nuole- 
ui)and  germinal  spot  (nucleolus) :  KB,  ger- 
minal epitbeUum  ;  If,  liquor  folUculi ;  Mg, 
membrana  or  tuqlca  granulona,  or  follicular 
epttbeltum  ;  ifb,  lona  peltuoida  ;  M,  In- 
growtliM  from  toe  germinal  epltlielium,  ova- 
rian tubes,  by  P!e«aa  of  which  aome  of  the 
neata  retain  tb<$lr  oonneotkm  with  the  epithe- 
lium :  S,  cavity  which  appeara  within  the 
Oraaflan  follicle  ;  So,  itroma  of  ovary ;  I/, 
theoa  foUiPuli  or  capsule ;  V,  primitive  ova; 
When  an  ovum  with  ita  aurrounding  cell* 
ha*  become  neparated  from  the  nest,  it  is 
kn>  ;rn  as  a  Graaflan  follicle. 


rmmtni'Mi*  . 


58 


ANIMAL  PHTSIOLOOT. 


{tunica  fibrosa),  in  close  relation  to  which  is  a  layer  of  capillary 
hlood- vessels  {tunica  va^culosa),  the  two  together  forming  the 


Fio.  88.— Sagittal  sectir  a  of  the  ovary  of  on  adult  bltoh  (after  Wolder^r}.  o.  r,  ovarian  epi- 
thelium ;  n.  t,  ovarian  tubei ;  u.f.  younger  follicln ;  o./,  older  folUcle  ;  d.  p.  diocua  pro- 
ItHeruM,  with  the  ovum  ;  r,  epitneliura  of  a  leoond  ovum  in  the  tame  follicle  ;  /.  c,  flbroue 
coat  of  the  follicit; ;  p.  e,  proper  oooi.  of  the  follicle ;  «./•  epithelium  of  the  foQIcle  (mem- 
braiia  granuloRa) :  n./.  collapaed  atioi>hled  foUlole ;  b.  v,  blood-veMela ;  c.  (,  cell-tube*  of 
the  parovarium,  divided  longitudlnalhr  and  tronsvenwljr ;  t.  rf,  tubular  depreMrion  of  the 
ovanon  epithelium,  in  the  tmue  of  the  ovary ;  b.  e,  beginnlnff  of  the  ovarian  epithelium, 
close  to  the  lower  border  of  the  ovary. 

general  covering  {iunica  propria)  for  the  more  delicate  and  im- 
portant cells  within.  Lining  the  tunic  is  a  layer  of  small,  some- 
what cubical  cells  {membrana  granulosa),  which  at  one  part 
invest  the  ovum  several  layers  deep  {discus  proligerus),  while 
tho  remainder  of  the  space  is  filled  by  a  fluid  {liquor  foUiculi) 
prohablv  either  secretes!  by  the  cells  themselves,  or  resulting 
from  the  disintegration  of  some  of  them,  or  both. 


[»f  capillary 
>rming  the 


h.e. 


o.  e,  ovuion  epl- 
:  d.  p.  dtacus  pro- 
lltck) ;  /.  c,  flbroiM 
the  foUlcle  (mem- 
;  e.  (,  cell-tubes  of 
depraaBkm  of  the 
r«mii  epithelium, 


i&to  and  im- 
small,  Home- 
at  one  part 
tenia),  while 
tor  foUieuU) 
OT  resulting 


REPRODUCTION. 


59 


In  viewing  a  section  of  the  ovary  taken  from  a  mammal  at 
the  breeding-season,  ova  and  Graafian  follicles  may  be  seen  in 
all  stages  of  development — ^those,  as  a  rule,  nearest  the  surface 
being  the  least  matured.  The  Graafian  follicle  appears  to  pass 
inward,  to  undergo  growth  and  development  and  again  retire 
toward  the  exterior,  where  it  bursts,  freeing  the  ovum,  which  is 
conducted  to  the  site  of  its  future  development  by  appropriate 
mechanism  to  be  described  hereafter. 

Cltangei  in  the  Ovnm  itMl£ — The  series  of  transformations 
that  take  place,  in  the  ovum  before  and  immediately  after  the 
access  of  the  male  element  is,  in  the  opinion  of  many  biolo- 
gists, of  the  highest  significance,  as  indicating  the  course  evolu- 
tion has  followed  in  the  animal  kingdom,  as  well  as  instructive 
in  illustrating  the  behavior  of  nuclei  generally. 

The  germinal  vesicle  may  acquire  powers  of  slow  movement 
(amojboid),  and  the  germinal  spot  disappear :  the  former  passes 
to  one  surface  {pole)  of  the  ovum ;  both  these  structures  may 
undergo  that  peculiar  form  of  rearrangement  (karyokinesis) 
which  may  occur  in  the  nuclei  and  nucleoli  of  other  cells  prior 
to  division ;  in  other  words,  the  ovum  has  features  common  to 
it  and  many  other  cells  in  that  early  stage  which  precedes  the 
complicated  transformations  which  constitute  the  future  his- 
tory of  the  ovum. 

A  portion  of  the  changed  nucleus  {aster)  with  some  of  the 
protoplasm  of  the  cell  accumulates  at  one  surface  ( nole),  which 


Fio.  SB.— Formation  of  polar  cells  In  a  star-flsh  (A»teria»  glacialii)  (from  Gcddea,  A— K  after 
Fol,  L  after  O.  Hertwis).  A,  ripe  orum  with  eccentric  germinal  veaicle  and  Bpot ;  B— D, 
gradual  metamorphosM  of  Kermlnal  vesicle  and  spot,  as  seen  in  the  livinK  egg,  into  two 
asters ;  F,  formation  of  flrrt  polar  cells  aad  withdrawal  of  remaining  part  of  nuclear 
spindle  within  the  ovum  ;  O,  surface  view  of  llvinK  ovum  in  the  flrit  polar  cell ;  H,  com- 
pletion of  second  polar  cell ;  I.  a  later  stage,  sho\/uig  the  remaining  Internal  half  of  the 
spindle  In  the  form  of  two  clear  vesicles ;  K,  ovum  with  two  poUr  cells  and  radial  strln 
round  female  pronucleus,  as  seen  in  the  living  egg  (E,  F,  H,  and  I  from  picric  acid  prepa- 
rations) ;  L,  expulsion  of  the  first  polar  cell.    (Itaddou.) 

is  termed  the  upper  pole  because  it  is  at  this  region  that  the  epi- 
thelial cellfe  will  be  ultimately  developed,  and  is  separated ;  this 
process  is  repeated.    These  bodies  {polar  cells,  polar  globules. 


; ; 


60 


ANIMAL  PUTSIOLOOT. 


etc.),  then,  are  simply  expelled ;  they  take  no  part  in  the  devel- 
opment of  the  ovum ;  and  their  extrusion  is  to  be  regarded  as  a 
preparation  for  the  progress  of  the  cell,  whether  this  event  fol- 
lows or  precedes  the  entrance  of  the  male  cell  into  the  ovum. 
It  is  worthy  of  note  that  the  ovum  may  become  amoeboid  in  the 
region  from  which  the  polar  globules  are  expelled. 

The  remainder  of  the  nucleus  {female  proimcleus)  now 
passes  inward  to  undergo  further  changes  of  undoubted  im- 
portance, possibly  those  by  virtue  of  which  all  the  subsequent 
evolution  of  the  ovum  is  determined.  This  brings  us  to  the 
consideration  of  another  cell  destined  to  play  a  brief  but  im- 
portant r6le  on  the  biological  stage. 

The  Male  Cell  {Spermatozoon). 

This  cell,  almost  without  exception,  consists  of  a  nucleus 
(head)  and  vibratile  cilium.    However,  as  indicating  that  the 


Fm.  M.-Spermstmsoa  iiD  -Haddoa).  Not.  dr»wn  to  aciUe.  l.spongn  ;  S,h]rdrokl ;  8,  nema- 
tode ;  4,  oray-fl«li ;  ...  .  .tU  ;  6,  eleolric  ray  ;  7,  saUuniuider  ;  A,  hone  ;  U,  man.  Id  ninny 
■permatoioa,  as  in  No«.  7  and  9.  an  extremely  delicate  vibratile  band  ia  preaent. 


REPRODUCTION. 


61 


the  devel- 
:arded  as  a 

event  fol- 
the  ovum. 
x)id  in  the 

olens)  now 
oubted  im- 
subsequent 
us  to  the 
ef  but  im- 


'  a  nucleus 
ag  that  the 


latter  is  not  essential,  spermatozoa  without  such  an  appendage 
do  occur.  The  obvious  purpose  of  the  cilium  is  to  convey  the 
male  cell  to  the  ovum  through  a  fluid  medium — either  the  water 
in  which  the  ova  are  discharged  in  the  case  of  most  inverte- 
brates, or  through  the  fluids  that  overspread  the  surfaces  of  the 
female  generative  organs. 

The  Origin  of  the  SpemttOMSn.— The  structures  devoted  to 
the  production  of  male  cells  (testes),  when  reduced  to  their  es- 


hydroM ;  3.  nema- 
U,  man.  Id  mnny 
present. 


Fio.  3&.~4iwniiatoi(eiie*to.  A-H.  Isolated  sperm-orlls  of  the  rat,  showing  the  development 
of  thi)  npermatoaufln  and  Urn  gradual  tnuMformatloD  of  the  nucleus  into  the  ■pennatocoan 
riMd.  In  O  lbs  seminal  granule  is  being  oast  off  (after  H.  H.  Brown).  I— H,  speita-celli 
of  an  ElaHmobranoh.  The  nucleus  of  «Mh  cell  divides  Into  a  large  number  of  daughter- 
nuclei,  each  one  of  which  is  converted  ialo  the  rod-like  bead  of  a  spermatosoOn.  NTtrans- 
verse  ssotion  of  a  ripe  cell,  showii^  the  bundle  of  spermstoaoa  and  the  passive  nucleus 
a— N,  after  Semper).  O-S,  spermatogenesis  In  the  earth-worm  :  O,  young  sperm-cell ; 
I .  the  same  divided  Into  four ;  g,  spsrmatosphere  with  the  central  spertrlilastophore ; 
K, .)  later  Bt«ge :  8,  nearly  mature  apeniM^osoa.    (After  BlomHeld. ) 

sentials,  consist  of  tubules,  of  great  length  in  mammals,  lined 
with  nucleated  epithelial  cells,  from  which,  by  a  series  of 


62 


ANIMAL  PHYSIOLOGY. 


li 


m 


changes  figured  above,  a  general  idea  of  their  development  may 
be  obtained. 

It  will  be  observed  that  throughout  the  series  the  nucleus  of 
the  cell  is  in  every  case  preserved,  and  finally  becomes  the  head 
of  the  male  cell.  Once  more  we  are  led  to  see  the  importance 
of  this  structure  in  the  life  of  the  cell. 

Fertilisation  of  the  Oram. — ^The  spermatozoon,  lashing  its  way 
along,  when  it  meets  the  ovum,  enters  it  either  through  a  special 
minute  gateway  {micropyle),  or  if  this  be  not  present — as  it  is 
not  in  the  ova  of  all  animals — it  actually  penetrates  the  mem- 
branes and  substance  of  the  female  cell,  and  continues  active 
till  the  female  pronucleus  is  reached,  when  the  head  enters  and 
the  tail  is  absorbed  or  blends  with  the  female  cell.  The  nucleus 
of  the  male  cell  prior  to  union  with  the  nucleus  of  the  ovum 
undergoes  changes  similar  to  those  that  the  nucleus  of  the 
ovum  underwent,  and  thus  becomes  fitted  for  its  special  func- 
tions as  a  fertilizer;  or  perhaps  it  would  be  more  correct  to  say 
that  these  altered  masses  of  nuclear  substance  mutually  fertil- 
ize each  other,  or  initiate  changes  the  one  in  the  other  which 
conjointly  result  in  the  subsequent  stages  of  the  development 
of  the  ovum.  The  altered  male  nucleus  {male  pronucleus),  on 
reaching  the  female  pronucleus,  finds  it  somewhat  amseboid, 
a  condition  which  may  be  shared  in  some  degree  by  the  entire 


T.PN: 


V.PN: 


11.PN. 


Flo.  M.— FertUiMtion  of  ovum  of  a  moUuik  (Etaiia  viritiii).  A.  Ovum  Dending  up  a  protu- 
berance to  meet  the  apermatoaoOn.  B.  Aniraaoh  oii'  nmle  pronucleus  to  meet  the  female 
pronucleus.    F.  PS,  female  pronucleua ;  m.PIf,  male  pronucleus ;  8,  BpermatozoOo. 


ovum.  The  resulting  union  gives  rise  to  the  new  nucleus  {seg- 
mentation nucleus),  which  is  to  control  the  future  destinies  of 
the  cell ;  while  the  cell  itself,  the  fertilized  ovum  {oosperm), 
enters  upon  new  and  marvelous  changes. 

In  reality  this  process  was  foreshadowed  in  the  dim  past  of 
the  history  of  living  things  by  the  conjugation  of  infusoria 
and  kindred  animal  and  vegetable  forms.  When  lower  forms 
(unicellular)  conjugate  they  become  somewhat  amoeboid  sooner 


REPRODUCTION. 


63 


)ment  may 

nucleus  of 
es  the  head 
Lmportance 

ing  its  way 
^h  a  special 
at — as  it  is 

the  mem- 
nues  active 

enters  and 
rhe  nucleus 
f  the  ovum 
leus  of  the 
pecial  func- 
>rrect  to  say 
ually  f  ertil- 
3ther  which 
levelopment 
niideus),  on 
it  amseboid, 
y  the  entire 


-M.PN. 


mding  up  a  protu- 
to  meet  the  female 
permatozotio. 


nucleus  {seg- 
I  destinies  of 
[Q  {p6spemi), 

dim  past  of 

of  infusoria 

lower  forms 

oeboid  sooner 


or  later,  and  division  of  cell  contents  results.  In  some  cases 
(septic  monads)  the  resulting  cell  may  burst  and  give  rise  to  a 
shower  of  animal  dust  visible  only  by  the  highest  powers  of  the 
microscope,  each  particle  of  which  proves  to  be  the  nucleus 
from  which  u  future  ".ndividual  arises. 

The  study  of  reproduction  thus  establishes  the  conception  of 
a  unity  of  method  throughout  the  animal  and,  it  may  be  added, 
the  vegetable  kingdom,  for  reproduction  in  plants  is  la  all  main 
points  parallel  to  that  process  in  animals. 

But  why  that  costly  loss  of  protoplasm  by  polar  globules  ? 
For  the  present  we  shall  only  say  that  it  appears  necessary  to 
prevent  parthenogenesis ;  or  at  least  to  balance  the  share  which 
the  male  and  female  elements  take  in  the  work  of  producing  a 
new  creature.  It  is  to  be  remembered  that  both  the  male  and 
female  lose  much  in  the  process — blood,  nervous  energy,  etc.,  in 
the  case  of  the  female,  while  the  male  furnishes  a  thousand-fold 
more  cells  than  are  used.  But  the  period  when  organisms  are 
best  fitted  for  reproduction  is  that  during  which  they  are  also 
most  vigorous,  and  can  best  afford  the  superfluous  drain  on 
their  energies. 

Segmentation  and  Subsequent  Changes. 

After  the  changes  described  in  the  last  chapter  a  new  epoch 
in  the  biological  history  of  the  ovum — now  the  odsperm  (or  fer- 
tilized egg) — begins.  A  very  distinct  nucleus  {segmentation 
nucleus)  again  appears,  and  the  cell  assumes  a  circular  outline. 
The  segmentation  or  division  of  the  ovum  into  usually  fairly 
equal  parts  now  commences.  This  process  can  be  best  watched 
in  the  microscopic  transparent  ova  of  aquatic  animals  which 
undergo  perfect  development  up  to  a  certain  advanced  stage 
in  the  ordinary  water  of  the  ocean,  river,  lake,  etc.,  in  which 
the  adult  lives. 

Segmentation  among  invertebrates  will  be  first  studied,  and 
for  this  purpose  an  ovum  in  which  the  changes  are  of  a  direct 
and  uncomplicated  nature  will  be  chosen. 

The  following  figures  and  descriptions  apply  to  a  mollur,k 
( Elysia  viridis) .  We  distinguish  in  ova  resting  stages  and  stages 
of  activity.  It  is  not,  however,  to  be  supposed  that  absolute 
rest  ever  characterizes  any  living  form,  or  that  nothing  is  tran- 
H^uring  because  all  seems  quiet  in  these  little  biological  worlds ; 
for  we  have  already  seen  reason  for  believing  that  life  and  in- 
cessant molecular  activity  nre  inseparable.    It  may  be  that,  in 


64 


ANIMAL  PHTSIOLOOT. 


the  case  of  resting  ova,  changes  of  a  more  active  character  than 
usual  are  going  on  in  their  molecular  constitution ;  but,  on  the 
other  hand,  there  may  be  really  a  diminution  of  these  activities 
in  correspondence  with  the  law  of  rhythm.  This  seems  the 
more  probable.    The  meaning,  however,  of  a  "  resting  stage  "  is 


m 


Fio.  ST.— PrimltiTe  egn  of  Tarioua  •nlnwh.  pwrfofmlng  MMBboid  movMnenU  (verr  much 

All  pniDitlve  eras  kre  naked  oella,  oapwle  of  dwnge  of  form.    Within  the 

■  ■   ■  ■  ■""  "         ■  .    .  -  iMmel  (the  Rwin- 


piw>piMm  (ec^jrelk)  Um  •  Im^  TMicttlar   .       

r  k  •  nuckoliM  (germ-uiot);  in  the  nuoleohM  •  germ-poliit  (nucleo- 


enUrned). 

lUrli.  flndy  muiulated  , 

vesicle),  and  in  the  latter  I  ..  _        . 

linua)  H  otten  Tldble.    Fig.  A  t—A  4,  Tbm  primitiTe  egg  ol  a  ohalk  qxHiKe  (LeMeulmii 

fMnut),  In  four  oonwoutire  conditions  of  motkm.    Fig.  B  l—B  8.  The  primitive  en  of  a 

hermitHsrab  (Chimdmeanthu*  eomutu»).  In  eight  oonseoutiTe  conditfcms  of  moUoa  (after 

B.  Van  Beneden).    Fig.  C  1— C  S.  PrimMve  ent  of  a  cat,  in  tour  dilferent  oooditlons  of 

moUon  (after  PAOger).    Fig.  i>.  PrtanitlTe  egg  of  a  trout.    Fig.  X.  PrimitlTe  egg  of  a  hen. 

Fig.  F.  PrtanUlTe  human  egg.   (Haeckel.) 

the  obvious  one  of  apparent  quiescence— cessation  of  all  kinds 
of  movement.  Then  ensues  rapidly  and  in  succession  the  fol- 
lowing series  of  transformations :  The  nucleolus  divides,  later 


EEPRODUCTION. 


66 


racter  than 
but,  on  the 
e  activities 
seems  the 
g  stage  "  is 


the  nucleus,  into  two  parts.    These  new  nuclei  then  wander 
away  from  each  other  in  opposite  directions,  and,  losing  their 


menta  (Tery  mncb 
fonn.  WlUiiii  the 
kernel  (the  Renn- 
[erm-poiiit  (nudeo- 
■ponKe  {btuimlmli 
primttlTe  egc  of  • 
M  of  motioa  (after 
went  oondittona  of 
>tU*e  em  of  •  hen. 


of  all  kinds 
Bsion  the  f  ol- 
divides,  later 


Fio.  68.— Karir  etagee  of  Msmentation  of  a  moUtiak,  SlyHa  vMdia  (drawn  from  the  IlTlng 
esg).  A,  oosperm  in  ataie  of  reat  after  the  eztraoion  of  the  pcdar  cells ;  B,  the  nuoleolua 
atone  baa  divided ;  O,  the  nucleus  is  diyiding ;  D,  the  nucleus,  as  such,  nas  disappeared, 
first  segmentation  furrow  appears ;  E,  later  stase ;  F,  ofiqierm  divided  into  two  distinct 
seKmentation  spheres,  the  clear  nuclear  space  m  the  center  of  the  aster  of  granules  is 
growbiflr  larow ;  O,  resting  stan  of  appressed  two  spheres ;  H,  I,  similar  stages  in  the 
produraon  of  four  spheres ;  K,  larmatfDn  of  eight-celled  stage.    (Haddon.) 

character  as  nuclei  and  nucleoli,  are  replaced  by  asters  (polar 
stars),  which  seem  to  arise  in  the  protoplasm  of  the  body  of 
the  cell,  and  which  are  in  close  juxtaposition  at  first,  but  later 
separate,  the  oosperm  becoming  amoeboid  in  one  region  at 
least.  A  groove,  which  gradually  deepens,  appears  on  the  sur- 
face, and  finally  divides  the  cell  into  two  halves,  which  at  once 
become  flattened  against  each  other.  The  nucleus  may  again 
be  recognized  in  the  center  of  each  polar  star,  while  a  new  nu- 
cleolus also  reappears  within  the  nucleus,  when  again  a  brief 
period  of  rest  ensues.  In  the  division  and  oioiination  of  the 
nucleus,  when  most  complicated  (karyokinesis),  the  changes 
may  be  generalized  as  consisting  of  division,and  segregation, 
followed  by  aggregation. 

The  subdivision  (aegmentaiion)  of  the  cell,  after  the  quies- 
cence referred  to,  again  commences,  but  in  a  plane  at  right 
angles  to  the  first,  from  which  four  spheres  result,  again  to  be 
followed  by  the  resting  stage.  The  process  continues  in  the . 
same  way,  so  that  there  is  a  progressive  increase  in  the  num- 
ber of  segments,  at  least  up  to  the  point  when  a  large  number 
s 


h  I 


ee 


ANIMAL  PHT8I0L00Y. 


has  been  formed.  This  is  rather  to  be  considered  as  a  type  of 
one  form  of  segmentation  than  as  applicable  to  all,  for  even 
at  this  early  stage  differences  are  to  be  noted  in  the  mode  of 
segmentation  which  characterize  effectually  certain  groups  of 
animals ;  but  in  all  there  is  segmentation,  and  that  segmenta- 
tion is  rhythmical. 


Fie.  ao.— The  dMTMja  of  •  trog't  cfi 
flrat  cleKTjyaeorifi ;  C,  4  celM ;  D, 


(10  ttaiM  eiilM||«d).    A,  the  pM«nt«eU ;  B,  the  two 
oelk(4aidiiuaMid4Te(ietatiTe);  £;  It  oella  (8  animal 


and  4  TeKeiaUre) :  jr.  M  oelli  (8  animal  and  8  Tegetative) ;  O,  M  oella  (10  animal  and  8 
vegetaUve):  H.  «>  onlla;  /,48  oelto;  K,  64  oella;  2.,  W  alean«eHiella ;  Ji;  —    ' 
odbdlB  animal  and  MvegetaUve).    (HaeckeL) 


Segmentation  results  in  the  formation  of  a  multicellular 
aggregation  which,  sooner  or  later,  incloses  a  central  cavity 
{segmentcUion  cavity,  blastocele).  Usually  this  cell  aggrega- 
tion {blaatvia,  blastosphere)  is  reduced  to  a  single  layer  of  in- 
vesting cells. 

The  GMtruIa. — Ensuing  on  the  changes  just  described  are 
others,  which  result  in  the  formation  of  the  gastrula,  a  form  of 
cell  aggregation  of  great  interest  from  its  resemblance  to  the 
Hydra  and  similar  forms,  which  constitute  in  themselves  inde- 
pendent animals  that  never  pass  beyond  that  stage.  The  blas- 
tula  becomes  flattened  at  one  pole,  then  r*  ^pressed,  the  cells  at 


.  as  a  type  of 
all,  for  even 
the  mode  of 
ain  groups  of 
lat  segmenta- 


u«ntH>eU ;  B,  the  two 
);  £,Uoelki (8 animal 
celto  (IS  MiUnal  Mid  8 


ft  multicellular 

central  cavity 

I  cell  aggrega- 

ffle  layer  of  in- 

b  described  are 
trula,  a  form  of 
mblance  to  the 
lemselves  inde- 
»ge.  The  bias- 
sed, the  cells  at 


I 


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m 
iiii 


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J  *•  *4  a  >•  a  '^p  ^  .."s  •-  fc  y  a  jp 


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IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


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Photographic 

Sciences 

Corporation 


23  WIST  MAIN  STRICT 

WIBSTCR.N.Y.  14S80 

(716)  S72-4S03 


ssM^i^'sm^^^^'^^i^'^^^^^^^'^^^^^^^^^^^'-*^^^*^*'^^^ 


*' 


CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICMH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microreproductions  /  Instltut  Canadian  de  microreproductions  historiques 


:V 


^S^fPSf^Sf 


REPKODUCTION. 


67 


this  region  becoming  more  columnar  (histological  differentia- 
tion).   This  depression  {invagination)  deepens  until  a  cavity  is 


Fio.  TO.-Blaatulft  and  gastrula  of  amphioxus  (Claus,  after  Hatschek).  A,  bl^tula  with  flat- 
tened lower  poJe  of  brger  cells ;  B,  commenclne  invaKinatipn ;  C,  gaBtnUatlon  completedi; 
the  blastopore  is  stlU  widely  open,  and  one  of  flie  two  hinder-pole  mesoderm  cells  Is  seen 
at  its  ventral  Up.    The  cilia  of  the  epiblast  cells  are  not  represented. 

formed  (as  when  a  hollow  rubber  ball  is  thrust  in  at  one  part 
till  it  meets  the  opposite  wall),  in  consequence  of  which  a  two- 
layered  embryo  results,  in  which  we  recognize  the  primitive 
ifaouth  {blastopore)  and  digestive  cavity  {archenteron),  the 
outer  layer  {ectoderm)  being  usually  separated  from  the  inner 
{endoderm)  by  the  almost  obliterated  segmentation  cavity. 
Such  a  form  may  be  provided  with  cilia,  be  very  actively  loco- 
motive, and  bear,  consequently,  the  greatest  resemblance  to  the 
permaiient  forms  of  some  aquatic  animals. 

The  changes  by  which  the  segmented  oosperm  becomes  a 
gastrula  are  not  always  so  direct  and  simple  as  in  the  above- 
described  case,  but  the  behavior  of  the  cells  of  the  blastosphere 
may  be  hampered  by  a  burden  of  relatively  foreign  matter,  in 
the  form  of  food-yelk,  in  certain  instances ;  so  much  so  is  this 
the  case  that  distinct  modes  of  gastrula  formation  may  be  rec- 
ognized as  dependent  on  the  quantity  and  arrangement  of  food- 
yelk.  These  we  shall  pass  by  as  being  somewhat  too  compli- 
cated for  our  purpose,  and  we  return  to  the  egg  of  the  bird. 

The  Hen'i  Egg.— By  far  the  larger  part  of  the  hen's  egg  is 
made  up  of  yelk ;  but  just  beneath  the  vitelline  membrane  a 
small,  circular,  whitish  body,  about  four  millimetres  in  diame- 
ter, which  always  floats  uppermost  in  every  portion  of  the  egg, 
may  be  seen.  This  disk  {blastoderm,  cicatricula)  in  the  fertilized 
egg  presents  an  outer  white  rim  {area  ojpaca),  within  which  is 
a  transparent  zone  {area  peUmida),  and  most  centrally  a  some- 
what elongated  structure,  which  marks  off  the  future  being 
itself  {embryo).  All  of  these  parts  together  constitute  that  por- 
tion {blastoderm)  of  the  fowl's  egg  which  is  alone  directly  con- 
cerned in  reproduction,  all  the  rest  serving  for  nutrition  and 


68 


ANIMAL  PHYSIOLOay. 


protection.    The  appearance  of  relative  opacity  in  some  of  the 
parts  marked  off  as  above  is  to  be  explained  by  thickening  in 

the  cell-layers  of  which  they  are 
composed. 

The  Origin  of  the  Fowl'i  Egg.— 
The  ovary  of  a  young  but  mature 
hen  consists  of  a  mass  of  connect- 
ive   tissue    {stroma),    abundantly 
supplied  with  blood-vessels,  from 
which   hang  the  capsules  which 
contain  the  ova  in  all  stages  of 
development,  so   that   the   whole 
suggests,  but  for  the  color,  a  bunch 
of  grapes  in  an  early  stage.    The 
ovum  at  first,  in  this  case  as  in  all 
others,  a  single  cell,  becomes  com- 
plex by  addition  of  other  cells  {dis- 
cus proligerus,  etc.),  which  go  to 
make  up  the  yelk.    All  the  other 
parts  of  the  hen's  egg  are  additions 
made  to  it,  as  explained  before,  in 
its  passage  d(>wn  the  oviduct.    The 
original  ovum  remains  as  the  blas- 
toderm, the  segmentation  of  which 
may  now  be  described  briefly,  its 
character  being  obvious  from  an 
examination  of  Fig.  72,  which  rep- 
resents a  surface  view  of  the  seg- 
menting fertilized  ovum  {oosperm). 
A  segmentation  cavity  appears 
early,  and  is  bounded  above  by  a 
single  layer  of  epiblast  cells  and 
below  by  a  single  layer  of  primi- 
tive hypoblast  cells,  which  latter 
is  soon  composed  of  several  layers, 
Fia.  n.-FernliT^newUve  organs  of  while  the  Segmentation  cavity  dis- 

toeJowKalter  D«ltoii)^^;^ovarjrj    appears. 


B,  OrawiUui  follicle,  from  which  the 
«m  haa  juBt  been  diMsharged  ;  C. 
yeBt,  enterinKupper  extremity  of 
oviduct  ;  D,  £,  second  portion  of 
oviduct,  in  which  the  chalaalferous 
membrane,  chatazn,  and  albumen 
are  formed  ;  F,  third  portion,  In 
which  the  fibrous  shell  membranes 
are  produced ;  G,  fourth  portion  laid 

open,  showing  the  egg  completely  cells,  arranged  irregularly  and  ly^ 

formed  with  lis  calcareous  shell ;  rt,  '         ,       .       ,,  -n  >'j.    i. 

canal  through  which  the  egg  is  ex-    mg  loOSely  in  the  yelk,  COUStltUt 


The  blastoderm  of  an  unincu- 
bated"  but  fertilized  egg  consists 
of  a  layer  of  epiblastic  cells,  and 
beneath  this  a  mass  of  rounded 


REPRODUCTION. 


69 


y  in  some  of  the 

t)y  thickening  in 

which  they  are 

he  Fowl's  £gg.— 

»ung  but  mature 
mass  of  connect- 
na),    abundantly 
)od-vessels,  from 
capsules  which 
in  all  stages  of 
that   the   whole 
he  color,  a  bunch 
jarly  stage.    The 
this  case  as  in  all 
)11,  becomes  com- 
f  other  cells  (dis- 
tc),  which  go  to 
c.    All  the  other 
egg  are  additions 
plained  before,  in 
the  oviduct.    The 
nains  as  the  blas- 
sntation  of  which 
:;ribed  briefly,  its 
obvious  from  an 
'ig.  72,  which  rep- 
view  of  the  seg- 
1  ovum  {oosperm), 
m  cavity  appears 
nded  above  by  a 
spiblast  cells  and 
e  layer  of  primi- 
ells,  which  latter 
of  several  layers, 
itation  cavity  dis- 

rm  of  an  unincu- 
ized  egg  consists 
iblastio  cells,  and 
mass  of  rounded 
rregularly  and  ly- 
le  yelk,  constitut- 


Fio.  7«.-VariouB  -tages  In  the  aeRmentation  of  a  fowl's  egg  tKOUlker). 

inir  the  primitive  hypoblast.  After  incubation  for  a  couple  of 
hours  these  cell,  become  differentiated  into  a  lower  layer  of 
mZ^ZulnypoUa^t),  with  -soblastic  c^ls  sc^^^^^^^^  be 
tween  the  epiblast  and  hypoblast.  It  is  noteworthy  that,  m  the 
S  segmentation  will  proceed  up  to  a  certain  stage  mdepen- 
Sy  of  the  advent  of  the  male  cell,  apparently  indicating  a 
tendency  to  parthenogenesis. 


Fm  78  -Portion  of  aeoUon  through  an  unlncubjOed  fowl>  o^JP™  (»J^'  iS?w  la^r^wU^Sf 


70 


ANIMAL  PHYSIOLOGY. 


The  fowl's  ovum  then  belongs  to  the  class,  a  portion  of  which 
alone  segments  and  develops  into  the  embryo  {meroblastic),  in 
contradistinction  to  what  happens  in  the  mammalian  ovum,  the 
whole  of  which  undergoes  division  {holoblastic) ;  a  distinction 
which  is,  however,  superficial  rather  than  fundamental,  for  in 
reality  in  the  fowl's  egg  the  whole  of  the  original  ovum  does 


eet. 


''^■\ 


*p. 


FiQ.  74.-SectloM  of  ovum  of  a  rabbit.  HluBtratlnft  fprmatton  o' tj*  P^J*Slt.7^'L^^  ^^, 
E  VmBeneden).  A,  B,  0,  D.  are  ova  to  Mcoessive  sUges  of  dewtopment.  «p,  »oiia  peUu- 
clda ;  eet,  ectomeres,  or  outer  celta ;  ent,  entomeres,  or  toner  oeUa. 

segment.  This  holoblastic  character  of  the  mammalian  ovum 
and  its  resemblance  to  the  segmentation  of  those  invertebrate 
forms  previously  described  may  become  apparent  from  an  ex- 
amination of  the  accompanying  figures. 

We  shall  return  to  the  development  of  the  mammalian  ovum 
later ;  in  the  mean  time  we  present  the  main  features  of  devel- 
opment in  the  bird. 

Remembering  that  the  development  of  the  embryo  proper 
takes  place  within  the  pellucid  area  only,  we  point  out  that  the 
area  opaca  gradually  extends  over  the  entire  ovum,  inclosing 


immalian  ovum 
jse  invertebrate 
3nt  from  an  ex-  , 

ammalian  ovum 
jatures  of  devel- 

( embryo  proper 
lint  out  that  the 
ovum,  inclosing 


REPRODUCTION. 


71 


the  yelk,  so  that  the  original  disk  which  lay  like  a  watch-glass 
on  the  rest  of  the  ovum,  has  grown  into  a  sphere.  That  portion 
ijf  this  area  nearest  the  pellucid  zone  {area  vasctdosa)  develops 


H- 


Fio.  75.— Dlagraminatic  transverse  sections  through  a  hjrpothetical  nuunmal  oosperm  (Had- 
don).  A.  The  yelk  of  the  prlmitiTe  mammalian  oOsperm  is  now  lost.  B.  Later  stage ; 
the  non-embrronic  epiblast  nas  grown  over  the  emiwyonic  area  to  form  the  covering  cells. 
ep,  epiblast  of  embryo ;  ep',  epiblast  of  yelk-sac ;  Ay,  primitive  hypoblast ;  y. «,  yelk-sac, 
or  blastodermic  vesicle. 

blood-vessels  that  derive  the  food-supplies,  which  replenish  the 
blood  as  it  is  exhausted,  from  the  hypoblast  of  the  area  opaca. 

The  first  indications  of  future  structural  outlines  in  the 
embryo  is  the  formation  of  the  primitive  streak,  an  opaque  band 
in  the  long  diameter  of  the  pellu- 
cid area,  opaque  in  consequence 
of  cell  accummulation  in  that  re- 
gion. Very  soon  a  groove  {primi- 
tive groove)  extends  throughout 
this  band,  which  gradually  occu- 
pies a  more  central  position.  The 
relative  thickness  of  the  several 
parts  and  the  arrangement  of  cells 
may  be  gathered  from  Fig.  76. 
These  structures  are  only  tempo- 
rary, and  those  that  replace  them 
will  be  described  subsequently. 

We  have  thus  far  spoken  of 
cells  as  being  arranged  into  epi- 
blast, hypoblast,  and  mesoblast. 
The  origin  of  the  first  two  has 
been  sufficiently  indicated.  The 
mesoblast  forms  the  intermediate 
germinal  layer,  and  is  derived 
from   the   primitive    hypoblast, 

which  diflferentiates  into  a  stratum  of  flattened  cells,  situated 
below  the  others,  and  constituting  the  later  hypoblast,  and  in- 


Fio.  78.— Surface  view  of  pellucid  area  of 
blastoderm  of  eighteen  hours  ( Foster  and 
Balfour).  H,  medullary  folds;  tnc,  med- 
ullary groove ;  pr,  primitive  groove. 


72 


ANIMAL  PHYSIOLOGY. 


termediate  less  closely  arranged  cells,  termed,  from  their  posi- 
tion, mesoblast. 

It  will  be  noticed  that  all  future  growth  of  the  embryo  be- 
gins axially,  at  least  in  the  early  stages  of  its  development. 

Ae  the  subsequent  growth  and  advance  of  the  embryo  de- 
pend on  an  abundant  and  suitable  nutritive  supply,  we  must 
now  turn  to  those  arrangements  which  are  temporary  and  of 
subordinate  importance,  but  still  for  the  time  essential  to  devel- 
opment. 

Embryonic  Membranes  of  Birds. 

It  will  be  borne  in  mind  throughout  that  the  chief  food-sup- 
ply for  the  embryo  bird  is  derived  from  the  yelk ;  and,  as  would 


1"*..        -^ 


FioB  '.7-n.—A  aeriea  of  diMtnuna  Intended  to  facilitate  the  comprehenaion  of  the  relation*  of 
the  membrane*  to  other  parts  (after  Foster  and  Balfom-).  A,  B,  C,  D,  E,  F  are  vertical 
gections  in  the  lone  axis  of  the  embryo  at  different  periods,  showing  the  stages  of  devel(n>- 
ment  of  the  amnion  and  of  the  yellc-gac.  I,  U,  lU,  IV  are  transverse  sections  at  about  the 
same  stages  of  development.  1,  ii,  ill,  posterior  part  of  longitudinal  section,  to  Ulustrate 
three  stages  in  formation  of  the  allantois.  e,  embryo ;  »,  yelk ;  pp,  pleuroperitoneal  cav- 
ity ;  vfT^telline  membrane  of  anmiotic  fold ;  ol,  allantois ;  a,  amnion ;  a',  aUmentaiy 


i 


be  expected,  the  older  the  embryo  the  smaller  the  yelk,  or,  as  it 
is  now  called  when  limited  by  the  embryonic  membranes,  the 
yelksac  {umbilical  vesicle  of  the  mammalian  embryo).  The 
manner  in  which  this  takes  place  will  appear  upon  an  inspec- 
tion of  the  accompanying  figures. 

Very  early  in  the  history  of  the  embryo  two  eminences,  the 
head  and  the  tail  folds,  arise,  and,  curving  over  toward  each 


fe^'j 


ifWiiiflfifltill^ 


from  their  posi- 

:  the  embryo  be- 
evelopment. 
f  the  embryo  de- 
supply,  we  must 
emporary  and  of 
ssential  to  devel- 


le  chief  f  ood-sup- 
k;  and,  as  would 


ension  of  the  relatioiw  of 
B,  C,  D,  E,  F  are  vertical 
iog  the  stages  of  develop- 
erae  sections  at  about  the 
linal  section,  to  illustrate 
pp,  pleuroperitoneal  cav- 
amnion ;  a',  aUmentaiy 


the  yelk,  or,  as  it 
B  membranes,  the 
n  embryo).  The 
■  upon  an  inspec- 

vo  eminences,  the 
)ver  toward  each 


78 


74 


ANIMAL  PHYSIOLOGY. 


other,  meet  after  being  joined  *by  corresponding  lateral  folds. 
Fusion  and  absorption  result  at  this  meeting-point,  in  the 
inclosure  of  one  cavity  and  the  blending  of  two  othere.    These 


>r.e. 


v. 


Fio.  80.  —Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo  chick  (after  Foster 
and  Balfour).  iV.  C,  Neural  canal ;  Ch,  notocbord  ;  Fg,  foregut ;  T.  So,  somatc^leure ; 
F.  Sp,  splancbnopleure ;  S!p,  splancbnopleure,  forming  lower  wall  of  foregut ;  Bt,  heart ; 
pp,  pleuroperitoneal  cavity ;  Am,  amniotic  fold ;  £,  epiblaat ;  M,  mesobh.st ;  H,  hypoblast. 

folds  constitute  the  amniotic  membranes,  the  inner  of  which 
forms  the  true  amnion,  the  oater  the  false  amnion  {serotis  mem- 
brane, suhzonal  membrane).  Within  the  amnion  proper  is  the 
amniotic  cavity  filled  with  fluid  {liquor  amnii),  while  the  space 
between  the  true  and  false  amniotic  folds,  which  gradually  in- 
creases in  size  as  the  yelk-sac  diminishes,  forms  the  pleuro- 
peritoneal cavity,  body  cavity,  or  ccelom.  The  amniotic  cavity 
also  extends,  so  that  the  embryo  is  surrounded  by  it  or  lies 
centrally  within  it.  The  enlargement  of  the  ccelom  and  exten- 
sion of  the  false  amniotic  folds  lead  finally  to  a  similar  meeting 
and  fusion  like  that  which  occurred  in  the  formation  of  the  true 
amniotic  cavity.  The  yelk-sac,  gradually  lessening,  is  at  last 
withdrawn  into  the  body  of  the  embryo. 

Fig.  80  shows  how  the  amniotic  head  fold  arises,  from  a 
budding  out  of  the  epiblast  and  mesoblast  at  a  point  where  the 
original  cell  layers  of  the  embryo  have  separated  into  two  folds, 
the  somatopleure  or  body  fold  and  the  splanchnopleure  or  vis- 
ceral fold,  owing  to  a  division  or  cleavage  of  the  mesoblast 
toward  the  long  axis  of  the  body.  Remembering  this,  it  is 
always  easy  to  determine  by  a  diagram  the  composition  of  any 
one  of  the  membranes  or  folds  of  the  embryo,  for  the  compo- 
nents must  be  epiblast,  mesoblast,  or  hypoblast ;  thus,  the 
splanchnopleure  is  made  up  of  hypoblast  internally  and  meso- 
blast externally — a  principle  of  great  significance,  since,  as  will 
be  learned  later,  all  the  tissues  of  the  body  may  be  classified 
simply,  and  at  the  same  time  scientifically,  according  to  their 
embryological  origin. 


yfffMWffiiiiiiiipiiiiffi 


^I^W^SSlW^^ 


w^ms^H^m 


wmm  ■- 


REPRODUCTION. 


w 


xg  lateral  folds. 

g-point,  in  the 

othei's.    These 


Inyo  chick  (after  Foster 
;  F.  So,  gonwtt^leure ; 
of  foregut ;  Ht,  heart ; 
isobh  at ;  H,  bypoUaat. 


inner  of  which 
yn  (serotts  mern- 
on  proper  is  the 
while  the  space 
h  gradually  in- 
•ms  the  pleuro- 
amniotic  cavity 
id  by  it  or  lies 
elom  and  exten- 
similar  meeting 
ation  of  the  true 
aning,  is  at  last 

I  arises,  from  a 
point  where  the 
d  into  two  folds, 
.nopleure  or  vis- 

the  mesoblast 
Bring  this,  it  is 
iposition  of  any 

for  the  compo- 
>last;  thus,  the 
daily  and  meso- 
ce,  since,  as  will 
lay  be  classified 
wording  to  their 


The  allantois  is  a  structure  of  much  physiological  impor- 
tance.  It  arises  at  the  same  time  as  the  amniotic  folds  are 
forming,  by  a  budding  or  protrusion  of  the  hind-gut  into  the 


m,  position  of  the  mouth ;  me,  mesentery. 

pleuro-peritoneal  cavity,  and  hence  consists  of  an  outgrowth 
of  mesoblast  lined  by  hypoblast.  .  ,    ^,         , 

The  outer  membrane  of  the  allantois  fuses  with  the  subzo- 
ncd  (serous)  membrane,  and,  with  the  latter  extendmg  beyond 
the  yelk-sac,  incloses  the  albumen  of  the  egg  in  a  space  termed 


E-  -^=SM,v.  m. 


brane. 


.;-1 


76 


ANIMAL  PHYSIOLOGY. 


the  jUacenial  sac  by  Duval,  who  has  recently  described  this  pro- 
cess. Villi,  or  tubular  vascular  outgrowths,  spring  from  the 
lining  of  this  sac  and  serve  to  convey  the  absorbed  and  prob- 
ably altered  albumen  to  the  embryo,  in  which  process  of  vas- 
cular transport  of  nourishment  the  yelk-sac,  that  also  abounds 
in  blood-vessels  as  well  as  the  allantois,  takes  part.  The 
physiological  import  of  the  various  structures  above  described 
will  be  considered  more  fully  later.  At  this  point  a  compari- 
son of  the  formation  of  the  corresponding  parts  in  mammals 
will  be  undertaken. 

The  Fcetal  (Embryonic)  Membranes  of  Mammals. 

The  differences  between  the  development  of  the  egg  mem- 
branes of  mammals  and  birds  are  chiefly  such  as  result  from 


v 

p.am. 

rS 

r0.m.t). 

r  -0.9. 

-•.t. 

-am,' 

''\ 

-4a,. 

-^y 

U 

Vs 


Via.  88.  Flu.  84. 

Fio.  89.— Diagrammatio  looKitudlnal  aeotion  of  oOaperm  of  rabbit  at  an  advanced  Rtase  of 
pregnancy  (KOUiker,  after  Bischoff).  a,  amnion ;  al,  allantolH  with  its  blood-veaseli ;  e, 
embryo ;  da,  yeUc^sac :  ed,  ed',  ed",  nypoblaatic  epithelium  of  the  yelk-sac  and  its  stalk 
(umbilical  vcMicle  and  cord) :  /d,  vascular  mesoblastic  membrane  of  the  umbilical  cord 
and  vesicle ;  p,  placental  villi  formed  by  the  allantois  and  subasonal  membrane  ;  r,  space 
filled  with  fluid  between  the  amnion,  the  allantois,  and  the  yelk-sac  ;  tt,  sinus  terminolis 
(marginal  vltelUoe  blood-vessel) ;  u,  urachus,  or  stalk  of  the  allantois. 

Fio.  81.— Diagrammatic  dorsal  view  of  an  embryo  rabbit  with  its  membranes  at  the  stage  of 
nine  sonutee  (Haddon,  after  Van  Beneden  and  Julin).  ai,  allantois,  showing  from  behind 
the  tail  fold  of  the  embryo ;  am.  anterior  border  of  true  amnion :  a.  t',  area  vasculosa,  the 
outer  border  of  which  indicates  the  farthest  extension  of  the  mesoblast ;  M,  blastoderm, 
here  consisting  only  of  epiblast  and  hypoblast ;  o.  m.  v.  omphalo-mesenterio  or  vitelline 
veins ;  p.  am,  proamnion ;  pi,  non-vascular  epiblastic  villi  of  the  future  placenta ;  «.  t,  si- 
nus terminalis. 

the  absence  in  the  former  of  an  egg-shell  and  its  membranes, 
and  of  yelk  and  albumen.  The  mammalian  ovum  is  inclosed 
by  a  zona  radiata  {zona  peUiuyida)  surrounding  another  very 
delicate  covering  (Fig.  58). 

The  growth  of  the  blastodermic  vesicle  (yelk-sac)  is  rapid. 


REPRODUCTION. 


77 


)scribed  this  pro- 
spring  from  the 
iorbed  and  prob- 
1  process  of  vas- 
hat  also  abounds 
ikes  part.  The 
above  described 
)oint  a  compari- 
rts  in  mammals 


Mammals. 

f  the  egg  mem- 
i  as  result  from 


and,  being  filled  with  fluid,  the  zona  is  thinned  and  soon  disap- 
pears. 

The  germinal  area  alone  is  made  up  of  three  layers  of  cells 
(Fig.  10-i),  the  rest  of  the  upper  part  of  the  oosperm  being  lined 
with  epiblast  and  hypoblast,  while  the  lower  zone  of  the  yelk- 
sac  consists  of  epiblast  only. 

Simple,  non-vascular  villi,  serving  to  attach  the  embryo 
to  the  uterine  walls,  usually  project  from  the  epiblast  of  the 
subzonal  membrane.  In  the  rabbit  they  do  not  occur  every- 
where, but  only  in  that  region  of  the  epiblast  beneath  which  the 
mesoblast  does  not  extend,  with  the  exception  of  a  patch  which 
soon  appears  and  demarkates  the  site  of  the  future  placenta. 

The  extension  of  the  mesoblast  takes  place  in  every  direction 
from  the  embryo  except  directly  around  the  head ;  but  the  two 


an  advanced  itase  of 
th  JU  blood-veflwfi ;  e, 
yelk-sac  and  ite  stalk 
of  the  umbilical  cord 
i  membrane  ;  r,  space 
c  ;  9t,  sinus  termlnalis 
Is. 

ibranes  at  the  staKe  of 
I  showing  from  behind 
t'j  area  vosculoaa,  the 
'Mast ;  M.  blastoderm, 
nesenterio  or  vitelline 
ture  placenta ;  1. 1,  si- 


ts  membranes, 

im  is  inclosed 

another  very 

-sac)  is  rapid. 


Fio.  85.— Diagrammatic  median  vertical  longitudinal  sections  through  embryo  rabbit  (Had- 
don,  after  Van  Beneden  and  Julin).  A.  Bection  through  embryo  of  Fig.  M.  B.  Section 
through  embryo  of  eleven  days,  at,  ollontois ;  am,  amnion ;  a.  nw,  anterior  median  plate 
of  mesoblast,  formed  by  the  junction  of  the  anterior  horns  of  the  area  opoca ;  a.  pi,  area 
placentalis ;  a.  v,  area  vaaculoaa ;  eft,  chorion ;  cce,  coelom  of  embryo ;  cae',  extra-embry- 
onic portion  of  the  body-cavity ;  ep,  epiblast ;  hy,  hypoblast ;  m.  unsplit  mesoblast ;  o.  a, 
orifice  of  amnion ;  p{,  placenta ;  pro.  a,  proamnion ;  «.  (,  sinus  termlnalis ;  v,  epiblostic 
vllU  of  blastodermic  veacle. 

expansions  of  the  mesoblast  which  mark  out  this  area  extend 
for  some  distance  in  front  of  the  head,  and  ultimately  unite ; 
so  that  immediately  in  front  of  the  head  there  is  a  circular 
region  in  which  the  blastoderm  consists  of  epiblast  and  hypo- 


r 


78 


ANIMAL  PHYSIOLOGY. 


blast  only,  forming  a  cavity  into  which  the  anterior  part  of  the 
embryo  early  projects  {pro-amn  'on). 

The  true  amnion  arises  only  from  the  posterior  end  of  the 
embryo,  and,  extending  over  in  a  forward  direction,  meets  the 
raised  projection  of  the  pro-amnion  with  which  it  fuses. 

The  amniotic  cavity  becomes  one  with  that  space  (extra-em- 
bryonic pleuro-peritoneal  cavity)  arising  from  the  cleavage  of 


Fio.  86.— Foetal  envelopes  of  a  rabbit  embryo  (Mlnot,  after  Van  Beneden  and  Julin).  Later 
stage  than  Fig.  85  B.  The  amnion  has  become  fused  with  the  blastoderm  in  front  of  the 
embryo,  and  Its  cavity  is  therefore  continnous  with  the  extra-embryonic  portion  of  the 
liody-cavity  in  front  of  the  embryo.  Al,  allantois ;  am,  amnion ;  am',  portion  of  the 
amnion  united  with  the  wbUs  of  the  allantois ;  A.pl,  area  placentalis ;  Av,  area  vasculoea ; 
Ch,  chorion ;  Cce,  coelom  or  body-cavity ;  Ca",  extra-embryo>:ic  portion  of  the  body- 
cavity  ;  Cael,  anterior  portion  of  the  same,  produced  by  the  fusion  of  the  cavity  of  the 
amnion  with  that  of  the  anterior  portion  of  the  area  opaca ;  Be,  epiblast ;  £ii,  alimentary 
canal  of  the  embryo ;  Bnt,  hypoblast ;  PI,  placenta ;  pro.  A,  proamnion ;  T,  sinus  ter- 
minalls :  V,  villi  of  blastodermic  vesicle ;  Y,  cavity  of  blastodermic  vesicle. 

the  mesoblast,  which  now  advances  beyond  the  head  of  the  em- 
bryo and  the  pro-amnion.  The  pro-amnion  by  gradual  atrophy 
gives  place  to  the  true  amnion. 

At  about  the  same  period  as  these  events  are  transpiring  the 
vascular  yelk-sac  has  become  smaller,  and  the  allantois  with  its 
abundant  supply  of  blood-vessels  is  becoming  more  prominent, 
and  extending  between  the  amnion  and  subzonal  membrane. 

The  formation  of  the  chorion  marks  an  important  step  in 
the  development  of  mammals  in  which  it  plays  an  important 
functional  part.  It  is  the  result  of  the  fusion  of  the  allantois, 
which  is  highly  vascular,  with  the  subzonal  membrane,  the  villi 
of  which  now  become  themselves  vascular  and  more  complex 
in  other  respects. 

An  interesting  resemblance  to  birds  has  been  observed  (by 
Osborn)  in  the  opossum.     When  the  allantois  is  small  the 


11^ 


REPRODUCTION. 


19 


iterior  part  of  the 

sterior  end  of  the 
•ection,  meets  the 
;h  it  fuses. 
t  space  (extra-em- 
a.  the  cleavage  of 


'\T. 


ineden  and  Julin).  Later 
blastoderm  in  front  of  the 
embryonic  portion  of  the 
ion ;  am',  portion  of  the 
talis ;  Av,  area  vasculosa ; 
i>:ic  portion  of  the  body- 
ision  of  the  cavity  of  the 
eptblast ;  £>i,  alimentary 
proamnion ;  T,  sinus  ter- 
nic  vesicle. 

e  head  of  the  em- 
r  gradual  atrophy 


re  transpiring  the 
allantois  with  its 
;  more  prominent, 
nal  membrane, 
important  step  in 
lays  an  important 
n  of  the  allantois, 
lembrane,  the  villi 
tid  more  complex 

3een  observed  (by 
tois  is  small  the 


Fio.  87.-Embryo  of  dog,  twenty-ilve  days  old,  opened  on  *'^^'^J'*^.J^i.^^,^7^' 
tral  walls  have  been  removed,  a,  nose-pits;  6.  eyes;  c,  un^CT-Jaw  (first  BUl-JJon) .. ». 
wcond  giU-arch ;  e./,  o,  h,  heart  (e,  rtehr,  /,  left  auricle;  ff.,riKht,  *;>«",  Ye«Si"l^.;^. 
i^  (orSin  of);  fclfc  liver  (in  the  miffdie  between  the  two  •»«^,w  ">«  ™*  y?*;J5,*£> 
I,  stonlacff ;  m.  intestine ;  n,  velk-mc  ;  o,  primUive  kidnejs ;  P.  o"«ntote  A**^"^^ 
i,  hind-Umbs.  The  crooked  embryo  has  been  stretched  straight.  vHaccKel,  alter 
Biachoir.) 


A.r^ 


Fio.  8B.— Diaxram  of  an  embryo  showing  the  relations  of  the  vascular  allantois  to  the  vlUi  of 
the  chorion  (Oadlat).  e,  embryo  lying  In  the  cavity  of  the  amnion ;  y»,  yelk-sac  j  al,  al- 
lantoto ;  A.  K,  allantolo  vessels  dipping  into  the  vUU  of  the  chorion ;  cA,  chorion. 


80 


ANIMAL  PHYSIOLOGY. 


blastodermic  vesicle  (yelk-sac)  has  vascular  villi,  which  in  all 
probability  not  only  serve  the  purpose  of  attaching  the  embryo 
to  the  uterine  wall  but  derive  nourishment,  not  as  in  birds,  from 
the  albumen  of  the  ovum,  but  directly  in  some  way  from  the 
uterine  wall  of  the  mother.    It  will  be  remembered  that  the 

opossum  ranks  low  in  the 
mammalian  scale,  so  that  this 
resemblance  is  the  more  signifi- 
cant from  an  evolutionary  point 
of  view. 

The  term  chorion  is  now  re- 
stricted to  those  regions  of  the 
Bubzonal  membrane  to  which 
either  the  yelk-sac  or  the  allan- 
tois  is  attached.  The  former 
zone  has  been  distinguished  as 
the  false  chorion  and  the  latter 

Fia.SB.-DiasrramofthefOBtalmembraiiMof     aS    the    true    chorion.       In    the 
the  Virginian  oposHum  (Haddon,  after  Os- 
born).    Two  villi  ar     " 


are  shown  greatly  en- 
larged .  The  ptoeeaaes  of  the  cells,  which 
have  been  exaggerated,  doubtless  corre- 
spond to  the  pieudopodia  described  by 
Caldwell,  al,  allantoi  i ;  am,  ainn'on ;  s.  t, 
sinus  terminalls  ;  a.  z,  subzonal  mem- 
brane ;  V,  villi  on  the  subzonal  membrane 
in  the  region  of  the  yelk-sac :  y«,  yelk 
The  vascular  splanchnopleure  (hy- 


6AC 

pol 
the 


nople       ,  , 
iblast  and  mesoblast)  is  indicated  by 


he  black  line. 


rabbit  the  false  chorion  is  very 
large  (Fig.  83),  and  the  (placen- 
tal) chorion  very  small  in  com- 
parison, but  the  reverse  is  the 
case  in  most  mammals.  It  will 
be  noted  that  in  both  birds  and 
mammals  the  allantois  is  a  nu- 
tritive organ.  Usually  the  more  prominent  and  persistent  the 
yelk-sac,  the  less  so  the  allantois,  and  vice  versa;  they  are 
plainly  supplementary  organs. 

The  Placenta. — This  structure,  which  varies  greatly  in  com- 
plexity, may  be  regarded  as  the  result  of  the  union  of  structures 
existing  for  a  longer  or  shorter  period,  free  and  largely  inde- 
pendent of  each  other.  With  evolution  there  is  differentiation 
and  complication,  so  that  the  placenta  usually  marks  the  site 
where  structures  have  met  and  fused,  differentiating  a  new 
organ;  while  corresponding  atrophy,  obliteration,  and  fusion 
take  place  in  other  regions. 

All  placentas  are  highly  vascular,  all  are  villous,  all  dis- 
charge similar  functions  in  providing  the  embryo  with  nourish- 
ment and  eliminating  the  waste  of  its  cell-life  (metabolism). 
In  structural  details  they  are  so  different  that  classifications  of 
mammals  have  been  founded  upon  their  resemblances  and  dif- 
ferences.   These  will  now  be  briefly  described. 

In  marsupials  the  yelk-sac  is  both  large  and  vascular ;  the 


REPRODUCTION. 


81 


which  in  all 

ig  the  embryo 

I  in  birds,  from 

way  from  the 

jered  that  the 

low    in    the 

,  so  that  this 

le  more  signifi- 

lutionary  point 

'on  is  now  re- 
regions  of  the 
rane  to  which 
ac  or  the  allan- 
The  former 
stinguished  as 
and  the  latter 
)rion.     In  the 
shorion  is  very 
nd  the  (placen- 
'■  small  in  com- 
reverse  is  the 
nmals.    It  will 
both  birds  and 
lantois  is  a  nu- 
persistent  the 
raa;  they  are 

reatly  in  com- 
n  of  structures 
I  largely  inde- 
diflFerentiation 
narks  the  site 
tiating  a  new 
n,  and  fusion 

lloiis,  all  dis- 
with  nourish- 
(metabolism). 
issifications  of 
ances  and  dif- 

vascular;  the 


allantois  small  but  vascular ;  the  former  is  said  (Owen)  to  be 
attached  to  the  subzonal  membrane,  the  latter  not ;  but  no  villi, 
and  consequently  no  true  chorion,  is  developed.  All  mammals 
other  than  the  monotremes  and  marsupials  have  a  true  allan- 
toic placenta. 

The  Diieoidal  Flftoenta.— This  form  of  placenta  is  that  existing 
in  the  rodentia,  insectivora,  and  cheiroptera.  The  condition 
found  in  the  rabbit  is  that  which  has  been  most  studied.  The 
relation  of  parts  is  shown  in  Fig.  83. 

The  uterus  of  the  rodent  is  two-homed ;  so  we  find  in  gen- 
eral several  embryos  in  each  horn  in  the  pregnant  rabbit.  They 
are  functionally  independent,  each  having  its  own  set  of  mem- 
branes. It  will  be  observed  from  the  figure  that  the  true  vil- 
lous chorion  is  confined  to  a  comparatively  small  region ;  there 
is,  however,  in  addition  a  false  chorion  without  villi,  but  highly 
vascular.  This  blending  of  forms  of  placentation  which  exist 
separately  in  different  groups  of  animals  is  significant.  In  the 
rabbit,  at  a  later  stage,  there  is  considerable  intermingling  of 
foetal  and  maternal  parts. 

The  Metadiieoidal  Pkoenta.  —  This  type,  which,  in  general 
naked-eye  appearances,  greatly  resembles  the  former,  is  found 
in  man  and  the  apes.  The  condition  of  things  in  man  is  by  no 
means  as  well  understood  as  in  the  lower  mammals,  especially 
in  the  early  stages ;  so  that,  while  the  following  account  is  that 
usually  given  in  works  on  embryology,  the  student  may  as  well 
understand  that  our  knowledge  of  human  embryology  in  the 
very  earliest  stages  is  incomplete  and  partly  conjectural.  The 
reason  of  this  is  obvious :  specimens  for  examination  depending 
on  accidents  giving  rise  to  abortion  or  sudden  death,  often  not 
reaching  the  laboratory  in  a  condition  permitting  of  trust- 
worthy inferences. 

It  is  definitely  known  that  the  ovum,  which  is  usually  fer- 
tilized in  the  oviduct  (Fallopian  tube),  on  entering  the  uterus 
becomes  adherent  to  its  wall  and  encapsuled.  The  mucous 
membrane  of  the  uterus  is  known  to  undergo  changes,  its  com- 
ponent parts  increasing  by  cell  multiplication,  becoming  in- 
tensely vascular  and  functionally  more  active.  The  general 
mucous  surface  shares  in  this,  and  is  termed  the  decidua  vera  j 
but  the  locality  where  the  ovum  lodges  is  the  seat  of  the  great- 
est manifestation  of  exalted  activity,  and  is  termed  the  decidua 
serotina;  while  the  part  believed  to  have  invested  the  ovum  by 
fused  growths  from  the  junction  of  the  decidua  vera  and  sero- 
tina is  the  decidua  reflexa. 

6 


82 


ANIMAL  PHYSIOLOGY. 


The  decidua  serotina  and  reflexa  thus  become  the  outermost 
of  all  the  coveriijgs  of  the  ovum.  These  and  some  other  devel- 
opments are  figured  below.  It  is  to  be  remembered,  however, 
that  they  are  highly  diagrammatic,  and  represent  a  mixture 


Fio.  M.  -Series  of  dlagrama  ivpreaenttaig  the  relattona  of  the  deckliut  to  the  oturi.  at  different 

r9riods,  in  the  human  aubject.  The  decidua  are  darlc,  tlie  ovum  aliaded  tranaveraely.  In 
and  5  the  chorionic  Toacuiar  proceaaes  are  figured  (after  Dalton).  1.  Ovum  reatins  on 
the  decidua  aerotina ;  S.  Decidua  reilexa  growing  round  the  ovum ;  8.  Completion  of  the 
decidua  around  the  ovum  ;  4.  Villi,  growing  out  all  around  the  chorion ;  S.  The  villi,  spe- 
cially developed  at  the  site  of  the  future  placenta,  having  atrophied  elsewhere. 

of  inferences  based,  some  of  them,  on  actual  observation  and 
others  on  analogy,  etc. 

The  figures  will  convey  some  information,  though  appear- 
ances in  all  such  cases  must  be  interpreted  cautiously  for  the 
reasons  already  mentioned. 

During  the  first  fourteen  days  villi  appear  over  the  whole 
surface  of  the  ovum ;  about  this  fact  there  is  no  doubt.  At 
the  end  of  the  first  month  of  foetal  life,  a  complete  chorion 
has  been  formed,  owing,  it  would  seem,  to  the  growth  of  the 
allantois  (its  mesoblast  only)  beneath  the  whole  surface  of  the 
subzonal  membrane.  From  the  chorionic  surface  vascular  pro- 
cesses clothed  with  epithelium  project  like  the  plush  of  velvet. 


REPRODUCTION. 


83 


le  the  outermost 
)me  other  devel- 
ibered,  however, 
ssent  a  mixture 


The  allantois  is  compressed  and  devoid  of  a  cavity,  but  abun- 
dantly supplied  with  blood-vessels  by  the  allantoic  arteries  and 


./ . 


,t)r\ 


to  the  oTum.  at  different 
Rbadecl  tranaveraely.  In 
o).  1.  Ovum  reatine  on 
n ;  8.  Completion  of  the 
horion ;  8.  Tlie  vilU,  spe- 
id  eiMwliere. 


observation  and 


AH 


Fio.  91.-Va8cular  system  of  tlie  human  (cetus,  reprMented  diagnmmatically  (Huxley). 
H,  heart ;  TA.  aortic  trunk  ;  c,  common  carotid  artery :  c'.  external  carotid  artery ;  c", 
internal  carotid  artery ;  «,  subclavian  i^tery ;  v,  vertebral  arterv ;  1.  8.  3.  4,  5,  aortic 
arches ;  A',  dorsal  aorta ;  o,  omphalo-mesenteric  artery ;  d».  vitelline  duct ;  o\  omphalo- 
mesenteric vein ;  V',  unibiUcal  vesicle ;  tip,  portal  vein ;  L,  liver ;  u,  u,  umbiUcal  arteries ; 
u",  u",  their  endings  in  the  placenta ;  u',  umbiUcal  vein ;  Dii,  ductus  venosus ;  vA,  hepaUc 
vein ;  ev,  inferior  vena  cava ;  tii{,  iliac  veins ;  <m,  vena  acygoa ;  vc',  posterior  cardinal 
vein ;  DC,  duct  of  Cuvier ;  P,  lung. 

veins,  which  of  course  terminate  in  capillaries  in  the  villi. 
Compare  the  whole  series  of  figures. 


though  appear- 
Autiously  for  the 

over  the  whole 
s  no  doubt.  At 
omplete  chorion 
e  growth  of  the 
)le  surface  of  the 
ice  vascular  pro- 
plush  of  velvet. 


Fia.  83.— Human  ova  during  earlv  stages  of  development.  A  and  B,  front  and  side  view  of  an 
ovum  supposed  to  he  about  thirteen  days  old ;  e,  emhiyonic  area  (Quain,  after  Beichert) ; 
0,  ovum  of  four  to  live  weeks,  showing  the  general  structureof  the  ovtmi  before  formation 
of  the  placenta.  Part  of  the  wall  of  the  ovum  is  removed  to  show  the  embryo  in  position 
(after  AUsn  Thomson). 

At  this  stage  the  condition  of  the  chorion  suggests  the  type 
of  the  diffuse  placenta  which  is  normal  for  certain  groups  of 
animals,  as  will  presently  be  learned. 

The  subsequent  changes  are  much  better  understood,  for 


u 


ANIMAL  PHYSIOLOGY. 


parts  are  iu  general  no  longer  microscopic  but  of  considerable 
size,  and  their  real  structure  less  readily  obscured  or  obliterated. 
The  amniotic  cavity  continues  to  enlarge  by  growth  of  the 
walls  of  the  amnion  and  is  kept  filled  with  a  fluid ;  the  yelk-sac 
is  now  very  small ;  the  decidua  reflexa  becomes  almost  non- 
vascular, and  fuses  finally  with  the  decidua  vera  and  the  cho- 
rion, which  except  at  one  part  has  ceased  to  be  villous  and  vas- 
cular ;  so  that  becoming  thinner  and  thinner  with  the  advance 
of  pregnancy,  the  single  membrane,  arising  practically  from 
this  fusion  of  several,  is  of  a  low  type  of  structure,  the  result  of 


Fio.  8S.— Human  embryo,  twelve  weeln  old,  with  Km  ooverinn ;  natiml  aiae.  The  lutTelHXtrd 
pnimm  from  the  naTel  to  the  placenta,  b,  amnion ;  c,  chorion  ;  d,  placenta ;  d',  remains 
of  tufts  on  the  smooth  chorion ;  /,  decidua  rt/Uxa  (inner) ;  g,  decidua  vera  (outer).  (Haec- 
kel  after  Bemhard  8cl)iiltse.) 

gradual  degeneration,  as  the  rdle  they  once  played  was  taken 
up  by  other  parts. 

But  of  paramount  importance  is  the  formation  of  the  pla- 
centa. The  chorion  ceases  to  be  vascular  except  at  the  spot  at 
which  the  villi  not  only  remain,  but  become  more  vascular  and 
branch  into  arborescent  forms  of  considerable  complexity.  It 
is  discoidal  in  form,  made  up  of  a  foetal  part  just  described  and 


-a.^ 


REPRODUCTION. 


86 


of  considerable 
sd  or  obliterated, 
r  growth  of  the 
id;  the  yelk-sac 
les  almost  non- 
ra  and  the  cho- 
villous  and  vas- 
ith  the  advance 
jractically  from 
ire,  the  result  of 


a  maternal  part,  the  decidua  serotina,  the  two  becoming  blended 
so  that  the  removal  of  one  involves  that  of  more  or  less  of  the 
others.  The  connection  of  parts  is  far  closer  than  that  described 
for  the  rabbit ;  and,  even  with  the  preparation  that  Nature  makes 
for  the  final  separation  of  the  placenta  from  both  foetus  and 


vJ. 


■y 


f 


ktt.Vv 


ral  liae.  The  nuTelHXtrd 
d,  pUtoenta ;  d',  remains 
ilia  vera  (oatw).   (Haec- 


layed  was  taken 

ition  of  the  |jla- 
pt  at  the  spot  at 
Lore  vascular  and 
I  complexity.  It 
list  described  and 


Fio.  94.— DUurram  Oluatratlng  the  decidua,  placenta,  etc.  (after  LiAKeols).  e,  embryo ; 
i.  Intestine  ;  p,  pedicle  of  the  umbilical  vetiicle  :  ti.  v,  umbilical  vesicle ;  a,  amnion  ;  eft, 
chorion:  v.  t,  vascular  tufia  of  the  chorion,  constituting  the  foetal  portion  of  the  placenta; 
m.  p,  maternal  portion  of  the  placenta ;  d.  v,  decidua  vera ;  d.  r.  decidua  reitoxa ;  al, 
lUiantoia. 

mother,  this  event  does  not  take  place  without  soma  rupture  of 
vessels  and  consequent  haemorrhage. 

It  is  difficult  to  conceive  of  the  great  vascularity  of  the 
human  placenta  without  an  actual  examination  of  this  structure 
itself,  \Aiich  can  be  done  after  being  cast  off  to  great  advan- 
tage when  floating  in  water ;  by  which  simple  method  also  the 
thinness  and  other  characteristics  of  the  membranes  can  be 
well  made  out. 

The  great  vessels  conveying  the  foetal  blood  to  and  from  the 
placenta  are  reduced  to  three,  two  arteries  and  one  vein.  The 
villi  of  the  placenta  (chorion)  are  usually  said  to  hang  freely 


illj^gjl^.',;  .  ■   ' 


T 


p. 


86 


ANIMAL  PHYSIOLOGY. 


in  the  blood  of  the  large  irregular  sinuses  of  the  decidua  sero- 
tina;  but  this  is  so  unlike  what  prevails  in  other  groups  of 
animals  that  we  can  not  refrain  from  believing  that  the  state- 
ment is  not  wholly  true. 

The  Zonary  Fhwenta.— In  this  type  the  placenta  is  formed 
along  abroad  equatorial  belt, leaving  the  poles  free.  This  form 
of  placentation  is  exemplified  in  the  carnivora,  hyrax,  the  ele- 
phant, etc. 

In  the  dog,  for  example,  the  yelk-sac  is  large,  vascular,  does 
not  fuse  with  the  chorion,  and  persists  throughout.  A  rudiment- 
ary discoid  placenta  is  first  formed,  as  in  the  rabbit ;  this  grad- 
ually spreads  over  the  whole  central  area,  till  only  the  extremes 
(poles)  of  the  ovum  remain  free ;  villi  appear,  fitting  into  pits 
in  the  uterine  surface,  the  maternal  and  foetal  parts  of  the  pla- 
centa becoming  highly  vascular  and  closely  approximated. 
The  chorionic  zone  remains  wider  than  the  placental.  As  in 
man  there  is  at  birth  a  separation  of  the  maternal  as  well  as 
foetal  part  of  the  placenta-^i.  e.,  the  latter  is  deciduate ;  there  is 
also  the  beginning  of  a  decidua  reflexa. 

The  Diffiue  Placenta. — As  found  in  the  horse,  pig,  lemur,  etc., 
the  allantois  completely  incloses  the  embryo,  and  it  becomes 
villous  in  all  parts,  except  a  small  area  at  each  pole. 

The  Folycotyledonury  Flaoenta.— This  form  is  that  met  with  in 
ruminants,  in  which  case  the  allantois  completely  covers  the 
surface  of  the  subzonal  membrane,  the  placental  villi  being 
gathered  into  patches  {cotyledons),  which  are  equivalent  to  so 
many  independent  placentas.  The  component  villi  fit  into  cor- 
responding pits  in  the  uterine  wall,  which  is  specially  thickened 
at  these  points.  When  examined  in  a  fresh  condition,  under 
water,  they  constitute  very  beautiful  objects. 

Comparing  the  formation,  complete  development,  and  atro- 
phy (in  some  cases)  of  the  various  foetal  appendages  in  mam- 
mals, one  can  not  but  perceive  a  common  plan  of  structure, 
with  variations  in  the  preponderance  of  one  part  over  another 
here  and  there  throughout.  In  birds  these  structures  are  sim- 
pler, chiefly  because  less  blended  and  because  of  the  presence 
of  much  food-yelk,  albumen,  egg-shell,  etc.,  on  the  one  hand, 
and  the  absence  of  a  uterine  wall,  with  which  in  the  mammal 
the  membranes  are  brought  into  close  relationship,  on  the  other ; 
but,  as  will  be  shown  later,  whatever  the  variations,  they  are 
adaptations  to  meet  common  needs  and  subserve  common  ends. 


;\ 


he  decidua  sero- 
other  groups  of 
^  that  the  state- 

centa  is  formed 
free.  This  form 
I,  hyrax,  the  ele- 

e,  vascular,  does 
at.  A  rudiment- 
i,bbit ;  this  grad- 
nly  the  extremes 
fitting  into  pits 
parts  of  the  pla- 
''  approximated, 
laceutal.  As  in 
emal  as  well  as 
ciduate ;  there  is 

pig,  lemur,  etc., 
and  it  becomes 
pole. 

that  met  with  in 
etely  covers  the 
>ntal  villi  being 
equivalent  to  so 
villi  fit  into  cor- 
jcially  thickened 
condition,  under 

}ment,  and  atro- 
adages  in  mam- 
an  of  structure, 
irt  over  another 
uctures  are  sim- 
I  of  the  presence 
n  the  oile  hand, 
in  the  mammal 
lip,  on  the  other ; 
'iations,  they  are 
76  common  ends. 


88 


ANIMAL  PHYSIOLOGY. 


tissue,  in  which  capillaries  abound,  are  covered  with  a  flat  epi- 
thelium; the  maternal  crypts  correspond,  being  composed  of 
a  similar  matrix,  lined  with  epithelium  and  permeated  by 
capillary  vessels,  which  constitute  a  plexus  or  mesh-work.  It 
thus  results  that  two  layers  of  epithelium  intervene  between 
the  maternal  and  f  cetal  capillaries. 

The  arrangement  is  substantially  the  same  in  the  diffuse  and 
the  cotyledonary  placenta. 

In  the  deciduate  placenta,  naturally,  there  is  greater  compli- 
cation. 

In  certain  forms,  as  in  the  fox  and  cat,  the  maternal  tis- 
sue shows  a  system  of  trabeculee  assuming  a  mesied  form, 
in  which  run  dilated  capillaries.  These,  which  are  'overed 
with  a  somewhat  columnar  epithelium,  are  every wh  re  in 
contact  with  the  foetal  villi,  which  are  themselves  covered  with 
a  flat  epithelium. 


tF^ 


Fio.  100. 


Fio.  101. 


Fto  100.— Placenta  of  a  sloth.  Flat  maternal  epithelial  cells  ibown  In  poaitlon  on  right  side ; 
on  left  they  are  removed  and  dilated ;  maternal  veaael  with  its  blood-corpuacteB  ezpoaed. 

Fh>.  101.— Structure  of  human  plaoenta ;  da,  decidua  aerotina :  (,  trabecubB  of  aerotina  paMiiw 
to  foetal  villi ;  ca,  ourling  artenr ;  vp,  utero-plaoental  vein ;  x,  prolongation  of  matenuu 
'  tiarae  on  eztnior  of  villua,  outside  cellular  layer  e',  which  may  represent  either  endothe- 
lium of  maternal  blood-vessels  or  delicate  connective  tissue  of  the  serotina  or  both ;  e'  ma- 
ternal cells  of  the  serotina. 

In  the  case  of  the  sloth,  with  a  more  discoidal  placenta,  the 
dilatation  of  capillaries  and  the  modification  of  epithelium 
are  greater. 

In  the  placenta  of  the  apes  and  of  the  human  subject  the 
most  marked  departure  from  simplicity  is  found.    The  maternal 


1 


1  with  a  flat  epi- 
ng  composed  of 
I  permeated  by 
mesh- work.  It 
tervene  between 

a  the  diffuse  and 

greater  compli- 

le  maternal  tis- 
tt  mesied  form, 
ch  are  'overed 
every wh  re  in 
es  covered  with 


poaiti 
i-con 


itlonoD  right  iMe; 
l:C0nMi8clea  expowd. 
lUeof  aerotiiia  paaiiiMr 
longmUon  of  matonuil 
iretwnt  either  endothe- 
^roUna  or  both ;  t'  m*- 


il  placenta,  the 
of  epithelium 

an  subject  the 
The  maternal 


REPRODUCTION.  89 

vessels  are  said  to  constitute  large  intercommunicating  sinuses ; 
the  villi  may  hang  freely  suspended  in  these  sinuses,  or  be 
anchored  to  their  walls  by  strands  of  tissue.  There  is  believed 
to  be  only  one  layer  of  epithelial  cells  between  the  vessels  of 
mother  and  foetus  in  the  later  stages  of  pregnancy.  This, 
while  closely  investing  the  fcBtal  vessels  (capillaries),  really 
belongs  to  the  maternal  structures.  The  significance  of  thi.s 
general  arrangement  will  be  explained  in  the  chapter  on  the 
physiological  aspects  of  the  subject. 

It  remains  to  inquire  into  the  relation  of  these  forms  to  one 
another  from  a  phylogenetic  (derivative)  point  of  view,  or  to 
trace  the  evolution  of  the  placenta. 

Srolntion. — Passing  by  the  lowest  mammals,  in  which  the 
placental  relations  are  as  yet  imjwrf ectly  understood,  it  seems 
clear  that  the  simplest  condition  is  found  in  the  rodentia. 
Thus,  in  the  rabbit,  as  has  been  described,  both  yelk-sac  and . 
allantois  take  a  nutritive  part ;  but  the  latter  remains  small. 
In  forms  above  the  rodents,  the  allantois  assumes  more  and 
more  importance,  becomes  larger,  and  sooner  or  later  predomi- 
nates over  the  yelk-sac. 

The  discoidal,  zonary,  cotyledonary,  etc.,  are  plainly  evolu- 
tions from  the  diffuse,  for  both  differentiation  of  structure  and 
integration  of  parts  are  evident.  The  human  placenta  seems 
to  have  arisen  from  t*"J  diffuse  form ;  and  it  will  be  remem- 
bered that  it  is  at  one  period  represented  by  the  chorion  with 
its  villi  distributed  universally. 

The  resemblance  in  the  embryonic  membranes  at  any  early 
stage  in  man  and  other  mammals  to  those  of  birds  certainly 
suggests  an  evolution  of  some  kind,  though  exactly  along  what 
lines  that  has  taken  place  it  is  diflScult  to  determine  with  exact- 
ness ;  however,  as  before  remarked,  nearly  all  the  complications 
of  the  higher  forms  arise  by  concentration  and  fusion,  on  the  one 
hand,  and  atrophy  and  disappearance  of  parts  once  functionally 
active,  on  the  other. 

Smnmary. — The  ovum  is  a  typical  cell ;  unspecialized  in  most 
directions,  but  so  specialized  as  to  evolve  from  itself  compli- 
cated structures  of  higher  character.  The  segmentation  of  the 
ovum  is  usually  preceded  by  fertilization,  or  the  union  of  the 
nuclei  of  male  and  female  cells,  which  is  again  preceded  by  the 
extrusion  of  polar  globules.  In  the  early  changes  of  the  ovum, 
including  segmentation,  periods  of  rest  and  activity  alternate. 
The  method  of  segmentation  has  relation  to  the  quantity  and 
arrangement  of  the  food-yelk.     Ova  are  divisible  generally 


90 


ANIMAL  PHYSIOLOGY. 


into  completely  segmenting  (holoblastic),  and  those  that  under- 
go segmentation  of  only  a  part  of  their  substance  (meroblastic) ; 
but  the  processes  are  fundamentally  the  same. 

Provision  is  made  for  the  nutrition,  etc.,  of  the  ovum,  when 
fertilized  (oosperm)  by  the  formation  of  yelk-sac  and  allan- 
tois;  as  development  proceeds,  one  becomes  more  promiiient 
than  the  other.  The  allantois  may  fuse  with  adjacent  mem- 
branes and  form  at  one  part  a  condensed  and  hypertrophied 
chorion  (placenta),  with  corresponding  atrophy  elsewhere.  The 
arrangement  of  the  placenta  varies  in  different  groups  of  ani- 
mals so  constantly  as  to  furnish  a  basis  for  classification.  What- 
ever the  variations  in  the  structure  of  the  placenta,  it  is  always 
highly  vascular ;  its  parts  consist  of  villi  fitting  into  crypts  in 
the  maternal  uterine  membrane—both  the  villi  and  the  crypts 
being  provided  with  capillaries  supported  by  a  connective-tissue 
matrix  covered  externally  by  epithelium.  The  placenta  in  its 
different  forms  would  appear  to  have  been  evolved  from  the 
diffuse  type. 

The  peculiarities  of  the  embryonic  membranes  in  birds  are 
owing  to  the  presence  of  a  large  food-yelk,  egg-shell,  and  egg- 
membranes  ;  but  throughout,  vertebrates  follow  in  a  common 
line  of  development,  the  differences  which  separate  them  into 
smaller  and  smaller  groups  appearing  later  and  later.  The 
same  may  be  said  of  the  animal  kingdom  as  a  whole.  This 
seems  to  point  clearly  to  a  common  origin  with  gradual  diver- 
gence of  type. 


THE  DEVELOPMENT  OF  THE  EMBRYO  ITSELF. 

We  now  turn  to  the  development  of  the  body  of  the  animal 
for  which  the  structures  we  have  been  describing  exist.  It  is 
important,  however,  to  remember  that  the  development  of  parts, 
though  treated  separately  for  the  sake  of  convenience,  really 
goes  on  together  to  a  certain  extent;  that  new  structures  do  not 
appear  suddenly  but  gradually ;  and  that  the  same  law  applies 
to  the  disappearance  of  organs  which  are  being  superseded  by 
others.  To  represent  this  completely  would  require  lengthy  de- 
scriptions and  an  unlimited  number  of  cuts ;  but  with  the  above 
caution  it  is  hoped  the  student  may  be  able  to  avoid  erroneous 
conceptions,  and  form  in  his  own  mind  that  series  of  pictures 
which  can  not  be  well  furnished  in  at  least  the  space  we  have 
to  devote  to  the  subject.    But,  better  than  any  abstract  state- 


lIlijIllyilpjiMLM, 


hose  that  under- 
go (meroblastic) ; 

the  ovum,  when 
k-sac  and  allan- 
more  promiiient 
adjacent  mein- 
d  hypertrophied 
elsewhere.  The 
t  groups  of  ani- 
ification.  What- 
mta,  it  is  always 
ig  into  crypts  in 
i  and  the  crypts 
ionnective-tissue 
e  placenta  in  its 
rolved  from  the 

mes  in  birds  are 
^-shell,  and  egg- 
>w  in  a  common 
[)arate  them  into 
and  later.  The 
a  whole.  This 
1  gradual  diver- 


3  ITSELF. 

ly  of  the  animal 
ting  exist.  It  is 
opment  of  parts, 
avenience,  really 
structures  do  not 
»me  law  applies 
^  superseded  by 
|uire  lengthy  de- 
t  with  the  above 
avoid  erroneous 
jries  of  pictures 
e  space  we  have 
y  abstract  state- 


THE  DEVELOPMENT  OP  THE  EMBRYO  ITSELF.  91 

ments  or  pictorial  representations,  would  be  the  examination  of 
a  setting  of  eggs  day  by  day  during  their  development  under  a 


®  a  ® 

8  f 


11 


^    " 


Via.  l(N.-Varioua  lUgM  In  the  derelopmeiit  of  the  frog  from  Uwent  (after  Howm).  1.  TIm 
Betrmentlng  oTum,  ahowiiifr  flnt  dearage  farrow.  S.  Section  of  the  above  Mrignt  angles 
to  the  furrow.  8.  Same,  on  amwaranoe  of  aecond  furrow,  Tiewed  •liRhthr  from  aboye. 
4.  The  latter  aeen  from  beneatL  6.  The  lame,  on  aimearance  of  flnt  homontaifurrow. 
8.  The  same,  wen  from  above.  7.  Longitudinal  wcnon  of  «.  8  and  0.  Two  lAaaes  In 
segmentation,  on  appearance  of  fourth  and  ilfth  furrows.  10.  Longitudinal  Tertical  section 
at  a  slightly  later  stage  than  the  above.  U.  Later  stage.  Unpm- idgnMnted  pc^  dividing 
morarapWr  than  lower  IS.  Later  phase  of  11.  isTXonglfiidlnal  vertical  sectitni  of  18. 
14.  SecmentinK  ovum  at  blastopore  stage.  16.  Longitud&ial  vertical  section  of  same. 
IS  wl  15  K  la  (all  others  »  B).  16.  Longitudinal  vertical  section  of  embijo  at  a  stage 
teter  than  14  (1  x  10).  ne,  nucleus ;  c.  c,  cleavage  cavity  ;  epi  ^Whta*.!  fj<  yeUt-hejS'* 
lower-layer  cells ;  M,  blastopore ;  at,  archenteron  (mid-gut) :  hb,  hypoblast ;  dm,  undiffer- 
entiated mesoblast ;  Ot,  notochord ;  n.  a,  neural  (cerebro-qmial)  axis. 

hen.  This  is  a  very  simple  matter,  and,  while  the  making  and 
mounting  of  sections  from  hardened  specimens  is  valuable,  it 
may  require  more  time  than  the  student  can  spare ;  but  it  is 
neither  so  valuable  nor  so  easily  accomplished  as  what  we  have 
indicated ;  for,  while  the  lack  of  sections  made  by  the  student 


liawiBMiWtt 


mam 


fsismm 


02 


ANIMAL  PHYSIOLOGY. 


may  be  made  up  in  ■pari  by  the  exhibition  to  him  of  a  set  of 
specimens  permanently  mounted  or  even  by  plates,  nothing  can, 
in  our  opinion,  take  the  place  of  the  examination  of  eggs  as  we 
have  sUf  nrested.  It  prepares  for  the  study  of  the  development 
of  the  mammal,  and  exhibits  the  membranes  in  a  simplicity, 
freshness,  and  beauty  which  impart  a  knowledge  that  only 
such  direct  contact  with  nature  can  supply.  To  proceed  with 
great  simplicity  and  very  little  apparatus,  one  requires  but  a 
forceps,  a  glass  dish  or  two,  a  couple  of  watch-glasses,  or  a 
broad  section-lifter  (even  a  case-knife  will  answer),  some  water, 
containing  just  enough  salt  to  be  tasted,  rendered  lukewarm 
(blood-heat). 

Holding  the  egg  longitudinally,  crack  it  across  the  center 
transversely,  gently  and  carefully  pick  away  the  shell  and  its 
membranes,  when  the  blastoderm  may  be  seen  floating  upward, 
as  it  always  does.  It  should  be  well  examined  in  position, 
using  a  hand  lens,  though  this  is  not  essential  to  getting  a  fair 
knowledge ;  in  fact,  if  the  examination  goes  no  further  than 
the  naked-eye  appearances  of  a  dozen  eggs,  selecting  one  every 
twenty-four  hours  during  incubation,  when  opened  and  the 
shell  and  membranes  well  cleared  away,  such  a  knowledge  will 
be  supplied  as  can  be  obtained  from  no  books  or  lectures  how- 
ever good.  It  will  be,  of  course,  understood  that  the  student 
approaches  these  examinations  with  some  ideas  gained  from 
plates  and  previous  reading.  The  latter  will  furnish  a  sort  of 
biological  pabulum  on  which  he  may  feed  till  he  can  furnish 
for  himself  a  more  natural  and  therefore  more  healthful  one. 
While  these  remarks  apply  with  a  certain  degree  of  force  to  all 
the  departments  of  physiology,  they  are  of  special  importance 
to  aid  the  constructive  faculty  in  building  up  correct  notions 
of  the  successive  rapid  transformations  that  occur  in  the  de- 
velopment of  a  bird  or  mammal. 

Fig.  103  shows  the  embryo  of  the  bird  at  a  very  early 
period,  when  already,  however,  some  of  the  main  outlines  of 
structure  are  marked  out.  Development  in  the  fowl  is  so  rapid 
that  a  few  days  suffice  to  outline  all  the  principal  organs  of 
the  body.  In  the  mammal  the  process  is  slower,  but  in  the 
main  takes  place  in  the  same  fashion. 

As  the  result  of  long  and  patient  observation,  it  is  now  set- 
tled that  all  the  parts  of  the  most  complicated  organism  arise 
from  the  three-layered  blastoderm  previously  figured ;  every 
part  may  be  traced  back  as  arising  in  one  or  other  of  these  lay- 
ers of  cells — the  epiblast,  mesoblast,  or  hypoblast.   It  frequently 


him  of  a  set  of 

ates,  nothing  can, 

ion  of  eggs  as  we 

the  development 

in  a  simplicity, 
rledge  that  only 
To  proceed  with 
le  requires  but  a 
itch-glasses,  or  a 
wer),  some  water, 
idered  lukewarm 

across  the  center 

the  shell  and  its 

floating  upward, 

ined  in  position, 

I  to  getting  a  fair 
no  further  than 

lecting  one  every 
opened  and  the 
a  knowledge  will 
J  or  lectures  how- 
that  the  student 
leas  gained  from 
furnish  a  sort  of 

II  he  can  furnish 
ore  healthful  one. 
ree  of  force  to  all 
lecial  importance 
p  correct  notions 
occur  in  the  de- 

at  a  very  early 
main  outlines  of 
6  fowl  is  so  rapid 
incipal  organs  of 
lower,  but  in  the 

on,  it  is  now  set- 
1  organism  arise 
y  figured ;  every 
ther  of  these  lay- 
kst.    It  frequently 


THE  DEVELOPMENT  OP  THE  EMBRYO  ITSELF. 


93 


AS'jfZ 


happens  that  an  organ  is  made  up  of  cells  derived  from  more 
than  one  layer.  Structures  may,  accordingly,  be  classified  as 
epiblastic,  mesoblastic,  or  hypoblas- 
tic;  for,  when  two  strata  of  cells 
unite  in  the  formation  of  any  part, 
one  is  always  of  subordinate  impor- 
tance to  the  other :  thus  the  digestive 
organs  are  made  up  of  mesoblast  as 
well  as  hypoblast,  but  the  latter 
constitutes  the  essential  secreting 
cell  mechanism.  As  already  indi- 
cated, the  embryonic  membranes 
are  also  derived  from  the  same 
source. 

The  epihlast  gives  rise  to  the  skin 
and  its  appendages  (hair,  nails,  feath- 
ers, etc.),  the  whole  of  the  nervous 
system,  and  the  chief  parts  of  the  or- 
gans of  special  sense. 

The  meaoblaat  originates  the  skel- 
eton, all  forms  of  connective  tissue, 
including  the  framework  of  glands, 
the  muscles,  an<i  the  epithelial  (en- 
dothelial) structures  covering  serous 
membranes. 

The  hypoblast  furnishes  the  se- 
creting cells  of  the  digestive  tract 
and  its  appendages— as  the  liver  and 
pancreas— the  lining  epithelium  of 
the  lungs,  and  the  cells  of  the  secret- 
ing mucous  membranes  of  their 
framework  of  bronchial  tubes. 

It  is  difficult  to  overrate  the  im- 
portance of  these  morphological  gen- 
eralizations for  the  physiologist ;  for, 
once  the  origin  of  an  organ  is  known, 
its  function  and  physiological  rela- 
tions generally  may  be  predicted  with 
considerable  certainty.  We  shall  en- 
deavor to  make  this  prominent  in  the  future  chapters  of  this 

work. 

Being  prepared  with  these  generalizations,  we  continue  our 
study  of  the  development  of  the  bird's  embryo.    Before  the  end 


Flo.  MM.— Embryo  fowl  8  mm.  long, 
of  about  twenty-four  hours,  leen 
from  above.  i*K.  (Haddon. 
after  KnUiker.)  Mn,  ubIod  of 
the  medullary  folds  in  the  reston 
of  the  hind-brain ;  Pr.  primftiTe 
streak  ;  Pk,  parieUl  map ;  Bf, 
posterior  portion  of  widely-open 
neuna  groove ;  R/',  anterior  part 
of  neural  groove ;  Bw,  nmrat 
rWlge ;-«(«,  trunk-sone ;  vAf,  an- 
twlor  amniotic  told ;  «0,  anterior 
umbilioal  sinus  showing  through 
the  blastoderm.  His  divides  the 
embryonio  rudiment  int<>  a  oen- 
tral  trunk-sone,  and  a  pah*  of 
lateral  or  parietal  sones. 


iMi 


HM 


gMttu'!-;.-- 


94 


ANIMAL  PHYSIOLOGY. 


of  the  first  twenty-four  hours  such  an  appeamnce  as  that  repre- 
sented in  Fig.  104  is  presented. 

Htf" 


B     \ 


^"^  i?*!."*?"^*??"®  Mctlon  through  the  mediillanr  groove  and  half  the  blaatodmn  of  a 

chick  of  eighteen  hours  (Foster  and  Balfour).    E,e~"-'—^-  " •-* — ■    "- — -•    - 

m/,  medullary  fold ;  mg.  medullary  grooye ;  ck,  i 


ibiart ;  M,  meaoblaM ;  H,  hypoblaM : 


The  mounds  of  cells  forming  the  medullary  folds  are  seen 
coming  in  contact  to  form  the  medvXlary  {neural)  canal. 


'^"k?*:"^!*?^*']??  ■«*'»'»  o'  fwjMfyo  chick  at  end  of  flrrt  day  (after  KOlliker).  Jf,  meao- 
SSniL^'  ^f^^  Lr''i°^V?'*^P'^ '  *  eplblai* :  mg,  medullary  groove ;  mf,  me- 
dullary fold ;  ch,  chorda  dorwiis ;  P,  protovertebral  plate ;  dm,  division  of  meaobUwi. 

The  notochord,  marking  out  the  future  bony  axis  of  the 
body,  may  also  be  seen  during  the  first  day  as  a  well-marked 
linear  extension,  just  beneath  the  medullary  groove.    The  clear- 


Fio.  108.-TransvM«e  iMtlpn  of  chick  at  end  of  second  day  (KOlliker).  E,  eptblaat :  H.  hypo- 
blast ;  «.  m,  external  plate  of  mewiblast  dividing  (cleavage  of  mesoblaat)Ttii./,  medullMT 
Md  ;  m.  g,  medullary  groove ;  ao,  aorU  ;  p,  pteuroperttoneal  cavity ;  P,  prutovertebnU 

age  of  the  mesoblast,  resulting  in  the  commencement  of  the 
formation  of  aoinalojdeure  (body-fold)  and  the  aplanchnopleure 
(visceral  fold),  is  also  an  early  and  important  event.  These  give 
rise  between  them  to  the  pleuro-perUoneal  cavity.  The  portions 
of  mesoblast  nearest  the  neural  canal  form  masses  {vertebral 
platea)  distinct  from  the  thinner  outer   ones  {ItUetal  platea). 


THE  DEVELOPMENT  OP  THE  EMBRYO  ITSELF. 


95 


ce  as  that  repre- 


mg 


tif  the  blMtodmn  of  a 
noblMt ;  U,  IqrpoblMt : 


y  folds  are  seen 
al)  canal. 


terKOlliker).  Jf,  meao- 
itlUuy  groove ;  m/,  me- 
iTiaion  of  meaoblaat. 


>ny  axis  of  the 
8  a  well-marked 
Qve.    The  cleav- 


e.m. 


K,  epibUMt ;  H.  taw- 
bbMt)  \m.f,  medullary 
vitjr ;  P,  pnkovertebnU 


ncement  of  the 
ipianchnopleure 
ent.  These  give 
'.  The  portions 
lasses  {vertebral 
{lateral  pkUes). 


— f-a.p. 


The  vertebral  plates,  when  distinctly  marked  off,  as  repre- 
sented in  the  figure,  are  termed  the  protovertebrcB  {mesoblastic 
somites),  and  represent  the  future  vertebra  and  the  voluntary 
muscles  of  the  trunk ;  the  former  arising  from  the  inner  sub- 
divisions, and  the  latter  from 
the  outer  {musde-plates).  It 
will  be  understood  that  the  pro- 
tovertebrffi  are  the  results  of 
transverse  division  of  the  col- 
umns of  mesoblast  that  formed 
the  vertebral  plates. 

Before  the  permanent  verte- 
brsB  are  formed,  a  reunion  of 
the  original  protovertebrse  takes 
place  as  one  cartilaginous  pillar, 
followed  by  a  new  segmentation 
midway  between  the  original 
divisions. 

It  thus  appears  that  a  large 
number  of  structures  either  ap- 
pear or  are  clearly  outlined  dur- 
ing the  first  day  of  incubation : 
the  primitive  streak,  primitive 
groove,  medullary  plates  and 
groove,  the  neural  canal,  the 
head-fold,  the  cleavage  of  the 
mesoblast,  the  protovertebree, 
with  traces  of  the  amnion  and 


Fio.  lOr.— Bmbnro  of  ohiok,  between  thirty 
•nd  thlrty-a»  houn,  viewed  from  above 
•8  an  opaque  object  (Faster  and  Balfour). 


/.  b.  foiebrain  ;'  m.  b,  midbrain  ;  h.  b, 
niiul-brain 


pit; 


optic  veaicle ;  au.  p, 
vitelline  vein;  />.  v, 
t  f u 


auditory  pi 
meaoblMtio  loi 
tton  of  mediillary 


fold ;  p.r,  remains  of  primitive  groove ; 
a.  p,  area  pellucida. 


lie  :  lit.  /,  line  of 

■  folds  above  medullary 

oftnai ;  t.  r,  alnus  rhomboidalis ;  (,  tail- 


area  opaca. 

During  the  second  day  near- 
ly all  the  remaining  important 
structures  of  the  chick  are 
marked  out,  while  those  that 

arose  during  the  first  day  have  progressed.  Thus,  the  medullary 
folds  close ;  there  is  an  increase  in  the  number  of  protoverte- 
bree ;  the  formation  of  a  tubular  heart  and  the  great  blood-ves- 
sels ;  the  appearance  of  the  Wolffian  duct ;  the  progress  of  the 
head  region ;  the  appearance  of  the  three  cerebral  vesicles  at 
the  anterior  extremity  of  the  neural  canal ;  the  subdivision  of 
the  first  cerebral  vesicle  into  the  optic  vesicles  and  the  begin- 
nings of  the  cerebrum ;  the  auditory  pit  arising  in  the  third 
cerebral  vesicle  (hind-brain) ;  cranial  flexure  commences;  both 
head  and  tail  folds  become  more  distinct ;  the  heart  is  not  only 


••  .UJ,WWW(lMI(.i>.. 


96 


ANIMAL  PHYSIOLOGY. 


formed,  but  its  curvature  becomes  more  marked  and  rudiments 
of  auricles  arise ;  while  outside  the  embryo  itself  the  circula- 
tion of  the  yelk-sac  is  established,  the  allantois  originates,  and 
the  amnion  makes  rapid  progress. 

It  may  be  noticed  that  the  cerebral  vesicles,  the  optic  vesi- 
cles, and  the  auditory  pit  are  all  derived  from  the  epiblastic 
accumulations  which  occur  in  the  anterior  extremity  of  the 
embryo ;  and  their  early  appearance  is  prophetic  of  their  physi- 
ological importance. 

The  heart,  too,  so  essential  for  the  nutrition  of  the  embryo, 
by  distributing  a  constant  blood-stream,  is  early  formed,  and 


Fta.  108.— Dlumn  reprMentiiig  under  Mrfaoe  of  an  embryo  rabUt  of  nine  dajTH  wid  three 

t  deTelopmmit  of  the  bewt  (after  Allen  Thomwn).    A,  view  of  the 

entire  embryo ;  B,  an  enlarged  outline  of  the  heart  of  A ;  0,  later  itage  of  thedoTelopment 


houn  old,  Uluatrating  derel 

entire  embryo ;  B,  an  enlarg 

of  B ;  A  ft,  ununited  heart ;  o  a,  aorta ;  tw,  ▼tteillne  Teina. 


becomes  functionally  active.  It  arises  beneath  the  hind-end  of 
the  fore-gut,  at  the  point  of  divergence  of  the  folds  of  the 
splanchnopleure,  and  so  lies  within  the  pleuro-peritoneal  cav- 
ity, and  is  derived  from  the  mesoblast.  At  the  beginning  the 
heart  consists  of  two  solid  columns  ununited  in  front  at  first ; 
later,  these  fuse,  in  part,  so  that  they  have  been  compared  with 
an  inverted  Y,  in  which  the  heart  itself  would  correspond  to  the 
lower  stem  of  the  letter  (a)  and  the  great  veins  (vitelline)  to  its 
main  limbs.  The  solid  cords  of  mesoblast  become  hollow  prior 
to  their  coalescence,  when  the  two  tubes  become  one. 


^  >MUM«i#i(biN4«M«i^iirftK^' 


■*iiw»,«iw)»WM»i  »,k  fiimim 


THE  DEVELOPMENT  OF  THE  EMBRYO  ITSELF. 


97 


)d  and  rudiments 
tself  the  circula- 
Ls  originates,  and 

a,  the  optic  vesi- 
m  the  epiblastic 
jxtremity  of  the 
ic  of  their  physi- 

in  of  the  embryo, 
irly  formed,  and 


i    -* 


it  at  nine  dajrw  wid  three 
lionieaii).  Al  view  ot  the 
■tage  of  the  development 


h  the  hind-end  of 
the  folds  of  the 
o-peritoneal  cav- 
;he  beginning  the 
L  in  front  at  first ; 
tn  compared  with 
correspond  to  the 
B  (vitelline)  to  its 
ome  hollow  prior 
le  one. 


The  entire  blood-vascular  system  originates  in  themesoblast 
of  the  area  opaca  especially ;  at  first  appearing  in  isolated  spots 
which  come  together  as  actual  vessels  are  formed.  The  student 
who  will  pursue  the  plan  of  examining  a  series  of  incubating 
eggs  will  be  struck  with  the  early  rise  and  raoid  progress  of  the 


Fia.  10B.-€!blck  on  third  day,  nen  fMm  beneath  aa  a  transparent  object,  the  head  betag 
turned  to  one  aide  (Foater  and  Balfour),  o',  falM  Monion ;  Ov*'?^52Ji£.  Vi^ShS 
hemiqdiere;  FB,  MB,  HB,  anterior,  middle,  and  pMterJor  <»w>»^ '^^^^.S^.^Pg? 
veBloleTot,  auditory  veaiole ;  o/v,  omphalo-meaenteric  velna ;  fl»^oart ;  Ao,  buIlniB  artej 
rionis :  «*.  notodiord ;  Ofit,  omphalo-meaenterlo  arteriea ;  Pv,  notovwtobrB ;  x,  point  of 
divergence  of  the  aplanobnopleural  folds ;  v,  termination  of  the  foregut,  v. 

vascular  system  of  the  embryo,  which  takes,  when  complete, 
such  a  form  as  is  represented  diagramatically  in  Fig.  113. 

The  blood  and  the  blood-vessels  arise  simultaneously  from 
the  cells  of  the  mesoblast  by  outgrowths  of  nuclear  prolifera- 
tion, and  in  the  case  of  vessels  (Fig.  147)  extension  of  processes, 
fusion,  and  excavation. 

The  fore-giU  is  formed  by  the  union  of  the  folds  of  the 
splanchnopleure  from  before  backward,  and  the  hind-gut  in  a 
similar  manner  by  fusion  from  behind  forward. 
7 


g 


^ 


i 
I 


fjfmivimj-LmnstglKKKHi 


am  ■a  \'rxLtu  »AHM,i»mUll 


98 


ANIMAL  PHYSIOLOGY. 


The  excretory  system  is  also  foreshadowed  at  an  early  pe- 
riod by  the  Wolffian  duct  (Fig.  114),  a  mass  of  mesoblast  cells 
near  which  the  cleavage  of  the  mesoblast  takes  place. 


During  the  latter  part  of  the  second  day  the  vascular  system, 
including  the  heart,  makes  great  progress.    The  latter,  in  con- 


Fio.  lll.-DI»gwm»nM«o  ontUnM  of  the  ew^arterUtl  ayrt^  of  *>»  ««^J!?  JS«f5?«hi!S 
bryo  Wter  AUen  Thomaon).  A.  At  a  period  cprreroondtag  to  the  UUrty-jteth  or  UMrg^ 
SfttOoup  oflnoubirtton:  B.  I*ter  iSge,  with  two  wOrt  of  •w^"?*"}-  *i  ^"2? 
M^rionu  of  he»rt ;  v,  TltelUne  arterietiTT-5,  the  aortJo  archea.  The  dotted  Unee  Indicate 
the  potition  of  the  future  arohea. 

sequence  of  excessive  growth  and  the  alteration  of  the  relative 
position  of  other  parts,  becomes  bent  up  on  itself,  so  that  it 


*t .. 


uiMlllllHUillHIiMiwMjWWWiMfcrftaiW 


THE  DEVELOPMENT  OP  THE  EMBRYO  ITSELF. 


99 


L  at  an  early  pe- 
l  mesoblast  cells 
I  place. 


Qualn).  A  repreMnts  an 
■ ;  it,  auricle;  8,  Tentride; 
rtertes ;  A,  united  aortae. 


>  vascular  system, 
The  latter,  in  con- 


«  mammal  vertebrate  em- 
the  thlrt7-Blxth  or  thirty- 
aordo  archee.    h,  bulbua 

,  The  dotted  llnee  indicate 


ion  of  the  relative 
L  itself,  so  that  it 


presents  a  curve  to  the  right  which  represents  the  venous  part 
and  one  to  the  left,  answering  to  the  arterial.  The  rudiments 
of  the  auricles  also  are  to  be  seen. 

The  arterial  system  is  represented  at  this  stage  by  the  ex- 
panded portion  of  the  heart  known  as  the  hvlbus  arteriosus, 
and  two  extensions  from  it,  the  aortee, 
which  uniting  above  the  alimentary 
canal,  form  a  single  ix)sterior  or  dorsal 
aorta.  From  these  great  arterial  ves- 
sels the  lesser  ones  arise,  and  by  sub- 
division constitute  that  great  mesh- 
work  represented  diagrammatically  in 
Figs.  112, 113,  from  which  the  course  of 
the  circulation  may  be  gathered.  The 
beating  of  the  heart  commences  be- 
fore the  corpuscles  have  become  nu- 
merous, and  while  the  tubular  system, 
through  which  the  blood  is  to  be 
driven,  is  still  very  incomplete. 

The  events  of  the  third  day  are  of 
the  nature  of  the  extension  of  parts 
already  marked  out  rather  than  the 
formation  of  entirely  new  ones.  The 
following  are  the  principal  changes: 
The  bending  of  the  head-end  down- 
ward (cranial  flexure) ;  the  turning  of 
the  embryo  so  that  it  lies  on  its  left 
side ;  the  completion  of  the  vitelline 
circulation ;  the  increase  in  the  curva- 
ture of  ihe  heart  and  its  complexity 
of  structure  by  divisions ;  the  appear- 
ance of  additional  aortic  arches  and 
of  the  cardinal  veins ;  the  formation 
of  four  visceral  clefts  and  five  vis- 
ceral arches;  a  series  of  progressive 
changes  in  the  organs  of  the  special 
senses,  such  as  the  formation  of  the 
lens  of  the  eye  and  a  secondary  optic 
vesicle;  the  closing  in  of  the  optic 
vesicle ;  and  the  formation  of  the  na- 
sal pits.  In  the  region  of  the  future  brain,  the  vesicles  of  the 
cerebral  hemispheres  become  distinct ;  the  hind-brain  separates 
into  cerebellum  and  medulla  oblongata ;  the  nerves,  both  cra- 


ne, lis.— Dtaftram  of  tiie  embiy- 
onlc  Taarular  aystem  nvieder- 
■heim).  a,  atrium ;  A.  A,  dor- 
Mi  aorta  ;  Ab,  branchial  ves- 
mem ;  Acd,  caudal  artery ;  AU, 
ollantoio  (bypoKaatrio)  arter- 
ies: Am^yitemao  arteries;  B, 
bulDus  arteriosus ;  c,  c,'  exter- 
nal and  internal  carotids ;  D, 
ductus  CuTleri  (precaval  veins) ; 
£,  external  iliac  arterifs;  0.  C, 
posterior  cardinal  v^n  ;  /e, 
common  iliao  arteries  ;  K.  L, 
giUolefts;  R. ^,  right  and  left 
roots  of  the  aorta  ;  8.  S'i 
branchial  coHecting  trunks  or 
Teins  ;  fib,  subclavian  artery ; 
8V,  subclavian  vein ;  S<,  sinus 
venosus;  r,  ventricle;  FC, an- 
terior cardinal  vein ;  Vm,  vitel- 
line veins. 


hM 


100 


ANIMAL  PHYSIOLOGY. 


nial  and  spinal,  bud  out  from  the  nervous  centers.  The  ali- 
mentary canal  enlarges,  a  fore-gut  and  hind-gut  being  formed, 
the  former  being  divided  into  oesophagus,  stomach,  and  duode- 


AA.l 


S.Ti 


BjnfJL 


no.  118.— DiMcrsm  of  draulation  of  yelk-wc  at  end  of  third  day  (Forter  and  BiOtborV 
Blaatoderai  seen  from  below.  Arteries  made  black.  H,  heart;  AA,  ncond,  third,  a^ 
fourth  aortic  arche^  AO,  dor^l  aorto:  L.  W.  4,  Irft  Titelline  Mtery;  «.  W  A,tMaX 
TiteUine  artery ;  8.  r,  ainna  terminalla ;  L.  Of,  left  vitelline  vein ;  B.  Of.  right  vitijlllne 
vein ;  S.  V,  Binus  venoms ;  D.  C,  ductus  Cuvteri ;  S.  Ca.  V,  superior  canUnal  or  Jugular 
vein ;  V.  Ca,  interior  cardinal  vein. 

num;  the  latter  into  the  large  intestine  and  the  cloaca.  The 
lungs  arise  from  the  alimentary  canal  in  front  of  the  stomach ; 
from  similar  diverticula  from  the  duodenum,  the  liver  and 
pancreas  originate.  Changes  in  the  protovertebrae  and  muscle- 
plates  continue,  while  the  Wolffian  bodies  are  formed  and  the 
Wolffian  duct  modified. 

Up  to  the  third  day  the  embryo  lies  mouth  downward,  but 
now  it  comes  to  lie  on  its  left  side.  See  Fig.  109  with  the  ac- 
companying description,  it  being  borne  in  mind  that  the  view  is 
from  below,  so  that  the  right  in  the  cut  is  the  left  in  the  em- 


»nters.  The  ali- 
it  being  formed, 
och,  and  duode- 


.ca.r. 


Lxf. 


r  (Foster  and  Balfbar) 

AA,  aecond,  third,  and 

artery ;  B.  Of.  A,  rteiit 

n ;  B.  Of.  Tight  yftMoe 

rtor  caMlnaror  Jugular 


the  cloaca.  The 
b  of  the  stomach ; 
1,  the  liver  and 
)br8B  and  muscle- 
formed  and  the 

h  downward,  but 
.  109  with  the  ac- 
d  that  the  view  is 
lie  left  in  the  em- 


THB  DEVELOPMENT  OP  THE  EMBRYO  ITSELF. 


101 


Fio.  114. 


fy. 


Fio.  no. 


Fio.  116. 


Fio.  I14.-Traiiaverw  Mctkm  through  lumbar  region  of  M«ntaTO  at  end  of  fourth  djv(Fofr 
ter  and  Balfour),  ne.  neural  canal ;  or,  poiterior  root  of  qxlnal  nerve  with  ganguon  , 
a.r^.SrSSSt:  r^.aiiteriorgWS^iSSmnof  'tf^'><«:ii,^-^)f^^^J^^. 
column  In  course  of  formatton ;  m.  p,  muacle-pUte ;  (*.  nptochwd ;  W.B,  Wolfflaai  ridge , 
™o;  donal^wta ;  v.  c.  a,  portirior'caKUnal  Tein :  W.  d,  WoMlan  duct  ,W.  «>,  W^SS? 
bod^.  condrtinc  of  tubules  wodMalplghian  oorpuaoles;  g.  e.  germinal  epitheliuAi ;  d,  oU- 
^tary^mS^  il#rSmSenclng  meSentery :  ^sonuftopleure ;  SP,  splanchnopleure  ; 


The 


V,  blood-Tessels ;  pp,  pleurt^perlSoneal  cavjfy. 

.  lis.— Diagram  of  portion  of  dlgesUTo  tract  oi  cnicK  on  luurui  u»jr ,«».  y""''S"  ,*~ 
bU^Unerepreson&hypoblast;  the  shaded  portion,  mesoblast;  Iff,  lung  diverticulum, 
expanding  at  bases  into  primary  lung  vesicle ;  «t,  stomach :  I,  liver ;  p,  panadas, 


expanding  at  bases  wto  pnmary  lung  veaicie ;  «,  ■wnuwu ;  i,  ii»ci  ,  »,  u>uc»c«>. 
no.  Iftk-Sead  of  chick  of  teird  day,  viewed  sidewise  as  a  transMjent  obfect  {Huxley).  la, 
cerabrS  hemispheres;  lb,  vesicle  of  third  ventricle;  n.  mid-brain  ;  111,  hiDd-brain ;  a. 
oDtlct^cle ;  o;  nasal  pit ;  6.  otic  vesicle ;  d,  infundlbulum ;  e,  pinea  body ;  h,  uotochord; 
\^lMUr^!^e;  VuTseveith  nerve;  VIU,  united  glossopharyngeal  and  pneumogastric 
nenrca.    1, 8, 8, 4, 6,  the  five  visceral  folds. 


>mmf- 


102 


ANIMAL  PHYSIOLOGY. 


bryo  itself.  Fig.  114  gives  appearances  furnished  by  a  vertical 
transverse  section.  The  relations  of  the  parts  of  the  digestive 
tract  and  the  mode  of  origin  of  the  lungs  may  be  learned  from 
Fig.  116. 


r,B. 


Fio.  IIV.— Head  of  chick  of  fourth  day,  riewed  from  below  as  an  opaaua  object  (Foater  and 
Balfour).  The  neck  is  cut  acroM  between  third  and  fourth  vtacwaTfoIda.  C.  H.  cerebral 
hemtopherea ;  F.  B,  veeiote  of  third  yentricle :  Op,  erebaU :  t^^,  ""•■p-'«"\*i'.?'!?"*""iJ!'' 
cavity  of  mouth :  S.  m,  superior  nuudUary  procev  (^  F.  1,  the  flrM  ▼iaeeral  fold  (mandibu- 
Ur  arch) ;  F.  S,  F.  •,  seocmd  and  third  Tiioeral  arches ;  ;v,  nasal  pit 

An  examination  of  the  figures  and  subjoini'd  descriptions 
must  suffice  to  convey  a  general  notion  of  the  subsequent  prog- 


Fio.  118.— BmbTTO  at  end  of  fourth  day,  seen  as  a  transparent  obJecUForter  and  BaUonr). 
CH,  cewsbMl  hemisphere ;  F.  0.  fore-brata,  mr  rericle  of  tUrd  vn^cle  (th^ju^noe^ 
ton).  wHh  pineal  gland  (PH)  proWtag ;  M.  B,  mid-brain ;  C6.  cerebeUum ; /r.  V,  fourth 
^utricle ;Tlei«;  «M  cholSajiMt;  Cm.  '^..•"jUtoiy  vejteWjjm.  ™P«%  m«">«7 
prooess ;  \F,»F,  etc.,  first,  second,  etc.,  visceral  folds ;  F,  fifth  nwre;  KiJ,  seventh  nerve: 
&.  PK,  rlossopharynfteal  nerve  Tfto,  pneumoMftric.  The  distrVbuUpn  of  Uiese  nerves  Is 
lUso i^dtoMedrreh: mtodiocd ;  Ht.lieart ;  MP, mnsdl<>-plates :  W,  whig :  H. L-htodUmb. 
The  amnion  has  been  removed.  jli,allantois  protruding  from  out  end  of  aomanosttlkSS. 


led  by  a  vertical 
lof  the  digestive 
Ibe  learned  from 


DEVELOPMENT  OP  THE  VASCULAR  SYSTEM. 


lOS 


ress  of  the  embryo.  Special  points  will  be  considered,  ei-  ,er  in 
a  separate  chapter  now,  or  deferred  for  treatment  in  tb<  )ody 
of  the  work  from  time  to  time,  as  they  seem  to  throw  light 
upon  the  subjects  under  discussion. 


I 


DEVELOPMENT    OF 


MO-froBtal 
vlaoenl 


lue  object  (Fo«tM- and 
foMa.    p.  H,  cerebral 


al  pncem;  m, 
fold  (mandlbu- 


ned  descriptions 
inbsequent  prog- 


acA 


-L. 
B. 


cMFoater  and  Balfour), 
■tricle  (thalamenoepha- 
ebellum ;  IV.  V,  tovar& 
nn,  superior  maxillary 
re;  FT/,  eeventh  nerve; 
itkm  of  tlieae  ner*e«  la 
wing :  H.  L,  Und-Umb. 
od  of  Minatieat  Jk  5S. 


THE    VASCULAB  SYSTEM  IN  VERTE- 
BRATES. 


This  subject  has  been  incidentally  considered,  but  it  is  of 
such  importance  morphological,  physiological,  and  pathological, 
as  to  deserve  special  treatment. 

In  the  earliest  stages  of  the  circulation  of  a  vertebrate  the 
arterial  system  is  made  up  of  a  pair  of  arteries  derived  from  the 
single  btUbus  arteriostts  of  the  heart,  which,  after  passing  for- 
ward, bends  round  to  the  dorsal  side  of  the  pharynx,  each  giving 
off  at  right  angles  to  the  yelk-sac  a  vUeUine  artery ;  the  aortee 
unite  dorsally,  then  again  separate  and  become  lost  in  the  pos- 
terior end  of  the  embryo.  The  so-called  arches  of  the  aorta 
are  large  branches  in  the  anterior  end  of  the  embryo  derived 
from  the  aorta  itself. 

The  venous  system  corresponding  to 'the  above  is  composed 
of  anterior  and  posterior  pairs  of  longitudinal  (cardinal)  veins, 
the  former  (jugular,  cardinal)  uniting  with  the  posterior  to 
form  a  common  trunk  {dtu:tiis  Cuvieri)  by  which  the  venous 
blood  is  returned  to  the  heart.  The  blood  from  the  posterior 
part  of  the  yelk-sac  is  collected  by  the  vUeUiiie  veins,  which 
terminate  in  the  median  sinus  venosiis. 

The  Lattr  BtagM  of  tlw  Fatal  OinalatioA.— Gorrec^nding  to 
the  number  of  visceral  arches  five  pairs  of  aortic  arches  i&rise ; 
but  they  do  not  exist  together,  the  first  two  having  undergone 
more  or  less  complete  atrophy  before  the  others  appear.  Figs. 
119, 120  convey  an  idea  of  how  the  permanent  forms  (indicated 
by  darker  shading)  stand  related  to  the  entire  system  of  vessels 
in  different  groups  of  animals.  Thus,  in  birds  the  right  (fourth) 
aortic  arch  only  remains  in  connection  with  the  aorta,  the  left 
forming  the  subclavian  artery,  while  the  reverse  occurs  in  mam- 
mals.   The  fifth  arch  (pulmonary)  always  supplies  the  lungs. 

The  arrangement  of  the  principal  vessels  in  the  bird,  mam- 
mal, etc.,  is  represented  on  page  104.  In  mammals  the  two 
primitive  anterior  abdominal  {allantoic)  veins  develop  early 
and  unite  in  front  with  the  vitelline ;  but  the  right  allantoic 
vein  and  the  right  vitelline  veins  soon  disappear,  while  the  long 


104 


ANIMAL  PHTSIOLOGT. 


common  trunk  of  the  allantoic  and  vitelline  veins  {ductus  veno- 
sus)  passes  through  the  liver,  where  it  is  said  the  ductus  veno- 


1. 


Flo.  110.— Dfaurama  of  the  aortic  archea  of  mamnuU  (Londoia  aiid  Stirling,  after  Batlike). 
I.  Arterial  trunk  with  one  pair  of  arehea,  and  an  indication  where  the  aeoond  and  third 
paira  will  develop.  8.  Ideal  ataoe  of  Atc  oomiriete  archea ;  t^  fourth  clefta  are  abown  on 
the  left  aide.  &  The  two  anterior  paira  of  archea  have  dlaappeared.  4.  Transition  to  the 
flnal  tttLge.  A,  aortic  arch ;  ad,  doraal  aorta ;  ax,  aubclavlan  or  axillair  artery ;  Ce.  ex- 
ternal carotid  ;  Ci,  internal  carotkl ;  dB,  ductua  arterioaua  Botalll ;  P,  pulmonary  artery ; 
8,  aulMilaTian  artery ;  to,  truncua  arterioaum ;  «,  vertebral  artery. 

BUS  gives  oflf  and  receives  branches.  The  ductus  venosus  Aran- 
tii  ])ersists  throughout  life.  (Compare  the  various  figures  illus- 
trating the  circulation.) 


Fia.  190.— Diagram  HhtimWinr  tnnaf  ormatlona  of  aortlo  archea  in  a  liaard.  A ;  a  anake,  B ; 
a  bbd,  0 ;  a  mammaL  D.  Seen  from  below.  (Haddon,  after  Bathke.)-  a,  internal  caro- 
tid ;  b,  external  carotid ;  c,  common  carotid.  A.  d,  ductua  Botalll  between  the  third  and 
fourth  archea ;  e,  right  aortlo  arch ;  /,  aubdavlan ;  a,  doraal  aorta ;  k,  left  aortic  arch  : 
i.  pulmonary  artery :  Ic,  rudiment  of  the  ductua  Botalu  between  the  jMilmonary  artery  and 
the  aortic  archea.  B.  d,  right  aortic  arch ;  e,  vertebral  artery ;  /,  left  aortic  ardii ;  h, 
nulmonary  artery ;  i,  ductua  Botalll  of  the  latter.  C.  d,  origin  of  aorta ;  e,  fourth  arch  of 
the  right  aide  (root  of  doraal  aortat:  /,  right  aubclavian ;  g,  doraal  aorta :  h,  left  aubclavlan 
(fourth  arch  of  the  left  aide) :  <,  pulmonary  artery ;  k  and  i,  right  and  lefi  ductua  Botalll 
ot  the  pulmonary  arteriea.  D.  a,  origin  of  aorta ;  e,  fourth  arch  of  the  left  aide  (root  of 
doraal  aorta) :  /,  doraal  aorta ;  g,  left  vertebral  artery ;  K,  left  aubclavian ;  i,  right  aub- 
clavlan (fourth  arch  of  the  right  aide) ;  ie,  right  vertebral  artery ;  (,  continuation  of  the 
right  aubclavian  ;  m,  pulmomuy  ar^iy ;  n,  duotua  Botalli  of  the  latter  (uaually  tenned 
dttettM  ot-terionM). 


t  Uaard.  A ;  s  make,  B ; 
thke.)-  a,  internal  oaro- 

between  the  third  and 
ta ;  ft,  left  aortic  arch  : 
le  pulmonary  artery  and 

/,  left  aortic  ardii ;  h. 
aorta ;  «,  fourth  arch  of 
M>rta :  A,  left  Bubolavlan 
>  and  left  ductus  Botalli 

of  the  left  side  (root  of 
ubclavian ;  i,  right  nib- 

;  (,  continuation  of  the 
)  latter  (umalljr  termed 


DEVELOPMENT  OP  THE  VASCULAR  SYSTEM. 


105 


With  the  development  of  the  placenta  the  allantoic  circula- 
tion renders  the  vitelline  subordinate,  the  vitelline  and  the  larger 
mesenteric  vein  forming  the  portal.  The  jiortal  vein  at  a  later 
period  joins  one  of  the  vena  advehentea  of  the  allantoic  vein. 

At  first  the  vena  cava  inferior  and  the  ductus  venosus  enter 
the  heart  as  a  common  trunk.  The  ductus  venosus  Arantii 
becomes  a  small  branch  of  the  vena  cava. 

The  allantoic  vein  is  finally  represented  in  its  degenerated 
form  as  a  solid  cord  {round  ligament),  the  entire  venous  suj)- 
ply  of  the  liver  being  derived  from  the  portal  vein. 

The  development  of  the  heart  has  already  been  traced  in  the 
fowl  up  to  a  certain  point.  In  the  mammal  its  origin  and  early 
progress  are  similar,  and  its  further  histoiy  may  be  gathered 
from  the  following  series  of  representations. 

In  the  fowl  the  heart  shows  the  commencement  of  a  division 
into  a  right  and  left  half  on  the  third  day,  and  about  the 
fourth  week  in  man,  from  which  fact  alone  some  idea  may  be 
gained  as  to  the  relative  rate  of  development.    The  division 


Fia.  128. 


Flo.  in. 

Fio.  181.— Development  of  the  heart  in  the  human  embryo,  from  the  fourth  to  the  sixth  wedt. 
A.  Emtnyo  of  four  weeks  (KOUiker,  after  Ooste).  B,  anterior,  C,  portertor  views  of  the 
heart  of  an  embryo  of  six  weeks  (KOUiker,  after  Eckwr).    o.  upper  Ijinit  of  buccal  cavity ; 

c.  buccal  cavity ;  6,  lies  between  the  ventral  ends  of  second  and  third  branchial  arches ; 

d,  buds  of  upper  limbs ;  I,  Uver ;  /,  intestine  rl. juperior  vena  cava ;  1',  left  superior  vena 
cava ;  1",  openioK  of  inferior  vena  cava ;  8,  8',  right  and  left  auricles ;  3,  8',  right  and  left 
ventricles ;  4,  aortic  bulb.  .       „     _t  >  ,•  >    <•    ..  i  . 

Fig.  188.— Human  embryo  of  about  three  weeks  (Allen  Thomson),  uv,  yelk-sac;  ai,  allantois; 
am,  amnion ;  ae,  anterior  extremity ;  pe,  posterior  extremity. 

is  effected  by  the  outgrowth  of  a  septum  from  the  ventral  wall, 
which  rapidly  reaches  the  dorsal  side,  when  the  double  ven- 
tricle thus  formed  communicates  by  a  right  and  left  auriculo- 
ventricular  opening  with  the  large  and  as  yet  imdivided  auricle. 


tUMIlJ'.-iJ     I  '"-■»'i™'A''»WWIBB« 


!i«Mm.t.<i:,.i,'im»-li" 


106 


ANIMAL  PHYSIOLOGY. 


Later  an  incomplete  septum  forms  similar  divisions  in  the  auri- 
cle ;  the  aperture  {foramen  m^ale)  left  by  the  imperfect  growth 
of  this  wall  persisting  throughout  foetal  life. 

The  Eustachian  valve  arises  on  the  dorsal  wall  of  the  right 
auricle,  between  the  vena  cava  inferior  and  the  right  and  left 
vensB  cavsB  superiores ;  but  in  many  mammals,  among  which  is 
man,  the  left  vena  cava  superior  disappears  during  fcetal  life. 

For  the  present  we  may  simply  say  that  the  histories  of  the 
development  of  the  heart,  the  blood-vessels,  and  the  blood  itself 
are  closely  related  to  each  other,  and  to  the  nature  and  changes 
of  the  various  methods  in  which  oxygen  is  supplied  to  the  blood 
and  tissues,  or,  in  other  words,  to  the  development  of  the  respir- 
atory system. 


THE  DEVELOPMENT  OF  THE  HBOOENITAL  SYSTEM. 

Without  knowing  the  history  of  the  organs,  the  anatomical 
relations  of  parts  with  uses  so  unlike  as  reproduction  on  the  one 
hand  and  excretion  on  the  other,  can  not  be  comprehended ;  nor, 
as  will  be  shortly  made  clear,  the  fact  that  the  same  part  may 
serve  at  one  time  to  remove  waste  matters  (urine)  and  at  an- 
other the  generative  elements. 

The  vertebrate  excretory  system  may  be  divided  into  three 
parts,  which  result  from  the  differentiation  of  the  primitive 
kidney  which  has  been  effected  during  the  slow  and  gradual 
evolution  of  vertebrate  forms : 

1.  The  head-kidney  {pronephros). 

2.  The  Wolflftan  body  {meaonephros). 

3.  The  kidney  proper,  or  metanephroa. 

But  in  this  instance,  as  in  others,  to  some  of  which  allusion 
has  already  been  made,  these  three  parts  are  not  functional  at 
the  same  time.  The  pronephros  arises  from  the  anterior  part 
of  the  segmental  duct,  pronephric  duct,  duct  of  primitive  kid- 
ney, and  archinephric  duct,  and  in  the  fowl  is  apparent  on  the 
third  day;  but  the  pronephros  is  best  developed  in  the  ich- 
thyopsida  (fishes  and  amphibians).  A  vascular  process  from 
the  peritoneum  {glomendua)  projects  into  a  dilated  section  of 
the  body  cavity,  which  is  in  part  separated  from  the  rest  of  this 
cavity  {ccelom).  This  process,  together  with  the  segmental 
duct,  now  coiled,  and  certain  short  tubes  developed  from  the 
original  duct,  make  up  the  pronephros.  The  segmental  duct 
opens  at  length  into  the  cloaca. 


iaMififiififiiiTiiiii  I 


isions  in  the  auri- 
imperfect  growth 

I  wall  of  the  right 
the  right  and  left 
s,  among  which  is 
uring  foetal  life, 
be  histories  of  the 
ad  the  blood  itself 
ature  and  changes 
pplied  to  the  blood 
mentof  therespir- 


ITAL  SYSTEM. 

,ns,  the  anatomical 
duction  on  the  one 
jmprehended ;  nor, 
the  same  part  may 
(urine)  and  at  an- 

divided  into  three 

a  of  the  primitive 

slow  and  gradual 


)  of  which  allusion 
B  not  functional  at 
n  the  anterior  part 
jt  of  primitive  kid- 
is  apparent  on  the 
reloped  in  the  ich- 
cular  process  from 
a  dilated  section  of 
Tom  the  rest  of  this 
ith  the  segmental 
ieveloped  from  the 
he  segmental  duct 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM      107 

The  meacmephroa  (Wolffian  body),  though  largely  developed 
in  all  vertebrates  during  foetal  Ufe,i8nofc  a  persistent  excretory 
organ  of  adult  life. 


■omatlc ;  and  «p,  qtUnchnlc,  OMioblaA 

In  the  fowl  recent  investigation  has  shown  that  the  Wolffian 
(segmental)  tubes  originate  from  outgrowths  of  the  Wolffian 


t  «   i 


Flo.  194. 


Fia.l>6. 


duct  and  also  from  an  intermediate  cell-mass,  from  which  lat- 
ter the  Malpighian  bodies  take  rise.  The  tubes,  at  first  not  con- 


•WMP 


108 


ANIMAL  PHYSIOLOGY. 


nected  with  the  duct,  finally  join  it.  This  brgan  is  continuous 
with  the  pronephros ;  in  fact,  all  three  (pronephros,  mesone- 
phros,  and  metanephros)  may  be  regarded  as  largely  continua- 
tions one  of  another. 

The  metanephros,  or  kidney  proper,  arises  from  mesoblast 
at  the  posterior  part  of  the  WolflBan  body.    The  ureter  origi- 


Fta.  198.— Section  of  the  Intermediate  oell-nuMi  of  fourth  day  (Foster  and  Balfonr,  after  Wal- 
deyer).  1  »  1(10.  m,  mesentery ;  L,  aomatopleure ;  a',  portion  of  the  oerminal  epitheUum 
from  the  dnot  of  MtUler  to  formed  by  involution ;  a,  thickened  portion  of  the  serminal 
epithelium,  in  which  tbo  primitive  ova  C  and  o  are  lying ;  E,  modified  meaoblaat  which 
will  form  the  stroma  of  the  orary ;  WK,  WoUHan  N>dy ;  y,  WoUBan  duct 

nates  first  from  the  hinder  portion  of  the  Wolffian  duct.  In 
the  fowl  the  kidney  tubules  bud  out  from  the  ureter  as  rounded 
elevations.  The  ureter  loses  its  connection  with  the  Wolffian 
duct  and  opens  independently  into  the  cloaca. 

The  following  account  will  apply  especially  to  the  higher 
vertebrates : 

The  segmental  (archinephric)  duct  is  divided  horizontally 
into  a  dorsal  or  Wolffian  (mesonephric)  duct  and  a  ventral  or 
Miillerian  duct.  The  Wolffian  duct,  as  we  have  seen,  develops 
into  both  ureter  and  kidney  proper. 

To  carry  the  subject  somewhat  further  back,  the  epithelium 
lining  the  coelom  at  one  region  becomes  differentiated  into  col- 
umns or  cells  {germinal  epitheUum)  which  by  involution  into 
the  underlying  mesoblast  forms  a  tubule  extending  from  before 
backward  and  in  close  relation  with  the  Wolffian  duct,  thus 


is  continuous 
>hros,  mesone- 
fely  continua- 

om  mesoblast 
I  ureter  origi- 


Balfonr,  after  Wal- 
terminal  epithelium 
Ion  of  the  germiiutl 
ed  meaoblaat  which 
uct. 


San  duct.    In 

9r  as  rounded 

the  Wolffian 

lo  the  higher 

horizontally 
a  ventral  or 
een,  develops 

le  epithelium 
ited  into  col- 
irolution  into 
f  from  before 
in  duct,  thus 


THE  DEVELOPMENT  OF  THE  UROGENITAL  SYSTEM.      109 

forming  the  Miillerian  dv.  t  by  the  process  of  cleavage  and 
separation  referred  to  on  preceding  page. 


Fia.  187.— DiMtrammatlo  repreMntaUon  of  titejenltal  orgww  ot  a  human  embryo  prevlmis  to 
•ezual  diSnction  (Allen  Thomaon).  -W,  woUXan  body :  0e,  genital  cmd ;  m,  MOUeriMi 


■inus ;  cp,  tiAorit  or  penia ;  i.[  intestine  j  ct. 


duct;  W,  Wolffian  duct:  no,  urogemuu  auius.  •!»,  ouwrui  ur  yeitm,  ..  luijmuw ,  t., 
cloaca ;  if,  part  from  which  Oe  ncrotum  or  labia  majora  are  developed ;  ot,  origin  of  the 
ovary  or  teaUole  reqwcUveW;  x,  part  of  the  WoUBan  body  dereloped  liter  bito  theconi 
vaaouloai ;  8,  ureter ;  4,  bladder ;  S,  uracfaua. 

The  future  of  the  Miillerian  and  Wolffian  ducts  varies  ac- 
cording to  the  sex  of  the  embryo. 


Fm, 


.  las.— Diaxram  of  the  mammalian  type  of  male  aenial  organs  (after  Qualn).  Compare 
with  FlgiTlW.  1».  C,  Oowper's  glaiul  ot  one  aide ;  ep,  corpora  OAvemoaa  pento,  cut^rt ; 
e,  capuTepididymU  to,  gunemamdum ;  i,  rectum ;  m,  hydatid  of  Morngnl,  the  perstatent 
anlSlor  end  of  the  Mmierian  duct,  the  conjoint  posterior  ends  of  whfiih  form  the  uterua 
maacullnua :  pr,  prostate  gland ;  «,  scrotum ;  <m.  corpus  spongiosum  urethre ;  t-.tustU 
(testicle)  in  tne  place  of  its  original  formation.  The  dotted  line  indicates  the  direction  in 
which  the  testis  and  epididynw  change  place  in  their  descent  from  the  abdomen  mto  the 
aorotum :  vd,  vas  defWrens ;  vk.  vas  aberrans ;  m,  wrioula  aeminalis ;  W,  remnants  ot 
IvSinM  \x)dy  (the  orgwt  of  Qin^te  or  paradidymis  of  Waldeyer) ;  a,  4, 6,  as  in  Fig.  in. 


no 


ANIMAL  PHYSIOLOGY. 


In  the  male  the  WolflBan  duct  persists  as  the  vas  deferens ; 
in  the  female  it  remains  as  a  rudiment  in  the  region  near  the 
ovary  (hydatid  of  Morgagni).  In  the  female  the  Mlillerian 
duct  becomes  the  oviduct  and  related  parts  (uterus  and  vagina) ; 
in  the  male  it  atrophies.  One,  usually  the  right,  also  atrophies 
in  female  birds.  The  sinus  pocularis  of  the  prostate  is  the  rem- 
nant in  the  male  of  the  fused  tubes. 

The  various  forms  of  the  generative  apparatus  derived  from 
the  Miillerian  ducts,  as  determined  by  different  degrees  of  fu- 
sion, etc.,  of  parts,  may  be  learned  from  the  accompanying 
figures. 

In  both  sexes  the  most  posterior  portion  of  the  WolflBan 
duct  gives  rise  to  the  metanephros,OTvrha,t  becomes  the  perma- 


fto.  IW.— Ptognwi  of  the  iiuhtiiiuJIm  tame  of  fenuJe  ■wnuJ  onauM  (»ftor  Quato).  The  dotted 
linM  In  one  figure  indicate  f  unctloniU  onrana  in  the  other.  O.glaiid  of  Bartholin  (Oownu-'a 
riand) :  c.  e,  ooroua  oavemoaum  clitorldb ;  dO,  rematos  of  the  left  WoUBan  duct,  whksh 
niur  peratat  as  the  duot  of  Oaertner ;  /,  abdominal  opeidng  of  left  Fallopian  tube ;  a, 
round  lisament  (oorreapondlng  to  the  gubemaoulum) :  h,  hymen ;  i, rectum :  I, labium; 
m,  cut  lUloplan  tube  (OTiduot,  or  Mttllerlan  duct)  of  the  rlMit  aide ;  n,  njrmpha ;  o,  left 
orary ;  no,  parovarium ;  te,  Taacular  bulb  or  corpua  aponfloaum :  «,  uterua ;  v,  vulva ; 
va,  vagina :  W,  acattwed  remalna  of  Wolfflan  tubes  (paroBphoron) ;  le,  cut  end  of  yan- 
iahed  right  Wollllan  duct;  S,  ureter;  4,  Madder  paaaing  below  into  the  uretha;  5,  uraohua, 
or  remnant  of  stalk  of  allantoia.  ^ 

nent  kidney  and  ureter ;  in  the  male  also  to  the  vas  deferens, 
testicle,  vas  aberrans,  and  seminal  vesicle. 

The  ovary  has  a  similar  origin  to  the  testicle ;  the  germinal 
epithelium  furnishing  the  cells,  which  are  transformed  into 
Graafian  follicles,  ova,  etc.,  and  the  mesoblast  the  stroma  in 
which  these  structures  are  imbedded. 

In  the  female  the  parovarium  remains  as  the  representative 
of  the  atrophied  Wolffian  body  and  duct. 

The  bladder  and  uraohus  are  both  remnants  of  the  formerly 
extensive  allantois.    The  final  forms  of  the  genito-urinary  or- 


rt<#r^!iaWfl«MlWMimHil«MMMI^^ 


MHlHWfilliiiMiit  iaaffer; 


vas  deferens ; 
igion  near  the 
the  Mlillerian 
s  and  vagina) ; 
also  atrophies 
ite  is  the  rem- 

j  derived  from 
degrees  of  fu- 
Eiccompanying 

the  Wolffian 
les  the  perma- 


trOuain).  The  dotted 
f  BarthoUn  (Oowper'e 
WolflUui  duct,  whioh 
ft  FallopUui  tube ;  g, 
i,  rectum :  I,  ktbium ; 
;  n,  njrmpha ;  o,  left 
«,  uterua ;  v,  vulva ; 
I ;  w,  cut  end  of  van- 
le uretba;  5,  uraohua. 


)  vas  deferens, 

;  the  germinal 
nsformed  into 
the  stroma  in 

representative 

»f  the  formerly 
ito-urinary  or- 


THB  DEVELOPMENT  OP  THE  UBOGBNITAL  SYSTEM.      HI 

gans  arise  by  differentUtion,  fusion,  and  atrophy:  thus,  the 
cloaca  or  common  cavity  of  the  genito-urinary  ducts  is  divided 
by  a  septum  (the  perineum  externally)  into  a  genito-urinary 
and  an  intestinal  (anal)  part;  the  penis  in  the  male  and  the 
corresponding  clitoris  in  the  female  appear  in  the  region  of  the 
cloaca,  as  outgrowths  which  are  followed  by  extension  of  folds 
of  integument  that  become  the  scrotum  in  the  one  sex  and  the 
labia  in  the  other. 

The  urethra  arises  as  a  groove  in  the  under  surface  of  the 
penis,  which  becomes  a  canal.  The  original  opening  of  the 
urethra  was  at  the  base  of  the  penis. 


AL 


Ah. 


Fw.  180. 


Fio.  m. 


Fm.  in. 


Flo.  in. 


Fioa.  1»  to  in.-Dla««ma  Olurtratliig  the  evohittoii  o«  the  poaterior  paaiagM  (after  Landoia 

and  StirUnK).  . ..     ^  _ 

Fio.  iaO.—AUimtoUcontinuoua  with  rectum. 

fS-  ISiZgS^cSSl  to  nuOe,  before  the  doauw  of  thofoldaaf  the  groove  on  the  porte- 

rior  aide  of  the  pwila. 
Fm.  l»-E«»^«"^52SSS£2:,m-  ALL.  allantoia:  B,  bladder;  C,  penla;  CL.  cloaca; 
^  CTSSSr  duSt  ;^r^^Sr  h^'^O^SSmi^^ ;  SV,  'unie^tal  rinu. ;  K.  vaa 

dMterens  to  Fig.  in,  vagtoa  to  Fig.  18B. 

In  certain  cases  development  of  these  parts  is  arrested  at 
variouD  stages,  from  which  result  abnormalities  frequently  re- 
quiring  interference  by  the  surgeon. 

The  accounts  of  the  previous  chapters  do  not  complete  the 
history  of  development.  Certain  of  the  remaining  subjects 
that  are  of  special  interest,  from  a  physiological  point  of  view, 
will  be  referred  to  again;  and  in  the  mean  time  we  shall 
consider  rather  briefly  some  of  the  physiological  problems  of 
this  subject  to  which  scant  reference  has  as  yet  been  made. 
Though  the  physiology  of  reproduction  is  introduced  here,  so 
that  ties  of  natural  connection  may  not  be  severed,  it  may 
very  well  be  omitted  by  the  student  who  is  dealing  with  embry- 


■Wtliw 


112 


f 

AMIUAL  PHYSIOLOGY. 
A 


Fig.  IM.— Various  forma  of  Duunmaltan  uteri.  A.  Ornlthoi^yiichui.  B.  Didelphys  donlgem. 
C.  Phalantrteta  Tulidiia.  O.  Double  utenu  and  TOKina;  numan  anomaly.  E.  I«puacunl- 
culua  (rabbit),  uterua  duplex.  F.  Uterus  bloomis.  Q.  Uterus  Mpartitus.  H.  Uterus 
simplex  (human),  o,  anus ;  eJ,  cloaca ;  o.  d,  oviduct ;  o.  *,  os  tlncse  (os  uteri)  5  o»,  ovary ; 
r,  rectum :  t,  vafcinal  septiun ;  11. 6,  urinary  bladder ;  «r,  uret«r ;  w.  o,  orifice  of  same ; 
iu,  urogenital  sinus ;  irf,  uterus;  v,  vagina;  v.  c,  vaginal  oaeoum  (Haddon). 

ology  for  the  first  time,  and  in  any  case  should  be  read  again 
after  the  other  functions  of  the  body  have  been  studied. 


The  Physiological  Aspects  of  Development. 

According  to  that  law  of  rhythm  which,  js  we  have  seen, 
prevails  throughout  the  world  of  animated  nature,  there  are 
periods  of  growth  and  progress,  of  quietude  and  arrest  of  devel- 
opment ;  and  in  vertebrates  one  of  the  most  pronounced  epochs 
— in  fact,  the  most  marked  of  all — is  that  by  which  the  young 
organism,  through  a  series  of  rapid  stages,  attains  to  sexual 
maturity. 

While  the  growth  and  development  of  the  generative  or- 
gans share  to  the  greatest  degree  in  this  progress,  other  parts  of 
the  body  and  the  entire  being  participate. 

So  great  is  the  change  that  it  is  common  to  indicate,  in  the 
case  of  the  human  subject,  the  developed  organism  by  a  new 
name— the  "  boy  "  becomes  the  "  man,"  the  "  girl "  the  "  woman." 
Relatively  this  is  by  far  the  most  rapid  and  general  of  all  the 
transformations  the  organism  undergoes  during  its  extra-uter- 
ine life.  In  this  the  entire  body  takes  part,  but  very  unequally. 
The  increase  in  stature  is  not  proportionate  to  the  increase 
in  weight,  and  the  latter  is  not  so  great  as  the  change  in  form. 
The  modifications  of  the  organism  are  localized  and  yet  affect 
the  whole  being.    The  outlines  become  more  rounded ;  the  pel- 


liiil  llliMnMllllMil 


Mdelplqrs  donlgem. 
iljr.  E.  L«ptiacuni- 
utitus.  H.  Uterus 
I  uteri) ;  ov,  ovaiy ; 
o,  orifice  of  same ; 
Ion). 

be  read  again 
ludied. 

PHKNT. 

ire  have  seen, 
ire,  there  are 
Test  of  devel- 
mnced  epochs 
ch  the  young 
ins  to  sexual 

fenerative  or- 
other  parts  of 

idioate,  in  the 
ism  by  a  new 
the  "woman." 
)ral  of  all  the 
its  extra-uter- 
)ry  unequally. 
>  the  increase 
ange  in  form, 
and  yet  affect 
ided ;  the  pel- 


THE  DEVELOPMENT  OP  THE  UROGEmTAL  SYSTEM.      118 

vis  in  females  alters  in  shape ;  not  only  do  the  generative  organs 
themselves  rapidly  undergo  increased  development,  but  certain 
related  glands  (mammee)  participate;  hair  appears  in  certain 
regions  of  the  body  \  the  larynx,  especially  in  the  male,  under- 
goes enlargement  and  change  in  the  relative  size  of  parts,  re- 
sulting in  an  alteration  of  voice  (bi'eaking  of  the  voice),  etc. — 
all  in  conformity  with  that  excess  of  nutritive  energy  which 
marks  this  biological  epoch. 

(Correlated  with  these  physical  changes  are  others  belonging 
to  the  intellectual  and  moral  (psychic)  nature  equally  impor- 
tant, and,  accordingly,  the  future  being  depends  largely  on  the 
full  and  unwarped  developments  of  these  few  year£(^ 

Sexual  maturity,  or  the  capacity  to  furnish  ripe  sexual  ele- 
ments (cells),  is  from  the  biological  standpoint  the  most  impor- 
tant result  of  the  onset  of  that  period  termed,  as  regards  the 
human  species,  puberty. 

The  age  at  which  this  epoch  is  reached  varies  with  race, 
sex,  climate,  and  the  moral  influences  which  envelop  the  indi- 
vidual. In  temperate  regions  and  with  European  races  pu- 
berty is  reached  at  from  about  the  thirteenth  to  thia  eighteenth 
year  in  the  female,  and  rather  later  in  the  male,  in  whom  de- 
velopment generally  is  somewhat  slower. 

Menstruatiok  Ain>  Ovulation. 

(In  all  vertebrates,  at  periods  recurring  with  great  regu- 
larity, the  generative  organs  of  the  female  manifest  unusual 
activity.  This  is  characterized  by  increased  vascularity  of  the 
ovary  and  adjacent  parts;  with  other  changes  dependent  on 
this,  and  that  heightened  nerve  influence  which,  in  the  verte- 
brate, seems  to  be  inseparable  from  all  important  functional 
changes.  Ovulation  is  the  maturation  and  discharge  of  ova 
from  the  Graafian  follicles.  The  latter,  reaching  the  exterior 
zone  of  the  ovary,  becoming  distended  and  thinned,  burst  ex- 
ternally and  thus  free  the  ovum.  The  follicles  being  very  vas- 
cular at  this  period,  blood  escapes,  owing  to  this  rupture,  into 
the  emptied  capsule  and  clots ;  and  as  a  result  of  organization 
and  subsequent  degeneration  undergoes  a  certain  series  of 
changes  dependent  on  the  condition  of  the  ovary  and  adjacent 
parts,  which  varies  according  as  the  ovum  has  been  fertilized 
or  liot.  When  fertilization  occurs  the  Graafian  follicle  under- 
goes changes  of  a  more  marked  and  lasting  character,  becom- 
ing a  true  corpus  luieum  of  pregnancy, 
8 


"i;il»iM!il»Wa»>i»iJii»i»»«»«i«i>i»ii.i<ilWl*' 


mmt 


114 


AKIMAL  PHTSIOLOOT. 


The  ovQin  in  the  fowl  is  fertilized  in  the  upper  part  of  the 
oviduct ;  in  the  manunal  mostly  in  this  region  also,  as  is  shown 
by  the  site  of  the  embryos  in  those  groups  of  animals  with  a 
two-homed  uterus,  and  the  occasional  occurrence  of  tubal  preg- 
nancy in  woman.  But  this  is  not,  in  the  human  subject  at 
least,  invariably  the  site  of  impregnation.  After  the  ovum  has 
been  sbt  free,  as  above  described,  it  is  conveyed  into  the  ovi- 
duct (Fallopian  tube),  though  exactly  how  is  still  a  matter  of 
dispute :  some  holding  that  the  current  produced  by  the  action 
of  the  ciliated  cells  of  the  Fallopian  tube  suffices ;  others  that 
the  ovum  is  grasped  by  the  fimbriated  extremity  of  the  tube  as 
part  of  a  co-ordinated  act.  It  is  likely,  as  in  so  many  other 
instances,  that  both  views  are  correct  but  partial ;  that  is  to 
say,  both  these  methods  are  employed.  The  columnar  ciliated 
cells,  lining  the  oviduct,  act  so  as  to  produce  a  current  in  the 
direction  of  the  uterus,  thus  assisting  the  ovum  in  its  passage 
toward  its  final  resting  place. 

Kaiiitniatioii. — As  a  part  of  the  general  activity  occurring 
at  this  time,  the  uterus  manifests  certain  changes,  chiefly  in 
its  internal  mucous  lining,  in  which  thickening  and  incr^ised 


Fio.  MS.— Diagnun  of  the  bunum  uteim  Jwt 
before  menatnuttion.  The  ahaded  por- 
tion repreaenta  the  muooua  membrane 
(Hart  and  Barbour,  after  J.  WUUanui). 


Tta.  186.— Utema  after  menatniatlo^  has  just 
ceaaed.  The  cvrttr  of  the  bodr  of  the 
uterui  la  auppoaed  to  hare  been  deprived 
of  muooua  membrane  (J.  WlUiama). 


vascularity  are  prominent.    A  flow  of  blood  from  the  uterus 
in  the  form  of  a  gentle  oozing  follows;  and  as  the  superficial 


smam 


er  part  of  the 
o,  as  is  shown 
dmals  with  a 
of  tubal  preg- 
an  subject  at 
the  ovum  has 
into  the  ovi- 
[1  a  matter  of 
by  the  action 
9 ;  others  that 
of  the  tube  as 
3  many  other 
ial ;  that  is  to 
imnar  ciliated 
urrent  in  the 
in  its  passage 

ity  occurring 
l^es,  chiefly  in 
and  incr^wed 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM,      lift 

parts  of  the  mucous  lining  of  the  uterus  undergo  softening 
and  fatty  degeneration,  they  are  thrown  off  and  renewed  at 
these  periods  {catamenia,  menses,  etc.),  provided  pregnancy 
does  not  take  place.  In  mammals  below  man,  in  their  nat- 
ural state,  pregnancy  does  almost  invariably  take  place  at 
such  times,  hence  this  exalted  activity  of  the  mucous  coat  of 
the  uterus,  in  preparation  for  the  re«3eption  and  nutrition  of 
the  ovum,  is  not  often  in  vain.  In  the  human  subject  the 
menses  appear  monthly ;  pregnancy  may  or  may  not  occur,  and 
consequently  there  may  be  waste  of  nature's  forces ;  though 
there  is  a  certain  amount  of  evidence  that  menstruation  does 
not  wholly  represent  a  loss;  but  that  it  is  largely  of  that  char< 
acter  among  a  certain  class  of  women  is  only  too  evident.  As 
can  be  readily  understood,  the  catamenial  flow  may  take  place 
prior  to,  during,  or  after  the  rupture  of  the  egg-capsule. 

As  the  uterus  is  well  supplied  with  glands,  during  this 
period  of  increased  functional  activity  of  its  lining  membrane, 
mucus  in  considerable  excess  over  the  usual  quantity  is  dis- 
charged ;  and  this  phase  of  activity  is  continued  should  preg- 
nancy occur. 

All  the  parts  of  the  generative  organs  axe  supplied  with 
muscular  tissue,  and  with  nerves  as  well  as  blood-vessels,  so 
that  it  is  possible  to  imderstand  how,  by  the  influence  of  nerve- 
centers,  the  various  events  of  ovulation,  menstruation,  and 
those  that  follow  when  pregnancy  takes  place,  form  a  related 
series,  very  regular  in  their  succession,  though  little  prominent 
in  the  consciousness  of  the  individual  animal  when  normaL 


/I 


lenatnuitlo^  has  Just 
or  the  bodrof  the 
>  hare  been  deprived 
« (J.  WlUUnnsr 


>m  the  uterus 
bhe  superficial 


The  Nutrition  of  the  Ovum  (oospbrm). 

This  will  be  best  understood  if  it  be  remembered  that  the 
ovum  is  a  cell,  undifferentiated  in  most  directions,  and  thus  a 
sort  of  amoeboid  organism.  In  the  fowl  it  is  known  that  the 
cells  of  the  primitive  germ  devour,  amoeba-like,  the  yelk-cells, 
while  in  the  mammalian  oviduct  the  ovum  is  surrounded  by 
abundance  of  proteid,  which  is  doubtless  utilized  in  a  somewhat 
similar  fashion,  as  also  in  the  uterus  itself,  until  the  embryonic 
membranes  have  formed.  To  speak  of  the  ovum  being  nour- 
ished by  diffusion,  and  especially  by  osmosis,  is  an  unnecessary 
assumption,  and,  as  we  believe,  at  variance  with  fundament^ 
principles;  for  we  doubt  much  whether  any  vital  process  is 
one  of  pure  osmosis.  As  soon  as  the  yelk-sac  and  allantois 
have  been  formed,  nutriment  is  derived  in  great  part  through 


116 


ANIMAL  PHTSIOLOOT. 


the  vessel-walls,  which,  it  will  be  remembered,  are  differentia- 
ted from  the  cells  of  the  mesoblast,  and,  it  may  well  be  as- 
sumed, have  not  at  this  early  stage  entirely  lost  their  amoeboid 
character.  The  blood-vessels  certainly  have  a  respiratory  func- 
tion, and  suffice,  till  the  more  complicated  villi  are  formed. 
The  latter  structures  are  in  the  main  similar  in  build  to  the 
villi  of  the  alimentary  tract,  and  are  adapted  to  being  sur- 
rounded by  similar  structures  of  maternal  origin.  Both  the 
maternal  crypts  and  the  foetal  villi  are,  though  complementary 
in  shape,  all  biit  identical  in  minute  structure  in  most  in- 
stances. In  each  case  the  blood-vessels  are  covered  superfi- 
cially by  cells  which  we  can  not  help  thinking  are  essential  in 
nutrition.  The  villi  are  both  nutritive  and  respiratory.  It  is 
no  more  difficult  to  understand  their  function  than  that  of  the 
cells  of  the  endoderm  of  a  polyp,  or  the  epithelial  coverings  of 
limgs  or  gills. 

Experiment  proves  that  there  is  a  respiratory  interchange 
of  gases  between  the  maternal  and  foetal  blood  which  nowhere 
mingle  physically.  The  same  law  holds  in  the  respiration  of 
the  ftjetus  as  in  the  mammals.  Oxygen  passes  to  the  region 
where  there  is  least  of  it,  and  likewise  carbonic  anhydride.  If 
the  mother  be  asphyxiated  so  is  the  foetus,  and  indeed  more 
rapidly  than  if  its  own  umbilical  vessels  be  tied,  for  the  mater- 
nal blood  in  the  first  instance  abstracts  the  oxygen  from  that 
of  the  foetus  when  the  tension  of  this  gas  becomes  lower  in  the 
maternal  than  in  the  foetal  blc>od ;  the  usual  course  of  affairs 
is  reversed,  and  the  mother  satisfies  the  oxygen  hunger  of  her 
own  blood  and  tissues  by  withdrawing  that  which  she  recently 
supplied  to  the  foetus.  It  will  be  seen,  then,  that  the  embryo  is 
from  the  first  a  parasite.  This  explains  that  exhaustion  which 
pregnancy,  and  especially  a  series  of  gestations,  entail&  True, 
nature  usually  for  the  time  meets  the  demand  by  an  excess  of 
nutritive  energy :  hence  many  persons  are  never  so  vigorous  in 
appearance  as  when  in  this  condition ;  often,  however,  to  be  fol- 
lowed by  corresponding  emaciation  and  senescence.  The  full 
and  frequent  respirations,  the  bounding  pulse,  are  succeeded  by 
reverse  conditions ;  action  and  reaction  are  alike  present  in  the 
animate  and  inanimate  worlds.  Moreover,  it  falls  to  the  parent 
to  eliminate  not  only  the  waste  of  its  own  organism  but  that  of 
the  foetus ;  and  not  infrequently  in  the  human  subject  the  over- 
wrought excretory  organs,  especially  the  kidneys,  fail,  entailing 
disastrous  consequences. 

The  digestive  functions  of  the  embryo  are  naturally  inact- 


HWwMBInn] 


re  differentia- 
y  well  be  as- 
heir  amoeboid 
piratory  func- 
i  are  formed. 
0.  build  to  the 
to  being  sar- 
in. Both  the 
jmplementary 
e  in  most  in- 
vered  superfi- 
,re  essential  in 
iratory.  It  is 
m  that  of  the 
I  coverings  of 

ry  interchange 
rhich  nowhere 
respiration  of 
to  the  region 
anhydride.  If 
1  indeed  more 
for  the  mater- 
gen  from  that 
as  lower  in  the 
urse  of  affaire 
hunger  of  her 
jh  she  recently 
the  embryo  is 
laustion  which 
entails.  True, 
y  an  excess  of 
so  vigorous  in 
rever,  to  be  f ol- 
>nce.  The  full 
e  succeeded  by 
)  present  in  the 
Is  to  the  parent 
ism  but  that  of 
ibject  the  over- 
ly fail,  entailing 

aturally  inact- 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.     II7 

ive,  the  blood  being  supplied  with  all  its  needful  constituents 
through  the  placenta  by  a  much  shorter  process ;  indeed,  the 
placental  nutritive  functions,  so  far  as  the  foetus  is  concerned, 
may  be  compared  with  the  removal  of  already  digested  material 
from  the  alimentary  canal,  though  of  course  only  in  a  general 
way.  During  foetal  life  the  digestive  glands  are  developing, 
and  at  the  time  of  birth  all  the  digestive  juices  are  secreted  in 
an  efficient  condition,  though  only  relatively  so,  necessitating  a 
special  liquid  food  (milk)  in  a  form  in  which  all  the  constituents 
of  a  normal  diet  are  provided,  easy  of  digestion. 


Fw.  187.— Hunwa  wrnit  or  embtTM  fiwm  tiM  MeoBd  to  Um  flfteenth  week  (natural  iriM),  Men 
ftom  the  left  Site,  the arctoS  bade  tamed  toward  the  ri^t.  (PrlndpaUy  after  Boker.). 
n, human  emhnro  ot  14  dare ;  m, of  8  weeks ;  JV,  of  4  weeln;  V.  or  B  weeke ;  VI,  ot  A 
weeks;  vn,o(7weeki;  ViuI,oC8weeka:  XO,  ot  It  weeks ;  ZV,  of  16  weeks. 

Bile,  inspissated  and  mized  with  the  dead  and  cast-off  epi- 
thelium of  the  alimentary  tract,  is  abundant  in  the  intestine  at 
birth  in  the  human  subject ;  but  bile  is  to  be  regarded  perhaps 
rather  in  the  light  of  an  excretion  than  as  a  digestive  fluid. 
The  skin  and  kidneys,  though  not  functionless,  are  rendered 
unnecessary  in  great  part  by  the  fact  that  waste  can  be  and  is 
withdrawn  by  the  placenta,  which  proves  to  be  a  nutritive,  re- 


MMi 


118 


ANIMAL  PHYSIOLOGY. 


spiratory,  and  excretory  organ ;  it  is  in  itself  a  sort  of  abstract 
Ctnd  brief  chronicle  of  the  whole  physiological  story  in  fcetal  life. 

All  of  the  fcetal  organs,  especially  the  muscles,  abound  in  an 
animal  starch  (glycogen),  which  in  some  way,  not  well  under- 
stood, forms  a  reserve  fund  of  nutritive  energy  which  is  pretty 
well  used  up  in  the  earlier  months  of  pregnancy.  We  may 
suppose  that  the  amoeboid  cells— all  the  undifferentiated  cells 
of  the  body — feed  on  it  in  primitive  fashion ;  and  it  will  not 
be  forgotten  that  the  older  the  cells  become,  the  more  do  they 
depart  from  the  simpler  habits  of  their  earlier,  cruder  existence ;  , 
hence  the  disappearance  of  this  substance  in  the  later  months 
of  foetal  life. 

In  one  respect  the  foetus  closely  resembles  the  adult:  it 
draws  the  pabulum  for  all  its  various  tissues  from  blood  which 
itself  may  be  regarded  as  the  first  completed  tissue.  We  are, 
accordingly,  led  to  inquire  how  this  river  of  life  is  distributed ; 
in  a  word,  into  the  nature  of  the  foetal  circulation. 

Festal  Oixeoktion. — The  blood  leaves  the  placenta  by  the  um- 
bilical vein,  reaches  the  inferior  vena  cava,  either  directly  (by 
the  dtuivs  venoatu),  or,  after  first  passing  to  the  liver  (by  the 
veruB  adveJientes,  and  rotuming  by  the  vetue  revehentes),  and 
proceeds,  mingled  with  the  blood  returning  from  the  lower  ex- 
tremities, to  the  right  auricle.  This  blood,  though  far  from 
being  as  arterial  in  character  as  the  blood  after  birth,  is  the 
best  that  reaches  the  heart  or  any  part  of  Uie  organism.  After 
arriving  at  the  right  auricle,  being  dammed  back  by  the  Eus- 
tachian valve,  it  avoids  the  right  ventricle,  and  shoots  on  into 
the  left  auricle,  passing  thence  into  the  left  ventricle,  from 
which  it  is  sent  into  the  aorta,  and  is  then  earned  by  the  great 
trunks  of  this  arch  to  the  head  and  upper  extremities.  The 
blood  returning  from  these  parts  passes  into  the  right  auricle, 
then  to  the  corresponding  ventricle  and  thence  into  the  pul- 
monary artery;  but,  finding  the  branches  of  this  vessel  un- 
opened, it  takes  the  line  of  least  resistance  through  the  ductus 
arteriosus  into  the  aortic  arch  beyond  the  point  where  its  great 
branches  emerge.  It  will  be  seen  that  the  blood  going  to  the 
head  and  upper  parts  of  the  body  is  greatly  more  valuable  as 
nutritive  pabulum  than  the  rest,  especially  in  the  quantity  of 
oxygen  it  contains ;  that  the  blood  of  the  foetus,  at  best,  is  rela- 
tively ill-supplied  with  this  vital  essential ;  and  as  a  result  we 
find  the  upper  (anterior  in  quadrupeds)  parts  of  the  foetus  best 
developed,  and  a  decided  resemblance  between  the  mammalian 
foetus  ftmctionally  and  the  adult  forms  of  reptiles  and  kindred 


rt  of  abstract 
r  in  foetal  life, 
abound  in  an 
»t  well  under- 
bicli  is  pretty 
;y.  We  may 
entiated  cells 
id  it  will  not 
more  do  they 
der  existence ; 
later  months 

the  adult:  it 
1  blood  which 
sue.  We  are, 
s  distributed ; 

ta  by  the  um- 
r  directly  (by 
3  liver  (by  the 
vehenlea),  and 
.  the  lower  ex- 
ugh  far  from 
r  birth,  is  the 
anism.    After 
ik  by  the  Eus- 
shoots  on  into 
entricle,  from 
d  by  the  great 
remities.    The 
>  right  auricle, 
I  into  the  pul- 
his  vessel  un- 
igh  the  d%idns 
ffhere  its  great 
>d  going  to  the 
re  valuable  as 
he  quantity  of 
at  best,  is  rela- 
as  a  result  we 
the  foetus  best 
iie  mammalian 
es  and  kindred 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.   119 

groups  of  the  lower  vertebrates.     But  this  condition  is  well 
enough  adapted  to  the  general  ends  to  be  attained  at  this  pe- 


Pdmemary  Art. 

ForammOtalt. 
EmIaMmVahe. 

BiglU  Amrie.-V«iU.  Opming. . 


IVmoMry  Art. 
Ltfl  Auride. 
...Left  Aurie.-VaU. 
Opmuig. 


BepaHeVtin. 

BramehM  of  th*  /  ••  .^i 
UmbUietd  Vrin,  -  <  ^=- 
to  thi  IAmt. 


DudmVaumu. 


iDttnui  nUu  Arterim. 
no.  laS.  -Dii«TMii  of  the  f  obUI  clrcu]«tk»  (Flint). 


120 


ANIMAL  PHYSIOLOGY. 


rlod — ^the  nourishment  of  structures  on  the  way  to  a  higher 
path  of  progress. 

As  embryonic  maturity  is  being  reached,  preparation  is  made 
for  a  new  form  of  existence ;  so  it  is  found  that  the  Eustachian 
valve  is  less  prominent  and  the  foramen  ovale  smaller. 

Partubition. 

1*^11  the  efforts  that  have  hitherto  been  made  to  determine 
the  exact  cause  of  the  result  of  that  series  of  events  which  make 
up  parturition  have  failed.  This  has  probably  been  owing  to 
an  attempt  at  too  simple  a  solution.  The  fcetus  lies  surrounded 
(protected)  by  fluid  contained  in  the  amniotic  sac.  For  its  expul- 
sion there  is  required,  on  the  one  hand,  a  dilatation  of  the  uter- 
ine opening  (os  uieri),  and,  on  the  other,  a  vis  a  tergo.  The  lat- 
ter is  furnished  by  the  contractions  of  the  uterus  itself,  aided  by 
the  simultaneous  action  of  the  abdominal  muscles.  Through- 
out the  greater  part  of  gestation  the  uterus  experiences  some- 
what rhythmical  contractions,  feeble  as  compared  with  the 
final  ones  which  lead  to  expulsion  of  the  foetus,  but  to  be  regard- 
ed as  of  the  same  character.  With  the  growth  and  functional 
development  of  other  organs,  the  placenta  becomes  of  less  con- 
sequence, and  a  fatty  degeneration  sets  in,  most  marked  at  the 
periphery,  usually  where  it  is  thinnest  and  of  least  uso.  It  does 
not  seem  rational  to  believe  that  the  onset  of  labor  is  referable 
to  any  one  cause,  as  has  been  so  often  taught;  but  rather  that  it 
is  the  final  ipsue  to  a  series  of  processes  long  existing  and  grad- 
ually, though  at  last  rapidly,  reaching  that  climax  which  seems 
like  a  vital  storm.  The  law  of  rhythm  affects  the  nervous  sys- 
tem as  others,  and  upon  this  depends  the  direction  and  co-ordi- 
nation of  those  many  activities  which  make  up  parturition. 
We  have  seen  that  throughout  the  whole  of  foetal  life  changes 
in  one  part  are  accompanied  by  corresponding  changes  in  oth- 
ers ;  and  in  the  final  chapter  of  this  history  it  is  not  to  be  ex- 
pected that  this  connection  should  be  severed,  though  it  is  not 
at  present  possible  to  give  the  evolution  of  this  proioess  with 
any  more  than  a  general  approach  to  probable  correctness. 


Changes  in  thb  Circulation  after  Birth. 

V^hen  the  new-born  mammal  takes  the  first  breath,  effected 
by  the  harmonious  action  of  the  respiratory  muscles,  excited 
to  action  by  stimuli  reaching  them  from  the  nerve-center  (or 


^to  a  higher 

ration  is  made 
le  Eustachian 
laller. 


to  determine 
;s  which  make 
t)een  owing  to 
es  surrounded 

For  its  expul- 
>n  of  the  uter- 
rgo.  The  lat- 
tself ,  aided  by 
es.  Through- 
)riences  some- 
ired  with  the 
t  to  be  regard- 
nd  functional 
es  of  less  con- 
marked  at  the 
t  uso.  It  does 
or  is  referable 
<  rather  that  it 
ting  and  grad- 
X  which  seems 
e  nervous  sys- 
>n  and  co-ordi- 
p  parturition, 
al  life  changes 
iianges  in  oth- 
9  not  to  be  ez- 
lough  it  is  not 
I  process  with 
irrectness. 

Birth. 

>reath,  effected 
uscles,  excited 
erve-center  (or 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.      121 

centers)  which  preside  over  respiration,  owing  to  its  being 
roused  into  action  by  the  lack  of  its  accustomed  supply  of 
oxygen,  the  hitherto  solid  lungs  are  expanded ;  the  pulmonary 
vessels  are  rendered  permeable,  hence  the  blood  now  takes  the 
path  of  least  resistance  along  them,  as  it  formerly  did  through 
the  ductus  arteriosus.  The  latter,  from  lack  of  uso,  atrophies 
in  most  instances.  The  blood,  returning  to  the  left  auricle  of 
the  heart  from  the  lungs  in  increased  volume,  so  raises  the 
pressure  in  this  chamber  that  the  stream  that  formerly  flowed 
through  the  foramen  ovale  from  the  right  auricle  is  opposed 
by  a  force  equal  to  its  own,  if  not  greater,  and  hence  passes  by 
an  easier  route  into  the  right  ventricle.  The  fold  that  tends  to 
close  the  foramen  ovale  grows  gradually  over  the  latter,  so  that 
it  usually  ceases  to  exist  in  a  few  days  after  birth. 

At  birth,  ligature  of  the  umbilical  cord  cuts  off  the  placental 
circulation ;  hence  the  ductus  venosus  atrophies  and  becomes  a 
mere  li{;ament. 

The  placenta,  being  now  a  foreign  body  in  the  uterus,  is  ex- 
pelled, and  this  organ,  by  the  contractions  of  its  walls,  closes  the 
ruptured  and  gaping  vessels,  thus  providing  against  heemor- 
rhage. 

Coitus  between  the  Sexes. 

In  all  the  higher  vertebrates  congress  of  the  sexes  is  essential 
to  bring  the  male  sexual  product  into  contact  with  the  ovum. 


Fio.  UB.— SeoUon  of  erectUe  tiMue  (Oftdtat).    a,  tnOwoute  of  aonnQoUve  ttame,  with  elastic 
flban,  wMl  bandlM  of  ptain  miuaular  tiMue  (o) ;  b,  TWiovajipacM  (Sohlfw). 


I 


122 


ANIMAL  PHYSIOLOGY. 


Ereciion  of  the  penis  results  from  the  conveyance  of  an 
excess  of  blood  to  the  organ,  owing  to  dilation  of  its  arteries, 
and  the  retention  of  this  blood  within  its  caverns. 

The  structure  of  the  penis  is  peculiar,  and,  for  the  details  of 
the  anatomy  of  both  the  male  and  female  generative  organs, 
the  student  is  referred  to  works  on  this  subject ;  suffice  it  to 
say  that  it  consists  of  erectile  tissue,  the  chief  cha  racteristic  of 
which  is  the  opening  of  the  capillaries  into  cavernous  venous 
spaces  {sinuses)  from  which  the  veinlets  arise ;  with  such  an 
arrangment  the  circulation  must  be  very  slow— the  inflow 
being  greatly  in  excess  df  the  outflow— apart  altogether  from 
the  compressive  action  of  certain  muscles  connected  with  the 
organ.  As  previously  explained,  the  spermatozoa  originate  in 
the  seminal  tubes,  from  which  they  find  their  way  to  the 


no  M0.-8ection  of  pMla  of  three  leiiiliilfaroae  tulHike  of  the  nt  (Bdiafer).  a,  wMi  Oie 
■iSroSoSStoMt  aSTwoed  in  de*«lopromt ;  6,  mow  adranoed :  c,  M«S!»5Jtf^J«: 
TSopedqpennittawMt.  Between  the  tubulea  are  aeen  strand*  of  Intentitiat  cells,  with 
Uood-veasele  and  lymphnqiaoee. 

seminal  vesicles  or  receptacles  for  semen  till  required  to  be 
discharged.  The  spermatozoa  as  they  mature  are  forced  on  by 
fresh  additions  from  behind  and  by  the  action  of  the  ciliated 
cells  of  the  epididymis,  together  with  the  wave-like  (peristaltic) 
action  of  the  vas  deferens.  Discharge  of  semen  during  coitus 
is  effected  by  more  vigorous  peristaltic  action  of  the  vas  defer- 
ens and  the  seminal  vesicles,  followed  by  a  similar  rhythmical 
action  of  the  bulbo-cavernosus  and  ischio-cavernosus  muscles, 
by  which  the  fluid  is  forcibly  ejaculated. 

Semen  itself,  though  composed  essentially  of  spermatozoa, 


atitti 


■mmiwiraiUlMitwifn 


mn 


yance  of  an 
f  its  arteries, 

bhe  details  of 
itive  organs, 
;  suffice  it  to 
racteristic  of 
pnous  venous 
nth  such  an 
— ^the  inflow 
ogether  from 
;ted  with  the 
i  originate  in 
way  to  the 


hlter).  a,  with  the 
oMitalnlng  fully  de- 
teratitiiacells,  with 


squired  to  be 
)  forced  on  by 
yt  the  ciliated 
le  (peristaltic) 
during  coitus 
the  vas  defer- 
ar  rhythmical 
Losus  muscles, 

spermatozoa, 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.      123 

is  mixed  with  the  secretions  of  the  vas  deferens,  of  the  seminal 
vesicles,  of  Cowper's  glands,  and  of  the  prostate.  Chemically 
it  is  neutral  or  alkaline  in  reaction,  highly  albuminous,  and 
contains  nuclein,  lecithen,  cholesterin,  fats,  and  salts. 

The  movements  of  the  male  cell,  owing  to  the  action  of  the 
tail  (ciliiim),  suffice  of  themselves  to  convey  them  to  the  ovi- 


.  n.-Lett  broad  Ugmment,  TiUlojitan  tube,  ovary,  and  pMwariuin  to  tte  ^fo^'^^ 
■  enle).  u,  utonUTT  teUuiiwi  ofiviJlopUm  tube ;  a,  ampuU* ;  /,  flmbrtoted  end  of  th^ 
uoe,  with  the  parovarium  to  Ita  right ;  o,  ovary ;  o.  I,  ovarian  Ui^unent. 

ducts ;  but  there  is  little  doubt  that  during  or  after  sexual  con- 
gress there  is  in  the  female,  even  in  the  human  subject,  at  least 


Fio.  14B.— Oterut  and  ovariea  of  the  low,  wmi-dlaffiaminatio  (after  Dalton).   o,  ovary ;  H, 
Fkllopian  tube ;  h,  horn  of  the  utwua ;  b,  body  6f  the  ulenis ;  ti,  vactoa. 

in  many  cases,  a  retrograde  peristalsis  of  the  uterus  and  ovi- 
ducts which  would  tend  to  overcome  the  results  of  the  activity 


f»(f)esmmmi>!!''iit 


124 


ANIMAL  PHYSIOLOGY. 


of  the  ciliated  cells  lining  the  oviduct.  It  is  known  that  the 
male  cell  can  survive  in  the  female  prgans  of  generation  for 
several  days,  a  fact  not  difficult  to  understand,  from  the  method 
of  nutrition  of  the  female  cell  (ovum) ;  for  we  may  suppose 
that  both  elements  are  not  a  little  alike,  as  they  are  both 
slightly  modified  amoeboid  organisms. 

Herroiu  Xeehaaiim. — Incidental  reference  has  been  made  to 
the  directing  influence  of  the  nervous  system  over  the  events 
of  reproduction ;  especially  their  subordination  one  to  another 
to  bring  about  the  general  result.  These  may  now  be  consid- 
ered in  greater  detail. 

Most  of  the  processes  in  which  the  nervous  system  takes 
part  are  of  the  nature  of  reflexes,  or  tiie  result  of  the  automa- 
ticity  (independent  action)  of  the  nerve-centers,  increased  by 
some  afferent  (ingoing)  impressions  along  a  nerve-path.  It  is 
not  always  possible  to  estimate  the  exact  share  each  factor 
takes,  which  must  be  highly  variable.  Certain  experiments 
have  assisted  in  making  the  matter  clear.  It  has  been  found 
that,  if  in  a  female  dog,  the  spinal  cord  be  divided  when  the 
animal  is  still  a  puppy,  menstruation  and  impregnation  may 
occur.  If  the  same  experiment  be  performed  on  a  male  dog, 
erection  of  the  penis  and  ejaculation  of  semen  may  be  caused 
by  stimulation  of  the  penis.  As  the  section  of  the  cord  has  left 
the  hinder  part  of  the  animal's  body  severed  from  the  brain, 
the  creature  is,  of  course,  unconscious  of  anything  happening 
In  all  the  parts  below  the  section,  of  whatever  nature.  If  the 
nervi  erigentes  (from  the  lower  part  of  the  spinal  cord)  be 
stimulated,  the  penis  is  erected  i  and  if  they  be  cut,  this  act  be- 
comes impossible,  either  reflexly  by  experiment  or  otherwise. 
Seminal  emissions,  it  is  well  known,  may  occur  during  sleep, 
and  may  be  associated,  either  as  result  or  cause,  with  voluptu- 
ous dreams.  OPutting  all  these  facts  together,  it  seems  reason- 
able to  conclude  that  the  lower  part  of  the  spinal  cord  contains 
the  nervous  machinery  requisite  to  initiate  those  influences  (im- 
pulses) which,  passing  along  the  nerves  to  the  generative  or- 
gans, excite  and  regulate  the  j^rocesses  which  take  place  in 
them.  In  these,  vascular  changes,  as  we  have  seen,  always 
play  a  prominent  part. 

Usually  we  can  recognize  some  afferent  influence,  either 
from  the  brain  (psychical),  from  the  surface — at  all  events 
from  without  that  part  of  the  nervous  system  (center)  which 
functions  directly  in  the  various  sexual  processes.  It  is  com- 
mon to  speak  of  a  number  of  sexual  centers — as  the  erection 


THE  DEVELOPMENT  OP  THE  UROGENITAL  SYSTEM.      125 


3wn  that  the 
eneration  for 
n  the  method 
may  suppose 
ley  are  both 

been  made  to 
er  the  events 
le  to  another 
ow  be  consid- 

system  takes 
'  the  automa- 
increased  by 
e-path.  It  is 
3  each  factor 
.  experiments 
us  been  found 
ied  when  the 
ignation  may 
1  a  male  dog. 
Lay  be  caused 
)  cord  has  left 
)m  the  brain, 
ig  happening 
iture.  If  the 
inal  cord)  be 
it,  this  act  be- 
or  otherwise. 

during  sleep, 
with  voluptu- 
seems  reason- 
cord  contains 
njBuences  (im- 
y^nerative  or- 
take  place  in 

seen,  always 

luence,  either 
-at  all  events 
center)  which 
)s.  It  is  com- 
is  the  erection 


center,  the  ejaculatory  center,  etc. — ^but  we  much  doubt  whether 
there  is  such  sharp  division  of  physiological  labor  as  these 
terms  imply,  and  they  are  liable  to  lead  to  misconception ;  ac- 
cordingly, in  the  present  state  of  our  knowledge,  we  prefer  to 
speak  of  the  sexual  center,  using  even  that  term  in  a  somewhat 
broad  sense. 

^he  effects  of  stimulation  of  the  sexual  organs  are  not  con- 
fined to  the  parts  themselves,  but  the  ingoing  impulses  set  up 
radiating  outgoing  ones,  which*  affect  widely  remote  areas  of 
the  body,  as  is  evident,  especially  in  the  vascular  changes ;  the 
central  current  of  nerve  influence  breaks  up  into  many  streams 
as  a  result  of  the  rapid  and  extensive  rise  of  the  outflowing 
current,  which  breaks  over  ordinary  barriers,  and  takes  paths 
which  are  not  properly  its  own.  (Bearing  this  fact  in  mind, 
the  chemical  composition  of  semen,  so  rich  in  proteid  and  other 
material  valuable  from  a  nutritive  point  of  view,  and  consid- 
ering how  the  sexual  appetites  may  engross  the  mind,  it  is  not 
^difficult  to  understand  that  nothing  so  quickly  disorganizes  the^ 
Whole  man,  physical,  mental,  and  moral,  as  sexual  excesses, 
Whether  by  the  use  of  the  organs  in  a  natural  way,  or  from 
/masturbation. 

Qfature  has  protected  the  lower  animals  by  the  strong  bar- 
rier of  instinct,  so  that  habitual  sexual  excess  is  with  them  an 
impossibility,  since  the  females  do  not  permit  of  the  approaches 
of  the  male  except  during  the  rutting  period,  which  occurs  only 
at  stated,  comparatively  distant  periods  in  most  of  the  higher 
mammals,  (^hen  man  keeps  his  sexual  functions  in  subjection 
to  his  higher  nature,  they  likewise  tend  to  advance  his  whole 
development. 

Sammury. — Certain  changes,  commencing  with  the  ripening 
of  ova,  followed  by  their  discharge  and  conveyance  into  the 
uterus,  accompanied  by  simultaneous  and  subsequent  modifica- 
tions of  the  uterine  mucous  membrane,  constitute,  when  preg- 
nancy occurs,  an  unbroken  chain  of  biological  events,  though 
usually  described  separately  for  the  sake  of  convenience. 
When  impregnation  does  not  result,  there  is  a  retrogression  in 
the  uterus  (menstruation)  and  a  return  to  general  quiescence 
in  all  the  reproductive  organs. 

[Parturition  is  to  be  regarded  as  the  climax  of  a  variety  of 
rhythmic  occurrences  which  have  been  gradually  gathering 
head  for  a  long  period.  The  changes  which  take  place  in  the 
placenta  of  a  degenerative  character  fit  it  for  being  cast  off,  and 
may  render  this  structure  to  some  extent  a  foreign  body  before 


' 


^^-I^■rig;.■-:iJh■■^-l-■>M**^^L--■^fe4«^■i^ta!il^^^-S^^?gn^ji4^-■ 


126 


ANIMAL  PHYSIOLOGY. 


it  and  the  foetus  are  finally  expelled,  so  that  these  changes  may 
constitute  one  of  a  number  of  exciting  causes  of  the  increased 
uterine  action  of  parturition.  But  it  is  important  to  regard  the 
whole  of  the  occurrences  of  pregnancy  as  a  connected  series  of 
processes  co-ordinated  by  the  central  nervous  system  so  as  to 
accomplish  one  great  end,  the  development  of  a  new  individual. 

The  nutrition  T)f  the  ovum  in  its  earliest  stages  is  effected  by 
means  in  harmony  with  its  nature  as  an  amoeboid  organism ; 
nutrition  by  the  cells  of  blood-vessels  is  similar,  while  that  by 
villi  may  be  compared  to  what  takes  place  through  the  agency  ^ 
of  similar  structures  in  the  alimentary  canal  of  the  adult  mam- 
mal. 

The  circulation  of  the  foetus  puts  it  on  a  par  physiologically 
with  the  lower  vertebrates.  Before  birth  there  is  a  gradual 
though  somewhat  rapid  preparation,  resulting  in  changes 
which  speedily  culminate  after  birth  on  the  establishment  of 
the  permanent  condition  of  the  circulation  of  extra-uterine  life. 

The  blood  of  the  foetus  (as  in  the  adult)  is  the  great  store- 
house of  nutriment  and  the  common  receptacle  of  all  waste 
products ;  these  lat  ier  are  in  the  main  transferred  to  the  moth- 
er's blood  indirectly  in  the  placenta ;  in  a  similar  way  nutri- 
ment is  imported  from  the  mother's  blood  to  that  of  the  foetus. 
The  placenta  takes  the  place  of  digestive,  respiratory,  and  ex- 
cretory organs. 

{Coitus  is  essential  to  bring  the  male  and  female  elements 
together  in  the  higher  vertebrates.  The  erection  of  the  penis  is 
owing  to  vascular  changes  taking  place  in  an  organ  composed 
of  erectile  tissue ;  ejaculation  of  semen  is  the  result  of  the  peri- 
staltic action  of  the  various  parts  of  the  sexual;  tract,  aided  by 
rhythmical  action  of  certain  striped  muscles.  The  spermatozoa, 
which  are  unicellular,  flagellated  (ciliated)  cells,  make  up  the  es- 
sential part  of  semen ;  though  the  latter  is  complicated  by  tho 
addition  of  the  secretions  of  several  glands  in  connection  with 
the  seminal  tract.  Though  competent  by  their  own  movements 
of  reaching  the  ovum  in  the  oviduct,  it  is  probable  that  the 
uterus  and  oviduct  experience  peristaltic  actions  in  a  direction 
toward  the  ovary,  at  least  in  a  number  of  mammals. 

^he  lower  part  of  the  spinal  cord  is  the  seat  in  the  higher 
mammals  of  a  sexual  center  or  collection  of  cells  that  receives 
afferent  impulses  and  sends  out  efferent  impulses  to  *1"»  sexual 
organs.  Itliis,  like  all  the  lower  centers,  is  under  the  itrol  of 
the  higheir  centers  in  the  brain,  so  that  its  action  may  be  either 
initiated  or  inhibited  by  the  cerebrum. 


changes  may 
the  increased 
to  regard  the 
cted  series  of 
stem  so  as  to 
iw  individual, 
is  effected  by 
id  organism; 
while  that  by 
h  the  agency 
le  adult  mam- 

lysiologically 
is  a  gradual 
:  in  changes 
ablishment  of 
a-uterine  life. 
9  great  store- 
)  of  all  waste 
I  to  the  moth- 
ar  way  nutri- 
of  the  foetus, 
fttory,  and  ex- 
male  elements 
of  the  penis  is 
gan  composed 
lit  of  the  peri- 
ract,  aided  by 
)  spermatozoa, 
ake  up  the  es- 
licated  by  the 
nnection  with 
m  movements 
>able  that  the 
in  a  direction 
Ells. 

in  the  higher 
that  receives 
I  to  *1"»  sexual 
the  itrol  of 
may  be  either 


ORGANIC  EVOLUTION  RECONSIDERED.  127 


OROANIC  EVOLUTION  RECJONSIDERED. 

The  study  of  reproduction  has  prepared  the  student  for  the 
comprehension  of  certain  views  of  the  origin  of  the  forms  of 
life  which  could  not  be  as  profitably  considered  before. 

While  the  great  majority  of  biologists  are  convinced  that 
there  has  been  a  gradual  evolution  of  more  complex  organisms 
from  simpler  ones,  and  while  most  believe  that  Darwin's  the- 
ory furnishes  some  of  the  elements  of  a  solution  of  the  problem 
as  to  how  this  has  occurred,  many  still  feel  that  the  whole  ex- 
planation was  not  furnished  by  that  great  naturalist. 

Accordingly,  we  shall  notice  very  briefly  a  few  of  the  more 
important  contributions  to  this  subject  .rr^ce  Darwin's  views 
were  published. 

In  America,  under  the  influence  of  the  writings  of  Cope  and 
Hyatt,  a  school  of  evolutionists  has  been  formed,  holding  doc- 
trines that  constitute  a  modification  of  those  announced  in 
cruder  form  by  Lamarck,  hence  termed  neo-Lamarckianism. 
These  authors  have  imported  consciousness  into  the  list  of 
factors  of  organic  evolution  and  given  it  a  prominent  place. 
They  regard  consciousness  as  a  fundamental  property  of  proto- 
plasm ;  it  determines  effort  and  the  direction  that  activity  shall 
take :  thus  hunger  leads  to  migration,  and  brings  the  creature 
under  a  new  set  of  conditions  which  influence  its  nature.  A 
certain  proportion  of  the  changes  an  animal  undergoes  are  at- 
tributed to  the  direct  influence  of  surrounding  conditions  (en- 
vironment), but  the  larger  number  are  owing  to  efforts  involv- 
ing the  greater  use  of  some  parts  than  others,  which  tends  to 
become  habitual.  This  is  the  explanation  neo-Liamarckianism 
offers  for  the  origin  of  variations.  It  is  assumed  that  the  re- 
sults of  use  or  disuse  of  parts  is  inherited,  so  that  the  gain  or 
loss  is  not  transient  with  the  individual,  but  remains  with  the 
group. 

This  theory  also  refers  the  loss  or  preservation  of  certain 
s*;ructures  to  "  acceleration  "  or  "  retardation  "  of  growth ;  thus, 
ii  the  growth  of  gills  were  greatly  and  progressively  retarded 
during  embryonic  life,  they  might  become  only  rudimentary, 
and  this  would  furnish  an  explanation  of  the  origin  of  rudiment- 
ary organs,  though  it  is  clear  that  use  and  effort  could  not  di- 
rectly explain  such  acceleration  or  retardation.  It  is  further  a 
fact,  which  this  theory  does  not  explain,  that  all  variations  of 
structure  produced  by  use  are  not  inherited. 


'TJ'^.RRVa^-.^ 


-•Eja^^^ett  jj^^-j^Mg^li^iW^i^te^^ : 


128 


ANIMAL  PHYSIOLOGY. 


\Weismann,  in  fact,  denies  that  peculiarities  acquired  dur- 
ing the  lifetime  of  the  adult  are  passed  on  to  offspring.  This 
writer  believes  that  we  must  seek  in  Amceba,  as  the  ancestral 
representative  of  the  ovum,  for  the  clew  to  the  laws  of  heredity. 
The  Amoeba  must  divide  or  cease  to  exist  as  a  group  form — 
hence  the  segmentation  of  the  ovum ;  this  is  but  the  inherited 
tendency  to  divide.  What  the  individual  becomes  is  determined 
entirely  by  the  ovum,  the  whole  of  which  does  not  develop  into 
the  new  being,  but  a  part  is  laid  aside  in  reserve  as  the  future 
ovum.  Any  variations  that  show  themselves  in  future  indi- 
viduals are  such  as  arise  from  the  variations  of  the  ovum  itself. 
According  to  this  writer,  it  is  as  natural  for  the  offspring  to 
resemble  the  parent  (heredity)  in  the  higher  groups  of  animals 
as  that  one  Amoeba  shouii  resemble  another,  and.  for  the  same 


reason. 


Weismann  has  also  attempted  to  explain  the  necessity  and 
the  significance  of  the  extrusion  of  polar  globules.  The  first 
polar  globule  is  expelled  from  all  ova,  even  those  that  -can  de- 
velop independent  of  a  male  cell  (parthenogenetic).  This  rep- 
resents that  part  of  the  original  ovum  which  determines  its 
peculiarities  of  form,  etc.  (ovogenetic  idioplasm);  while  the 
second  polar  globule  is  one  half  of  the  nucleus  of  the  mature 
ovum  ready  to  enter  upon  development,  if  fertilized.  When 
the  latter  takes  place,  it  is  joined  by  the  corresponding  nuclear 
substance  of  the  male  cell  to  form  the  segmentation  nucleus. 
It  is  this  substance  (germ-plasma)  which  determines  exactly 
what  line  of  development,  to  the  minutest  details,  the  ovum 
shall  follow.  In  the  course  of  time  the  nucleus  would  thus 
come  to  represent  many  generations  of  united  plasmas.  There 
must  be  a  limit  to  this,  from  the  physical  necessities  of  the  case ; 
hence  the  expulsion  of  a  second  polar  globule,  which  also  is  a 
provision  against  parthenogenesis,  for  in  some  cases  the  plasma 
of  the  nucleus  has  the  power,  without  the  accession  of  any 
male  plasma,  to  segment  and  develop  the  mature  animal.  But 
in  any  case  there  is  a  great  advantage  in  the  union  of  the  two 
plasmas  with  their  diverse  experiences;  hence  sexual  repro- 
duction, though  the  most  costly  apparently,  is  in  reality  the 
most  economical  for  Nature  in  the  end,  for  higher  results  are 
reached,  and  it  seems,  in  fact,  that  this  lies  at  the  very  foun- 
dation of  organic  progress. 

The  theory  of  Brooks  may  be  regarded  as  eclectic,  being  a 
combination  of  that  of  WeiSmann  and  Darwin  more  particu- 
larly, with  entirely  new  additions  by  himself. 


titmmf>rvniitif:- 


icquired  dur- 
spring.  This 
the  ancestral 
8  of  heredity, 
^roup  form — 
the  inherited 
is  determined 
;  develop  into 
as  the  future 
.  future  indi- 
e  ovum  itself. 
6  offspring  to 
ps  of  animals 
.  for  the  same 

necessity  and 
es.  The  first 
that  can  de- 
c).  This  rep- 
letermines  its 
[);  while  the 
)f  the  mature 
lized.  When 
nding  nuclear 
ttion  nucleas. 
mines  exactly 
ils,  the  ovum 
IS  would  thus 
bsmas.  There 
es  of  the  case ; 
hich  also  is  a 
>es  the  plasma 
sssion  of  any 
animal.  But 
on  of  the  two 
sexual  repro- 
in  reality  the 
ler  results  are 
he  very  f  oun- 

lectic,  being  a 
more  particu- 


OROANIC  EVOLQTIUN  BECONSIDERED. 


129 


(hs^Twin  believed  that  every  part  of  the  body  gave  off  "  gem- 
mules,"  or  very  minute  bodies,  which  were  collected  into  the 
ovum,  and  thus  the  ovum  came  to  be  a  sort  of  abstract  of  the 
whole  body — hence  the  resemblance  of  offspring  to  parents, 
since  the  development  of  the  ovum  was  but  that  of  the  gem- 
mules.  Some  of  the  gemmules  might  remain  latent  for  genera- 
tions, and  then  develop ;  hence  that  resemblance  often  seen  to 
ancestors  more  remote  than  the  parents  (reversion).  This  is  a 
very  brief  account  of  Darwin's  hypothesis  of  pangenesis. 

This  writer,  however,  never  accounted  for  variations.    He 
spoke  of  variations  as  "  spontaneous,"  meaning,  not  that  they 
were  supernatural,  but  that  it  was  not  possible  to  assign  them 
to  a  definite  cause.    To  account  for  variation  has  naturally  been 
the  aim  of  later  writers.    How  neo-Lamarckianism  does  this 
has  been  already  considered.    We  now  give  the  views  of  Brooks 
on  this  and  other  points  in  connection  with  organic  evolution. 
(This  thinker,  like  Weismann,  looks  to  the  fertilized  ovum 
for  an  explanation  of  the  main  facts ;  but  Brooks  refers  the 
origin  of  variations  to  the  influence  of  the  male  cell.    This  is, 
of  course,  a  pure  hypothesis,  but  it  is  in  harmony  with  many 
facts  which  were  in  need  of  explanation.    It  had  been  noticed 
by  Darwin  that  variations  of  all  kinds  were  most  apt  to  arise 
upon  alteration  in  the  conditions  under  which  an  animal 
lived.    Brooks  also  believes  in  gemmules,  but  does  not  think 
they  are  given  off  from  all  parts  equally  or  at  all  times,  but 
that  they  are  derived  from  those  parts  most  affected  by  the 
change  of  surroundings ;  and  since  this  would  influence  parts 
much  when  for  the  worse,  variation  would  coincide  with  suf- 
fering or  need ;  hence  those  very  parts  would  vary,  and  so  pre- 
pare for  adaptation,  just  when  this  was  most  called  for  by  the 
nature  of  the  case.    But  the  male  sexual  <ilement,  it  has  been 
shown,  is  more  liable  to  variation  than  the  ovum ;  hence  the  ex- 
planation of  what  Brooks  believes  to  be  a  fact,  that  it  is  the 
sperm-cell  that  generally  is  responsible  for  variation,  since  it 
chiefly  collects  the  gemmules. 

(The  author  of  this  theory  points  to  parlhenogenetic  forms 
being  less  variable,  as  evidence  of  the  truth  of  his  view.  To 
introduce  a  male  cell  is  to  impart  vast  numbers  of  new  gem- 
mules, and  thus  induce  variability.  This  hypothesis  would  ex- 
plain why  the  female  represents  what  is  most  fundamental  and 
ancient  in  the  history  of  psychological  development,  and  the 
(  male  what  is  associated  with  enterprise— in  a  word,  the  female 
\  preserves,  the  male  orig^ates,  in  the  widest  sense. 


110 


ANIMAL  PHYSIOLOGY. 


Vines  has  stated  that  the  equivalent  of  parthenogenesis 
takes  place  in  the  male  cell  in  plants.  Though  this  may  be  an 
objection  to  the  universality  of  application  of  Brooks's  theory, 
it  does  not  seem  to  us  to  be  fatal  to  it  as  a  whole. 

As  has  been  pointed  out,  in  a  previous  chapter,  Darwin  held 
that  the  differences  that  caused  ultimately  the  formation  of 
new  groups  of  living  forms  were  the  result  of  extremely  slow 
accumulation  of  variations,  at  first  very  minute.  He  every- 
where insists  upon  this.  But,  unquestionably,  it  is  just  here 
that  the  greatest  difficulty  is  to  be  encountered  in  the  Darwin- 
ian account  of  evolution.  The  chances  against  the  loss  of  the 
variation  by  breeding  with  forms  that  did  not  possess  it  seem 
to  be  numerous,  hence  various  theories  have  been  proposed  to 
lessen  the  difficulty. 

Mivart  introduced  the  doctrine  of  extraordinary  births,  be- 
lieving that  variations  were  often  sudden  and  pronounced. 
That  they  were  so  occasionally  Darwin  himself  admitted ;  but 
he  considered  a  theory  like  that  of  Mivart  as  a  surrender,  a 
resort  to  an  explanation  that  verged  in  its  character  on  the 
introduction  of  the  supernatural  itself. 

(A  view  that  has  attracted  much  attention  and  caused  a 
great  deal  of  controversy,  is  that  of  Romanes,  which  was  intro- 
duced in  part  to  meet  the  difficulty  just  referred  to ;  and  to  lessen 
the  further  one  arising  from  the  infertility  of  species  with  one 
another,  as  compared  with  the  perfect  fertility  of  varieties.  It 
has  often  been  noticed  that,  though  the  difference  anatomically 
between  varieties  might  be  greater  than  between  species,  the 
above  law  as  to  fertility  still  held.  Such  a  fact  calls  for  ex- 
planation ;  hence  Romanes  has  proposed  his  theory  of  "  physi- 
ological selection  "  (segregation,  isolation).  If  it  be  admitted 
that  some  change  may  take  place  in  the  sexual  organs  of  two 
forms  so  that  the  members  of  one  are  fertile  with  each  other 
while  those  of  the  other  are  not,  it  will  at  once  appear  that 
they  are  as  much  isolated  physiologically  as  if  separated  by  an 
ocean.  That  such  does  take  place  is  an  assumption  based  on- 
the  great  tendency  in  the  reproductive  organs  to  change ;  and 
it  is  claimed  that,  if  thi&  assumption  be  granted,  that  the  main 
difficulty  of  Darwin's  theory  will  be  removed,  for  the  "  swamp- 
ing" action  of  intercrossing  forms  that  vary  slightly,  or  one  of 
them  not  at  all,  in  the  given  direction,  will  not  occur.  Romanes 
believes  that  forms  that  vary  are  fertile  inter  se,  but  not  with 
the  parent  forms,  which  would  meet  the  case  fairly  well.  Cer- 
tain it  is  that  iqxioiee  are  not  generally  fertile  with  one  an- 


thenogenesis 
is  may  be  an 
(oks's  theory, 

Darwin  held 
formation  of 
tremely  slow  , 
.  He  every- 
)  is  just  here 
the  Darwin- 
ae  loss  of  the  • 
ssess  it  seem 
L  proposed  to 

ry  births,  be- 
pronounced. 
dmitted;  but 
k  surrender,  a 
racter  on  the 

and  caused  a 
ich  was  intro- 
;  and  to  lessen 
jcies  with  one 
varieties.  It 
anatomically 
n  species,  the 
i  calls  for  ex- 
ry  of  "physi- 
i  be  admitted 
organs  of  two 
ith  each  other 
e  appear  that 
parated  by  an 
>tion  based  on- 
}  change ;  and 
that  the  main 
•the"8wamp- 
htly,  or  one  of 
jur.  Romanes 
!,  but  not  with 
•ly  well.  Cer- 
with  one'an- 


OROANIC  EVOLUTION  RECONSIDERED. 


131 


other  while  varieties  are  so  invariably ;  and  it  is  this  that,  in 
the  opinion  of  Romanes  and  many  others,  has  never  been  ade- 
quately explained. 

Admitting  that  the  tlieories  of  Romanes,  Brooks,  and  Weis- 
mann  have  advanced  us  on  the  way  to  more  complete  views  of 
the  mode  of  origin  of  the  forms  of  the  organic  world,  it  must 
still  be  felt  that  all  theories  yet  propounded  fall  short  of  being 
entirely  satisfactory.  It  seems  to  us  unfortunate  that  the  sub- 
ject has  not  received  more  attention  from  physiologists,  as 
without  doubt  the  final  solution  must  come  through  that  sci- 
ence which  deals  with  the  properties  rather  than  the  forms 
of  protoplasm ;  or,  in  other  words,  the  fundamental  principles 
underlying  organic  evolution  are  physiological.  But,  in  the 
unraveling  of  a  subject  of  such  extreme  complexity,  all  sci- 
ences must  probably  contribute  their  quota  to  make  up  the 
truth,  as  many  rays  of  different  colors  compounded  form  white 
light.  As  with  other  theories  of  the  inductive  sciences,  none 
can  be  more  than  temporary ;  there  must  be  constant  modifi- 
cation to  meet  increasing  knowledge.  Conscious  that  any 
views  we  ourselves  advance  must  sooner  or  later  be  modified 
as  all  others,  even  if  acceptable  now,  we  venture  to  lay  before 
the  reader  the  opinions  we  have  formed  upon  this  subject  as 
the  result  of  considerable  thought. 

All  vital-  phenomena  may  be  regarded  as  the  resultant  of 
the  action  of  external  conditions  and  internal  tendencies.  Amid 
the  constant  change  which  life  involves  we  recognize  two 
things :  the  tendency  to  retain  old  modes  of  behavior,  and  the 
tendency  to  modification  or  variation.  Since  those  impulses 
originally  bestowed  on  matter  when  it  became  living,  must,  in 
order  to  prevail  against  the  forces  from  without,  which  tend 
to  destroy  it,  have  considerable  potency,  the  tendency  to  modi- 
fication is  naturally  and  necessarily  less  than  to  permanence  of 
form  and  function. 

From  these  principles  it  follows  that  wben  an  Amoeba  or 
kindred  organism  divides  after  a  longer  or  shorter  period,  it  is 
not  in  reality  the  same  in  all  respects  as  when  its  existence 
began,  though  we  may  be  quite  unable  to  detect  the  changes ; 
and  when  two  inf usorians  conjugate,  the  one  brings  to  the  other 
protoplasm  different  in  molecular  behavior,  of  necessity,  from 
having  had  different  experiences.  We  attach  great  importance 
to  these  principles,  as  they  seem  to  us  to  lie  at  the  root  of  the 
whole  matter.    What  has  been  said  of  these  lower  but  inde- 


fas*.®-.*** :  '<■ 


% 


132 


ANIMAL  PHYSIOLOGY. 


pendent  forms  of  life  applies  to  the  higher.  All  organisms  are 
made  up  of  cells  or  aggregations  of  cells  and  their  products. 
For  the  present  we  may  disregard  the  latter.  When  a  muscle- 
cell  by  division  gives  rise  to  a  new  cell,  the  latter  is  not  identi- 
cally the  same  iu  every  particular  as  the  parent  cell  was  origi- 
nally. It  is  what  its  parent  has  become  by  virtue  of  those 
experiences  it  has  had  as  a  muscle-cell  per  se,  and  as  a  member 
of  a  populous  biological  community,  of  the  complexities  of 
which  we  can  scarcely  conceive. 

Now,  as  a  body  at  rest  may  remain  so,  or  may  move  in  a 
certain  direction  according  as  the  forces  acting  upon  it  exactly 
counterbalance  one  another,  or  produce  a  resultant  effect  in 
the  direction  in  which  the  body  moves,  so  in  the  case  of  he- 
redity, whether  a  certain  quality  in  the  parent  appears  in  the 
offspring,  depends  on  whether  this  quality  is  neutralized,  aug- 
mented, or  otherwise  modified  by  any  corresponding  quality  in 
the  other  parent,  or  by  some  opposite  quality,  taken  in  connec- 
tion with  the  direct  influence  of  the  environment  during  devel- 
opment. 

This  assumption  explains  among  other  things  why  acquired 
peculiarities  (the  results  of  accident,  habit,  et<;.)  may  or  may 
not  be  inherited. 

These  are  not  usually  inherited  because,  as  is  to  be  expect- 
ed, those  forces  of  the  organism  which  have  been  gathering 
head  for  ages  are  naturally  not  easily  turned  aside.  Again,  we 
urge,  heredity  must  be  more  pronounced  than  variation. 

/The  ovum  and  sperm-cell,  like  all  other  cells  of  the  body, 
are  tnicrocosms  representing  the  whole  to  a  certain  extent  in 
themselves — that  is  to  say,  cell  A  is  what  it  is  by  reason  of  what 
all  the  other  millions  of  its  fellows  in  the  biological  republic 
are ;  so  that  it  is  possible  to  understand  why  sexual  cells  repre- 
sent, embody,  and  repeat  the  whole  biological  story,  though  it 
is  not  yet  possible  to  indicate  exactly  how  they  more  than 
others  have  this  power.  This  falls  under  the  laws  of  speciali- 
zation and  the  physiological  division  of  labor ;  but  along  what 
paths  they  have  reached  this  we  can  not  determine. 

Strong  evidence  is  furnished  for  the  above  views  by  the  his- 
tory of  disease.  Scar-tissue,  for  example,  continues  to  repro- 
duce  itself  as  such ;  like  produces  like,  though  in  this  instance 
the  like  is  in  the  first  instance  a  departure  from  the  normal. 
Gout  is  well  known  to  be  a  hereditary  disease ;  not  only  so,  but 
it  arises  in  the  offspring  at  about  the  same  age  as  in  the  parent, 
which  is  equivalent  to  saying  that  in  the  rhythmical  life  of 


rir.Ty".u~~-yj.xi'Am''Uk'hmi:?s,i-'-*sAK^^^^^ 


ORGANIC  EVOLUTION  RECONSIDERED. 


183 


gamsms  are 
ir  products, 
en  a  muscle- 
8  not  identi- 
)11  was  origi- 
tue  of  those 
as  a  member 
nplexities  of 

move  in  a 
on  it  exactly 
ant  effect  in 
e  case  of  he- 
pears  in  the 
iralized,  aug- 
[ig  quality  in 
an  in  connec- 
luring  devel- 

frhy  acquired 
may  or  may 

to  be  expect- 
len  gathering 
B.  Again,  we 
■iation. 
of  the  body, 
ain  extent  in 
eason  of  what 
fical  republic 
al  cells  repre- 
iry,  though  it 
ly  more  than 
vs  of  speciali- 
it  along  what 
le. 

wa  by  the  his- 
lues  to  repro- 
this  instance 
n  the  normal. 
>t  only  so,  but 
in  the  parent, 
[imical  life  of 


certain  cells  a  period  is  reached  when  they  display  the  behav- 
ior, physiologically,  of  their  parents.  iTet  gout  is  a  disease 
that  can  be  traced  to  peculiar  habits  of  living  and  may  be 
eventually  escaped  by  radical  changes  in  this  respect — that  is 
to  say,  the  behavi«)r  of  the  cells  leading  to  gout  can  be  induced 
and  can  be  altered ;  gout  is  hereditary,  yet  eradicable. 

^  Just  as  gout  may  be  set  up  by  formation  of  certain  modes 
of  action  of  the  cells  of  the  body,  so  may  a  mode  of  behavior,  in 
the  nervous  system,  for  example,  become  organized  or  fixed,  be- 
come a  habit,  and  so  be  transmitted  to  offspring.  It  will  pass 
to  the  descendants  or  not  according  to  the  principles  already 
noticed.  If  so  fixed  in  the  individual  in  which  it  arises  as  to 
predominate  over  more  ancient  methods  of  cell  behavior,  and 
not  neutralized  by  the  strength  of  the  normal  physiological  ac- 
tion of  the  corresponding  parts  in  the  other  parent,  it  will  reap- 
pear. We  can  never  determine  whether  this  is  so  or  not  before- 
hand ;  hence  the  fact  that  it  is  impossible,  es:  eciall.y  in  the  ca.i8 
of  man,  whose  vital  processes  are  so  modified  by  his  p-ychic 
life,  to  predict  whether  acquired  variations  shall  become  heredi- 
tary ;  hence  also  the  irregularity  which  characterizes  h'.redity 
in  such  cases ;  they  may  reappear  in  offspring  or  they  :aay  not. 
In  viewing  heredity  and  modification  it  is  impossible  to  get  b 
true  insight  into  the  matter  without  taking  into  the  accovni 
both  original  natural  tendencies  of  living  matter  an(^  thp  influ- 
ence of  environment.  We  only  know  of  vital  ma- aiV;u  nations 
in  some  environment ;  and,  so  far  as  our  experience  ^oes,  ^ife  is 
impossible  apart  from  the  influence  of  surroundings.  With 
these  general  principles  to  guide  us,  we  shall  attempt  a  brief 
examination  of  the  leading  theories  of  organic  evolution. 

^irst  of  all,  Spencer  seems  to  be  correct  in  regarding  evolu- 
tion as  universal,  and  organic  evolution  but  one  j:Art  of  a 
whole.  No  one  who  looks  at  the  facts  presented  in  every  field 
of  nature  can  doubt  that  struggle  (opposition,  action  and  reac- 
tion) is  universal,  and  that  in  the  organic  world  the  fittest  to  a 
given  environment  survives.  But  Darwin  has  probably  fixed 
his  attention  too  closely  on  this  principle  and  attempted  to  ex- 
plain too  much  by  it,  as  well  as  faik  :  *:r>  see  that  there  are 
other  deeper  facts  underlying  it.  VaTia' .  on,  which  this  author 
scarcely  attempted  to  explain,  seems  to  us  to  be  the  natural  re- 
sult of  the  very  conditions  under  which  living  things  have  an 
existence.  Stable  equilibrium  is  au  idea  incompatible  with  our 
fundamental  conceptions  of  ]if  .  Altered  function  implies  al- 
tered molecular  action,  which  sometimes  leads  to  appreciable 


184 


ANIMAL  PHYSIOLOGY. 


structural  change.  From  our  conceptions  of  the  nature  of  liv- 
ing matter,  it  naturally  follows  that  variation  should  be  great- 
est, as  has  been  observed,  under  the  greatest  alteration  in  the 
surroundings. 

We  are  but  very  imperfectly  acquainted  as  yet  with  the 
conditions  under  which  life  existed  in  the  earlier  epochs  of  the 
earth's  history.  Of  late,  deep-sea  soundings  and  arctic  explo- 
rations have  brought  surprising  facts  to  light,  showing  that 
living  matter  can  exist  under  a  greater  variety  of  conditions 
than  was  previously  supposed.  Thus  it  turns  out  that  light  is 
not  an  essential  for  life  everywhere.  We  think  these  recent 
revelations  of  unexpected  facts  should  make  us  cautious  in  as- 
suming that  life  always  manifested  itself  under  conditions 
closely  similar  to  those  we  know.  Variation  may  at  one  period 
have  been  more  sudden  and  marked  than  Darwin  supposes; 
and  there  does  seem  to  be  room  for  such  a  conception  as  the 
"  extraordinary  births  "  of  Mi vart  implies ;  though  we  would  not 
have  it  understood  that  we  think  Darwin's  view  of  slow  modi- 
fication inadequate  to  produce  a  new  species ;  we  simply  vent- 
ure to  think  that  he  was  not  justified  in  insisting  so  strongly 
that  this  was  the  only  method  of  Nature ;  or,  to  put  it  more 
justly  for  the  great  author  of  the  "  Origin  of  Species,"  with  the 
facts  that  have  accumulated  since  his  time  he  would  scarcely 
be  warranted  in  maintaining  so  rigidily  his  conviction  that 
new  forms  arose  almost  exclusively  by  the  slow  process  he  has 
so  ably  described. 

As  there  must  be  all  degrees  in  consciousness,  we  do  not 
deny  that  it  may  be  logical  to  assume  some  dim  spark  of  this 
quality  in  all  protoplasm,  as  Cope  insists ;  and  that  it  plays  a 
part  in  determining  action  and  growth  there  seems  to  be  no 
doubt.  But  is  it  not  more  philosophical  to  regard  conscious- 
ness and  all  allied  qualities  as  correlatives,  and  uiiderlaid  by  a 
molecular  constitution  with  which  it  is  associated  as  other  qual- 
itiM  ?   Tt  is  unduly  exalted  in  the  neo-Lamarckian  philosophy. 

^Te  jaust  allow  a  great  deal  to  use  and  effort,  doubtless,  and 
they  explain  the  origin  of  variations  up  to  a  certain  point,  but 
the  solution  is  only  partial.  "Variations  must  arise  a^s  we  have 
attempted  to  explain,  and  use  and  disuse  are  only  two  of  the 
factors  amid  many.  Correlated  growth,  or  the  changes  in  one 
part  induced  by  changes  in  another,  is  a  principle  which,  though 
recognized  by  Darwin,  Cope,  and  others,  has  not,  we  think,  re- 
ceived the  attention  it  deserves.  To  the  mind  of  the  physiolo- 
gist, aU  changes  must  be  correlated  with  others. 


THE  CHEMICAL  CONSTITUTION  OF  THE  ANIMAL  BODY.  185 


nature  of  liv- 
3uld  be  great- 
eratiou  in  the 

yet  with,  the 
epochs  of  the 
[  arctic  explo- 
showing  that 
of  conditions 
b  that  light  is 
k  these  recent 
autious  in  as- 
ler  conditions 
^  at  one  period 
sfivL  supposes; 
;eption  as  the 
I  we  would  not 
of  slow  niodi- 
B  simply  vent- 
,g  so  strongly 

0  put  it  more 
cies,"  with  the 
«rould  scarcely 
onviction  that 
process  he  has 

ess,  we  do  not 

1  spark  of  this 
hat  it  plays  a 
leems  to  be  no 
ard  conscious- 
aiiderlaid  by  a 
.  as  other  qual- 
&n  philosophy, 
doubtless,  and 
tain  point,  but 
rise  ais  we  have 
tnly  two  of  the 
ihanges  in  one 
which,  though 
[;,  we  think,  re- 
f  the  physiolo- 


This  principle  has  played  a  great  part  in  the  development  of 
man,  as  we  shall  show  later. 

f Weismann's  theories  have  called  attention  to  the  ovum  in  a 
new  and  valuable  way,  though  he  seems  to  have  given  too  ex- 
clusive attention  to  the  nucleus  {germ-plaama)  in  itself  and 
out  of  relation  to  the  influence  of  the  countless  cells  that 
make  up  the  body  and  must  be  constantly  determining  modi- 
fications of  the  generative  organs  and  the  sexual  cells  them- 
selves ;  so  that  Brooks's  explanation,  by  adding  a  new  factor, 
or,  at  least,  presenting  a  new  aspect  of  the  case,  was  called 
for  and  seems  to  be  warranted  on  the  general  principle  that 
advance  in  protoplasmic  life  is  dependent  on  new  experiences, 
and  that  the  male  cell  represents  a  little  world  of  the  concen- 
trated experidnces  gathered  during  the  lifetime  of  the  or- 
ganism that  produced  it.  But  we  must  consider  the  whole 
doctrine  of  gemmules  as  a  crude  and  entirely  unnecessary 
hypothesis. 

In  what  sense  has  the  line  that  evolution  has  taken  been 
predetermined  ?  In  the  sense  that  all  things  in  the  universe 
are  unstable,  are  undergoing  change,  leading  to  new  forms  and 
qualities  of  such  a  character  that  they  result  in  a  gradual  prog- 
ress toward  what  our  minds  can  not  but  consider  higher  mani- 
festations of  being. 

The  secondary  methods  according  to  which  this  takes  place 
constitute  the  laws  of  nature,  and  as  we  learn  from  the  progress 
of  science  are  very  numerous.  The  unity  of  nature  is  a  real- 
ity toward  which  our  conceptions  are  constantly  leading  us. 
Evolution  is  a  necessity  of  living  matter  (indeed,  all  matter)  as 
we  view  it. 


THE  CHEMICAL  CONSTTTUTION  OP  THE  ANIMAL  BODY. 

(^ne  visiting  the  ruins  of  a  vast  and  elaborate  building, 
which  had  been  thoroughly  pulled  to  pieces,  would  get  an 
amount  of  information  relative  to  the  original  structure  and 
uses  of  the  various  parts  of  the  edifice  largely  in  proportion  to 
his  familiarity  with  architecture  and  the  various  trades  which 
make  *hat  art  a  practical  success.  The  study  of  the  chemistry 
of  the  animal  body  is  illustrated  by  such  a  case.  Any  attempt 
to  determine  the  exact  chemical  composition  of  living  matter 
must  result  in  its  destruction ;  and  the  amount  of  information 
conveyed  by  the  examination  of  the  chemical  ruins,  so  to  speak. 


186 


ANIMAL  PHYSIOLOGY. 


will  depend  a  great  deal  on  the  knowledge  already  possessed  of 
chemical  and  vital  processes. 

(it  is  in  all  probability  true  that  the  nature  of  any  vital  pro- 
cess is  at  all  events  closely  bound  up  with  the  chemical  changes 
involved ;  but  we  must  not  go  too  far  in  this  direction.  We  are 
not  yet  prepared  to  say  that  life  is  only  the  manifestation  of 
certain  chemical  and  physical  processes,  meaning  thereby  such 
chemistry  and  physics  as  are  known  to  us ;  nor  are  we  prepared 
to  go  the  length  of  those  who  regard  life  as  but  the  equivalent 
of  some  other  force  or  forces ;  as  electricity  may  be  considered 
as  the  transformed  representative  of  so  much  heat  and  vice 
versa.  It  may  be  so,  but  we  do  not  consider  that  this  view  is 
warranted  in  the  present  state  of  our  knowledge. 

On  the  other  hand,  vital  phenomena,  when  our  investiga- 
tioiis  are  pushed  fa,r  enough,  always  seem  to  be  closely  asso- 
ciated with  chemical  action ;  hence  the  importance  to  the  stu- 
dent of  physiology  of  a  sound  knowledge  of  chemical  princi- 
ples. We  think  the  most  satisfactory  method  of  studying  the 
functions  of  an  organ  will  be  found  to  be  that  which  takes  into 
consideration  the  totality  of  the  operations  of  which  it  is  the 
seat,  together  with  its  structure  and  chemical  composition; 
hence  we  shall  treat  chemical  details  in  the  chapters  devoted  to 
special  physiology,  and  here  give  only  such  an  outline  as  will 
bring  before  the  view  the  chemical  composition  of  the  body  in 
its  main  outlines ;  and  even  many  of  these  will  gather  a  signifi- 
cance, as  the  study  of  physiology  progresses,  that  they  can  not 
possibly  have  at  the  present. 

(f^Bwer  than  one  third  of  the  chemical  elements  enter  into 
the  composition  of  the  mammalian  body ;  in  fact,  the  great 
bulk  of  the  organism  is  composed  of  carbon,  hydrogen,  nitro- 
gen, and  oxygen;  sodium,  potassium,  magnesium,  calcium, 
sulphur,  phosphorus,  chlorine,  iron,  fluorine,  silicon,  though 
occurring  in  very  small  quantity,  seem  to  be  indispensable  to 
the  living  body ;  while  certain  others  are  evidently  only  pres- 
ent as  foreign  bodies  or  impurities  to  be  thrown  out  sooner 
or  later.  It  need  scarcely  be  said  that  the  elements  do  not 
occur  as  such  in  the  living  body,  but  in  combination  form- 
ing salts,  which  latter  are  usually  united  with  albuminous 
compounds.  As  previously  mentioned,  the  various  parts  which 
make  up  the  entire  body  of  an  animal  are  composed  of  living 
matter  i .  i  very  different  degrees ;  heupe  we  find  in  such  parts 
as  the  bones  abundance  of  salts,  relative  to  the  proportion  of 
proteid  matter ;  a  condition  demanded  by  that  rigidity  without 


J  possessed  of 

iny  vital  pro- 
nical  changes 
tion.  We  are 
.nifestation  of 
thereby  such 
e  we  prepared 
he  equivalent 
be  considered 
[leat  and  vice 
it  this  view  is 

>ur  investiga- 
I  closely  asso- 
se  to  the  stu- 
)mical  princi- 

studying  the 
ich  takes  into 
hich  it  is  the 

composition ; 
ers  devoted  to 
)utline  as  will 
f  the  body  in 
kther  a  signifi- 

they  can  not 

Dts  enter  into 
vit,  the  great 
drogen,  nitro- 
ium,  calcium, 
ilicon,  though 
dispensable  to 
itly  only  pres- 
im  out  sooner 
ments  do  not 
dnaiion  form- 
h  albuminous 
IS  parts  which 
osed  of  living 
in  such  parts 
proportion  of 
gidity  without 


THE  CHEMICAL  CONSTITUTION  OP  THE  ANIMAL  BODY.  137 

which  an  internal  skeleton  would  be  useless,  a  defect  well  illus- 
trated by  that  disease  of  the  bones  known  as  rickets,  in  which 
the  lime-salts  are  insuflPcient.  It  is  manifest  that  there  may  be 
a  very  great  variety  of  classifications  of  the  compounds  found 
in  the  animal  1> -^v  according  as  we  regard  it  from  a  chemical, 
physical,  or  pfcv.s^ological  point  of  view,  or  combine  many 
aspects  in  one  whole.  The  latter  is,  of  course,  the  most  correct 
and  profitable  method,  and  as  such  is  impossible  at  this  stage 
of  the  student's  progress ;  we  shall  simply  present  him  with  the 
following  outline,  which  will  be  found  both  simple  and  com- 
prehensive.* The  subject  of  Animal  Chemistry  will  be  found 
treated  in  detail  in  the  Appendix. 

CHEMICAL  CONSTITUTION  OF  THE  BODY. 

Such  food  as  supplies  energy  directly  must  contain  carbon 
compounds. 

Living  matter  or  protoplasm  always  contains  nitrogenous 
carbon  compounds. 

In  consequence,  C,  H,  O,  N,  are  the  elements  found  in  great- 
est abundance  in  the  body. 

The  elements  S  and  P  are  associated  with  the  nitrogenous 
carbon  compounds ;  they  also  form  metallic  sulphates  and  phos- 
phates. 

CI  and  F  form  salts  with  the  alkaline  metals  Na,  K,  and  the 
earthy  metals  Ca  and  Mg. 

Fe  is  found  in  hamoglobin  and  its  derivatives. 
(^VProtoplasnOjL^wlien  submitted  to  chemical  examination,  is 
killed.    It  Is  then  found  to  consist  of  proteids,  fats,  carbohy- 
drate, salines,  and  extractives. 

It  is  probable  that  when  living  it  has  a  very  complex  mole, 
oule  consisting  of  C,  H,  O,  N,  8,  and  P  chiefly. 


1.  Organic. 


(a)  Nitrogenous. 


PROXIMATE  PRINCIPLES. 

(  Proteids. 

( Certain  crystalline  bodies. 

^  (b)  Non-nitrogenous,  j  -^^   ^      ^ 

^   ,  (  Mineral  salts. 

8.  Inorganic.  ]  ^^^^ 


Salts.— In  general,  the  salts  of  sodium  are  more  characteris- 
tic of  animal  tissues  and  those  of  potassium  of  vegetable  tissues. 


•  Taken  from  the  author's  "  Ootiinesof  Lectures  on  Physiology,"  W.  Drysdalt 
&  Co.,  Montreal. 


%^_P!^,:&tiUUiSSim<U'J^m3^'^S6ki^>.^^^^ 


188 


ANIMAL  PHYSIOLOGY. 


Na  CI  is  more  abundant  in  the  fluids  of  animals ;  K  and 
phosphates  more  abundant  in  the  tiaaues. 

Earthy  salts  are  most  abundant  in  the  harder  tissues. 

The  salts  are  probably  not  much,  if  at  all,  changed  in  their 
passage  through  the  body. 

In  some  cases  there  is  a  change  from  acid  to  neutral  or 
alkaline. 

The  salts  are  essential  to  preserve  the  balance  of  the  nutri- 
tive processes.    Their  absence  leads  to  disease,  e.  g.,  scurvy. 


GENERAL  CHARACTERISTICS  OF  PROTBID8. 

They  are  the  chief  constituents  of  most  living  tissues,  in- 
cluding blood  and  lymph. 

The  molecule  consists  of  a  great  number  of  atoms  (complex 
constitution),  and  is  formed  of  the  elements  C,  H,  N,  O,  S,  and  P. 

All  proteids  are  amorphous. 

All  are  non-diflfusible,  the  peptones  excepted. 

They  are  soluble  in  strong  adds  and  alkalies,  with  change 
of  properties  or  constitution. 

In  general,  they  are  coagulated  by  alcohol,  ether,  and  heating. 

Coagulated  proteids  are  soluble  only  in  strong  acids  and 
alkalies. 

Classification  and  Distinguishing  Characters  of  Proteids. 

1.  Native  albumins :  Serum  albumin ;  egg  albumin ;  soluble 
in  water. 

2.  Derived  albumins  (albuminates) :  Acid  and  alkali  albu- 
min ;  casein ;  soluble  in  dilute  acids  and  alkalies,  insoluble  in 
water.    Not  precipitated  by  boiling. 

3.  Olobvlina:  Globulin  (globin) ;  paraglobulin ;  myosin; 
fibrinogen.  Soluble  in  dilute  saline  solutions,  and  precipitated 
by  stronger  saline  solutions. 

4.  Peptones:  Soluble  in  water;  diffusible  through  animal 
membranes ;  not  precipitated  by  acids,  alkalies,  or  heat.  De- 
rived from  the  digestion  (peptic,  pancreatic)  of  all  proteids. 

6.  Fibrin:  Insoluble  in  water  and  dilute  saline  solutions. 
Soluble,  but  not  readily,  in  strong  saline  solutions  and  in  dilute 
acids  and  alkalies. 

CERTAIN  NON-CRTSTALLINE  BODIES. 

The  following  bodies  are  allied  to  proteids,  but  are  not  the 
equivalents  of  the  latter  in  the  food. 


imals;  E  and 

tissues, 
uged  in  their 

to  neutral  or 

( of  the  nutri- 
g.,  scurvy. 

IDS. 

ng  tissues,  in- 

boms  (complex 
N,  0,8,  and  P. 


},  with  change 

ir,  and  heating. 
3ng  acids  and 


of  Proteids. 
mmin;  soluble 

td  alkali  albu- 
js,  insoluble  in 

ulin;   myosin; 
id  precipitated 

irough  animal 
,  or  heat.    De- 
lU  proteids.    ' 
irline  solutions. 
IS  and  in  dilute 


B. 

but  are  not  the 


THE  CHEMICAL  CONSTITUTION  OP  THE  ANIMAL  BODY.  189 

They  are  all  composed  of  C,  H,  N,  O.  Chondrin,  gelatin, 
ceratin  have,  in  addition,  S. 

Chondrin:  The  organic  basis  of  cartilage.  Its  solutions 
set  into  a  firm  jelly  on  cooling. 

OeMin :  The  organic  basis  of  bone,  teeth,  tendon,  etc.  Its 
solutions  set  (glue)  on  cooling. 

Elastin :  The  basis  of  elastic  tissue.  Its  solutions  do  not  set 
jelly-like  (gelatinize). 

Mticin :  From  the  secretion  of  mucous  membranes ;  precipi- 
tated by  acetic  acid,  and  insoluble  in  excess. 

Keratin :  Derived  from  hair,  nails,  epidermis,  horn,  feathers. 
Highly  insoluble. 

Nuclein:  Derived  from  the  nuclei  of  cells.  Not  digested 
by  pepsin ;  contains  P  but  no  S. 

THE  PATS. 

The  fats  are  hydrocarbons ;  are  less  oxidized  than  the  carbo- 
hydrates; are  inflammable;  possess  latent  energy  in  a  high 
degree. 

Chemically,  the  neutral  fats  are  glycerides  or  ethers  of  the 
fatty  acids,  i.  e.,  the  acid  radicles  of  the  fatty  acids  of  the  oleic 
and  acetic  series  replace  the  exchangeable  atoms  of  H  in  the 
triatomic  alcohol  glycerine,  e.  g. : 

Olycerine.  Pftlmltio  add.  Gljroeriiie  tripcOmltAte  or  palmitin. 

)  OH     HO.OC.CHm  ( O.CO.CH,, 

C.H.  [  OH  +  HO.OC.CH,,  =  C,H,  ]  O.CO.C,.H„  +  3H,0 
)0H     HO.OC.C..H,,  (O.CO.C«H„ 

A  soap  is  formed  by  the  action  of  caustic  alkalies  on 
fats,  e.  g. : 


Tripalmitin, 

C,H, 


FoUnlum  p«lmitate. 


(cS..,h..3,KOH,  =  sj(C"H.O)oJ,Ca.Jo, 

The  soap  may  be  decomposed  by  a  strong  acid  into  a  fatty 
acid  and  glycerine,  e.  g. : 

C,.H„.CO,K  +  HCl  =  0,.H„.CO,H -f- KCl. 

PotaMium  palmltate.  Palmitio  aoid. 

The /ate  are  insoluble  in  water,  but  soluble  in  hot  alcohol, 
ether,  chloroform,  etc. 

The  alkaline  soaps  are  soluble  in  water. 


i*i.'*»«>*WvS 


140 


ANIMAL  PHYSIOLOGY. 


Most  animal  fats  are  mixtures  of  several  kinds  in  varying 
proportion ;  hence  the  melting-point  for  the  fat  of  each  species 
of  animal  is  different. 

PECULIAR  FATS. 

Lecithin,  Protagon,  Cerebrin  : 

They  consist  of  C,  H,  N,  O,  and  the  first  two  of  P  in  addi- 
tion. 

They  occur  in  the  nervous  tissues. 

i 

CARBOHTDRATBS. 

General  formula,  C»  (H,0).. 

1.  The  Sugars:  Dextrose,  or  grape-sugar,  C«HhO«  +  H,0 
readily  undergoes  alcoholic  fermentation;  less  readily  lactic 
fermentation. 

Lactose,  milk-sugar,  C„H  O,,  +  H,0 ;  susceptible  of  the  lactic 
acid  fermentation. 

InosU,  or  muscle-sugar,  C.H„0.  -•-  2H,0;  capable  of  the  lac- 
tic fermentation. 

MaUose,  C„H„0„  +  H.0,  capable  of  the  alcoholic  fermenta- 
tion.   The  chief  sugar  of  the  digestive  process. 

All  the  above  are  much  less  sweet  and  soluble  than  ordinary 
cane-sugar. 

2.  The  Starches:  Glycogen,  C,HwO„  convertible  into  dex- 
trose. Occurs  abundantly  in  many  foetal  tissues  and  in  the 
liver,  especially  of  the  adult  animal. 

Dextrin,  C.H,»0„  convertible  into  dextrose.  Soluble  in 
water;  intermediate  between  starch  and  dextrose;  a  product 

of  digestion.  .     j-  i  < 

Pathologicdl :  Grape-sugar  occurs  in  the  urine  m  duibetes 

mellitViS. 

Certain  substances  formed  within  the  body  may  be  regarded 
as  chiefly  waste-products,  t  ae  result  of  metabolism  or  tissue- 
changes. 

They  are  divisible  into  nitrogenous  metabolites  and  non- 
nitrogenous  metabolites. 

Nitrogenoiia  Metc^dites. 

1.  Urea,  uric  acid  and  compounds,  kreatinin,  xanthin,  hypo- 
xanthin  (sarkin),  hippuric  acid,  all  occurring  in  urine. 

2.  Leucin,  tyrosin,  taurocholio,  and  glycocholic  acids,  which 
occur  in  the  digestive  tract. 


ids  in  vaiTdng 
}f  each  species 


of  P  in  addi- 


C.H„0,  +  H.0 
readily  lactic 

ble  of  the  lactic 

able  of  the  lac- 

lolic  fermenta- 

j  than  ordinary 

rtible  into  dex- 
iies  and  in  the 

e.     Soluble  in 
ose;  a  product 

ine  in  dic^etea 


[lay  be  regarded 
>lism  or  tissue- 

olites  and  non- 


,  xanthin,  hypo- 

L  urine. 

)lic  acids,  which 


PHYSIOLOGICAL  RESEARCH,  PHYSIOLOGICAL  REASONING.  141 

3.  Kreatin,  constantly  found  in  muscle,  and  a  few  others  of 
less  constant  occurrence. 

The  above  consists  of  C,  H,  N,  O.  Taurocholic  acid  contains 
also  S. 

The  molecule  in  most  instances  is  complex. 

Non-Nitrogenous  Metabolites. 

These  occur  in  small  quantity,  and  some  of  them  are  secreted 
in  an  altered  form. 

They  include  lactic  and  sarcolactic  acid,  oxalic  acid,  succinic 
acid,  etc. 


PHYSIOLOGICAL  RESEARCH  AND  PHYSIOLOGICAL 
REASONING. 

We  propose  in  this  chapter  to  examine  into  the  methods 
employed  in  physiological  investigation  and  teaching,  and  the 
character  of  conclusions  arrived  at  by  physiologists  as  depend- 
ent on  a  certain  method  of  reasoning. 

[The  first  step  toward  a  legitimate  conclusion  in  any  one  of 
Hie  inductive  sciences  to  which  physiology  belongs  is  the  col- 
lection of  facts  which  are  to  constitute  the  foundation  on 
which  the  inference  is  to  be  based.  If  there  be  any  error  in 
these,  a  correct  conclusion  can  not  be  drawn  by  any  reliable 
logical  process.  On  the  other  hand,  facts  may  abound  in  thou- 
sands and  yet  the  correct  conclusion  never  be  reached,  because 
the  method  of  interpretation  is  faulty,  which  is  equivalent  to 
saying  that  the  process  of  inference  is  either  incomplete  or  in- 
coirect.  The  conclusions  of  the  ancients  in  regard  to  nature) 
were  usually  faulty  from  errors  in  both  these  directions;  theys 
neither  had  the  requisite  facts,  nor  did  they  correctly  interpret 
those  with  which  they  were  conversant. 

(Let  us  first  examine  into  the  methods  employed  by  modem 
physiologists,  and  determine  in  how  far  they  jure  reliable.  First, 
there  is  the  method  of  direct  observation,  in  which  no  appara- 
tus whatever  or  only  the  simplest  kind  is  employed ;  thus,  the 
student  may  count  his  own  respirations,  feel  his  own  heart- 
beats, count  his  pulse,  and  do  a  very  great  deal  more  that  will 
be  pointed  out  hereafter ;  or  he  may  examine  in  like  manner  an- 
other fellow-being  or  one  of  the  lower  animals.  This  method 
is  simple,  easy  of  application,  and  is  that  usually  employed  by 
the  physician  even  at  the  present  day,  especially  in  private 


149 


ANIMAL  PHYSIOLOOr. 


practice.  The  value  of  the  results  ohviously  depends  on  the 
reliability  of  the  observer  in  two  respects :  First,  as  to  the  ac- 
curacy, extent,  and  delicacy  of  his  i)erceptions ;  and,  secondly, 
on  the  inferences  based  on  these  sense-observations.  Much 
must  depend  on  practice — ^that  is  to  say,  the  education  of  the 
senses.  The  hand  may  become  a  most  delicate  instrument  of 
observation ;  the  eye  may  learn  to  see  what  it  once  could  not ; 
the  ear  to  detect  and  discriminate  what  is  quite  beyond  the 
uncultured  hearing  of  the  many.  But  it  is  one  of  the  most 
convincing  evidences  of  man's  superiority  that  in  every 
field  of  observation  he  has  risen  above  the  lower  animals,, 
some  of  which  by  their  unaided  senses  naturally  excel  him. 
So  in  this  science,  instruments  have  opened  up  mines  of  facts 
that  must  have  otherwise  remained  hidden;  they  have,  as 
it  were,  provided  man  with  additional  senses,  so  much  have 
the  natural  powers  of  those  he  already  possessed  been  sharp- 
ened. 

HBut  the  chief  value  of  the  results  reached  by  instruments 
consists  in  the  fact  that  the  movements  of  the  living  body  can 
be  registered  ;  i.  e.,  the  great  characteristic  of  modem  physiol- 
ogy is  the  extensive  employment  of  the  graphic  method,  which 
has  been  most  largely  developed  by  the  distinguished  French 
experimenter  Marey.  Usually  the  movements  of  the  point  of 
lever  are  impre^ed  on  a  smoked  surface,  either  of  glazed 
paper  or  glass,  and  rendered  permanent  by  a  coating  of  some 
material  applied  in  solution  and  drying  quickly,  as  shellac  in 
alcohol.  The  surface  on  which  the  tracing  is  written  may  be 
stationary,  though  this  is  rarely  the  case,  as  the  object  is  to  get 
a  succession  of  records  for  comparison ;  hence  the  most  used 
form  of  writing  surface  is  a  cylinder  which  may  be  raised  or 
lowered,  and  which  is  moved  around  regularly  by  some  sort  of 
clock-work.  It  follows  that  the  lever-point,  which  is  moved  by 
the  physiological  effect,  describes  cur»^es  of  varying  complexity. 
That  tracings  of  this  or  any  other  character  should  be  of  any 
value  for  the  purposes  of  physiology,  they  must  be  susceptible 
of  relative  measurement  both  for  time  and  space.  This  can  be 
accomplished  only  when  there  is  a  known  base-line  or  abscissa 
from  which  the  lever  begins  its  rise,  and  a  time  record  which  is 
usually  in  seconds  or  portions  of  a  second.  The  first  is  easily 
obtained  by  simply  allowing  the  lever  to  write  a  straight  line 
before  the  physiological  effect  proper  is  recorded.  Time  inter- 
vals are  usually  indicated  by  the  interruptions  of  an  electric 
current,  or  by  the  vibrations  of  a  tuning-fork,  a  pen  or  writer 


pends  on  the 
as  to  the  ac- 
tnd,  secondly, 
;ions.  Much 
Lcation  of  the 
nstrument  of 
ice  could  not ; 
B  heyond  the 
i  of  the  most 
lat  in  every 
wer  animals,, 
ly  excel  him. 
lines  of  facts 
hey  have,  as 
o  much  have 
d  heen  sharp- 

y  instruments 
iring  body  can 
idem  physiol- 
aethod,  which 
lished  French 
f  the  point  of 
ler  of  glazed 
Eiting  of  some 
,  as  shellac  in 
rittenmay  be 
ibject  is  to  get 
the  most  used 
y  be  raised  or 
f  some  sort  of 
sh  is  moved  by 
ig  complexity. 
>tild  be  of  any 
be  susceptible 
This  can  be 
ne  or  abscissa 
ecord  which  is 

first  is  easily 
a  straight  line 
[.    Time  inter- 

of  an  electric 
i  pen  or  writer 


PHYSIOLOGICAL  RESEARCH,  PHYSIOLOGICAL  REASONING.  143 

of  some  kind  being  in  each  instance  attached  to  the  apparatus 
so  as  to  record  its  movements. 

As  levers,  in  proportion  to  their  length,  exaggerate  all  the 
movements  imparted  to  them,  a  constant  process  of  correction 
must  be  carried  on  in  the  mind  in  reading  the  records  of  the 
graphic  method,  as  in  interpreting  the  field  of  view  presented 
by  the  microscope. 

The  student  is  especially  warned  to  carry  on  this  process, 
otherwise  highly  distorted  views  of  the  reality  will  become 
fixed  in  his  own  mind ;  and  certainly  a  condition  of  ignorance 
is  to  be  preferred  to  such  false  knowledge  as  this  may  become. 
But  it  is  likewise  apparent  that  movements  that  would  without 
such  mechanism  be  quite  unrecognized  may  be  rendered  visible 
and  utilized  for  inference.  There  is  another  source  of  possible 
misconception  in  the  use  of  the  graphic  method.  The  lever  is 
sometimes  used  to  record  the  movements  of  a  column  of  fluid 
(manometer.  Pig.  207),  as  water  or  mercury,  the  inertia  of  which 
is  considerable,  so  that  the  record  is  not  that  of  the  lever  as 
aflfected  by  the  physiological  (tissue)  movement,  but  that  move- 
ment conveyed  through  a  fluid  of  the  kind  indicated.  Again, 
all  points,  however  delicate,  write  with  some  friction,  and  the 
question  always  arises.  In  how  far  is  that  friction  sufficient  to 
be  a  source  of  inaccuracy  in  the  record  ?  When  organs  are  di- 
rectly connected  with  levers  or  apparatus  in  mechanical  rela- 
tion with  them,  one  must  be  sure  that  the  natural  action  of  the 
organ  under  investigation  is  in  no  way  modified  by  this  con- 
nection. 

From  these  remarks  it  will  be  obvious  that  in  the  graphic 
method  physiologists  possess  a  means  of  investigation  at  once 
valuable  and  liable  to  mislead.  Already/electricity  has  been 
extensively  used  in  the  researches  of  physiologists,  and  it  is  to 
this  and  the  employment  of  photography  that  we  look  in  the 
near  future  for  methods  that  are  less  open  to  the  objections  we 
have  noticed. 

(Jowever  important  the  methods  of  physiology,  the  results 
are  vastly  more  so.  We  next  notice,  then,  the  progress  from 
methods  and  observations  to  inferences,  which  we  shall  en- 
deavor to  make  clear  by  certain  cases  of  a  hypothetical  charac- 
ter. Proceeding  from  the  brain  and  entering  the  substance  of 
the  heart,  there  is  in  vertebrates  a  nerve  known  as  the  vagus. 
Suppose  that,  on  stii^ulating  this  nerve  by  electricity  in  a  rab- 
bit, the  heart  ceases  to  beat,  what  is  the  legitimate  inference  ? 
Apparently  that,  the  effect  has  been  due  to  the  action  of  the 


144 


ANIMAL  PHTSIOLOOT. 


nerve  on  the  heart,  an  action  excited  by  the  use  of  electricity. 
This  doefl  not,  however,  according  to  the  principles  of  a  rigid 
logic,  follow.  The  heart  may  have  ceased  beating  from  some 
cause  wholly  unconnected  with  this  experiment,  or  from  the 
electric  current  escaping  along  the  nerve  and  affecting  some 
nervous  mechanism  within  the  heart,  which  is  not  a  part  of  the 
vagus  nerve ;  or  it  may  have  been  due  to  the  action  of  the  cur- 
rent on  the  muscular  tissue  of  the  heart  directly,  or  in  some  other 
way.  But  suppose  that  invariably,  whenever  this  experiment 
is  repeated,  the  one  result  (arrest  of  the  beat)  follows,  then  it  is 
clear  that  the  vagus  nerve  is  in  some  way  a  factor  in  the  causa- 
tion. Now,  if  it  could  be  ascertained  that  certain  branches  of 
the  nerve  were  distributed  to  the  heart-muscle  directly,  and  that 
stimulation  of  these  gave  rise  to  arrest  of  the  cardiac  pulsation, 
then  would  it  be  highly  probable,  though  not  certain,  that  there 
was  in  the  first  instance  no  intermediate  mechanism;  while 
this  inference  would  become  still  more  probable  if  in  hearts 
totally  without  any  such  nervous  apparatus  whatever,  such  a 
result  followed  on  stimulation  of  the  vagus.  Suppose,  further, 
that  the  application  of  some  drug  or  poison  to  the  heart  pro- 
vided with  special  nervous  elements  besides  the  vagus  termi- 
nals prevented  the  effect  before  noticed  on  stimulating  the 
vagus,  while  a  like  result  followed  under  similar  circumstances 
in  those  forms  of  heart  unprovided  with  such  nervous  struct- 
ures, there  would  be  additional  evidence  in  favor  of  the  view 
that  the  result  we  are  considering  was  due  solely  to  some  action 
of  the  vagus  nerve ;  while,  if  arrest  of  the  heart  followed  in  the 
first  case  but  not  in  the  second,  and  this  result  were  invariable, 
there  would  be  roused  the  suspicion  that  the  action  of  the 
vagus  was  not  direct,  but  through  the  nervous  structures  with- 
in the  heart  other  than  vagus  endings.  And  if,  again,  there  were 
a  portion  of  the  rabbit's  heart  to  which  there  were  distributed 
this  intrinsic  nervous  supply,  which  on  stimulation  directly 
was  arrested  in  its  pulsation,  it  would  be  still  more  probable 
that  the  effect  in  the  first  instance  we  have  considered  was  due 
to  these  structures,  and  only  indirectly  to  the  vagus.  But  be  it 
observed,  in  all  these  cases  there  is  only  probability.  The  con- 
clusions of  physiology  never  rise  above  probability,  though  this 
may  be  so  strong  as  to  be  practically  equal  in  value  to  absolute 
certainty.  Would  it  be  correct,  from  any  or  all  the  experi- 
ments we  have  supposed  to  have  been  made,  to  assert  that  the 
vagus  was  the  arresting  (inhibitory)  nerve  of  the  heart  ?  All 
hearts  thus  far  examined  have  much  in  common  in  structure 


PHYSIOLOGICAL  RESEARCH,  PHYSIOLOGICAL  REASONING.  I45 


ctricity. 
a  rigid 
>m  some 
rom  the 
ig  some 
rt  of  the 
the  cur- 
ne  other 
leriment 
hen  it  is 
e  causa- 
aches  of 
and  that 
alsation, 
lat  there 
a;  while 
n  hearts 
r,  such  a 
,  further, 
Bart  pro- 
is  termi- 
,ting  the 
mstances 
as  struct- 
the  view 
ne  action 
^ed  in  the 
ivariable, 
tn  of  the 
ires  with- 
here  were 
stributed 
L  directly 
probable 
I  was  due 
But  be  it 
The  con- 
ough  this 
>  absolute 
le  experi- 
t  that  the 
art?    All 
structure 


and  function,  and  in  so  far  is  the  above  generalization  probable. 
Such  a  statement  would,  however,  be  far  from  that  degree  of 
probability  which  is  possible,  and  should  therefore  not  be  ac- 
cepted till  more  evidence  has  been  gathered.  The  mere  resem- 
blance in  form  and  general  function  does  not  suffice  to  meet  the 
demands  of  a  critical  logic.  Such  a  statement  as  the  above  would 
not  necessarily  apply  to  the  hearts  of  all  vertebrates  or  even  all 
rabbits,  if  the  experiments  had  been  conducted  on  one  animal 
alone,  for  the  result  might  be  owing  to  a  mere  idiosyncrasy  of 
the  rabbit  under  observation.  The  further  we  depart  from  the 
group  of  animals  to  which  the  creature  under  experiment  be- 
longs, the  less  is  the  probability  that  our  generalizations  for 
the  one  class  will  apply  to  another.  It  will,  therefore,  be  seen 
that  wide  generalizations  can  not  be  made  with  that  amount  of 
certainty  which  is  attainable  until  experiments  shall  have  be- 
come very  numerous  and  widely  extended.  A  really  broad  and 
sound  physiology  can  only  be  constructed  when  this  science 
has  become  much  more  comparative — that  is,  extended  to  many 
more  groups  and  sub-groups  of  animals  than  at  present. 

(To  attempt  to  generalize  for  the  heart,  the  kidney,  the  liver, 
etc.,  when  only  the  dog,  cat,  rabbit,  and  frog,  have  been  made 
as  a  rule  the  subjects  of  experiment,  except  for  the  groups  of 
animals  to  which  the  above  belong,  is  not  only  hazardous  but 
positively  illogical ;  while  to  denominate  conclusions  based  on 
such  experiments,  even  when  supplemented  by  the  teachings 
of  disease, "  human  physiology "  is,  in  the  writer's  opinion,  a 
wholly  unwarrantable  proceeding. 

(jt  is  this  conviction  which  has  had  much  to  do  with  this 
book  being  written;  to  the  introduction  of  the  comparative 
element ;  and  the  separation  so  frequently  in  form  as  well  as 
in  reality  of  facts  and  inferences.  A  genuine  human  physi- 
ology, with  the  exact  nature  and  value  of  the  inferences  clearly 
stated,  is  yet  to  be  written ;  and  it  seems  not  only  judicious, 
but  demanded  as  a  matter  of  candor  and  honesty,  to  state  at 
the  outset  to  the  student  what  we  feel  able  to  teach  confidently, 
and  what  must  be  presented  as  feebly  probable  or  barely  pos- 
sible. 

'  Human  physiology  proper  must  of  necessity  be  accumulated 
slowly.  Much  may  be,  indeed  must  be,  inferred  from  the  ex- 
periments disease  is  making ;  still,  certain  forms  of  accident  or 
surgical  operation  provide  the  opportunity  to  investigate  the 
human  body  in  health  or  in  a  moderately  near  approach  to  that 
condition.  Close  self-observation  under  a  variety  of  condi- 
10 


■Mmm 


■giwami— Kawniat 


1P^ 


146 


ANIMAL  PHYSIOLOGY. 


tions,  SO  precisely  defined  as  to  meet  the  demanus  ,r'  science, 
may  be  made  by  the  intelligent  student.  Much  ol  '!'.''  .ratjht 
be  verified  in  the  case  of  other  healthy  persons.  Si>riifc  of  it  is 
in  certain  respects  of  more  value  than  any  experiments  thct 
can  be  made  upon  the  lower  animals,  for  the  latter  can  not 
communicate  to  us  their  sensations;  in  their  case  all  our  in- 
formation must  be  derived  from  the  use  of  our  own  senses, 
mostly  unaided  by  any  reports  of  theirs. 

^t  is  not  possible  during  any  experiment,  especially  any  one 
in  which  vivisection  is  employed,  to  observe  the  animal  under 
conditions  that  are  strictly  normal,  for,  by  the  very  nature  of 
the  case,  we  have  rendered  it  abnormal.  We  must  in  all  such 
instances  draw  conclusions  with  corresponding  caution.  It 
will  be  understood  that  the  expression  "conclusive  experi- 
ment," as  applied  to  such  a  case,  is  only  approximately  correct. 

(At  the  present  time  it  is  very  common  to  experiment  upon 
organs  disconnected,  either  anatomically  or  physiologically 
(functionally),  from  the  rest  of  the  body  to  a  greater  or  less 
extent.  This  is  termed  the  isolated  method.  It  has  the  advan- 
tage of  being  more  simple,  and  permits  of  the  study  of  certain 
points  apart  from  others — one  factor  being  considered  inde- 
pendently of  the  rest  in  the  physiological  totaL  But,  in  draw- 
ing conclusions,  it  is  very  important  in  such  a  case  not  to  forget 
the  premises.  There  is  manifest  danger  of  making  the  gener- 
alization wider  than  the  facts  warrant.  It  is  only  when  such 
experiments  are  supplemented  by  a  great  many  others,  and 
when  judged  in  connection  with  the  action  of  the  organ  under 
consideration,  as  it  is  influenced  by  other  organs,  that  such  re- 
sults can  be  of  great  value  in  building  up  a  normal  physiology. 
To  know,  for  example,  that  the  isolated  heart  behaves  in  a  cer- 
tain manner  is  not  useless  information,  but  its  value  depends 
entirely  on  the  conclusions  drawn  from  it,  especially  as  to  what 
it  is  conceived  as  teaching  of  the  functions  of  the  heart  as  it 
beats  within  the  body  of  an  animal  while  it  walks,  or  flies,  or 
swims,  in  carrying  out  the  purpose  of  its  being. 

(We  have  incidentally  alluded  to  the  teaching  of  'disease, 
"disease  "  is  but  a  name  for  disordered  function.  One  viewing 
a  piece  of  machinery  for  the  first  time  in  improper  action  might 
draw  conclusions  with  comparative  safety,  provided  he  had  a 
knowledge  of  the  correct  action  of  aimilar  machines.  Our  ex- 
perience gives  us  a  certain  knowledge  of  the  f uncticns  of  our 
own  bodies.  By  ordinary  observation  and  by  experiisent  on 
other  animals  we  get  additional  data,  which,  taken  with  the 


THE  BLOOD. 


14T 


■  science, 
<.''  rij^'ht 
lb  of  it  is 
lents  thnl 
r  can  not 
11  our  in- 
rn  senses, 

y  any  one 
mal  under 
nature  of 
n  all  such 
ution.     It 
re  experi- 
ly  correct, 
nent  upon 
iologically 
ber  or  less 
the  advan- 
of  certain 
ered  inde- 
t,  in  draw- 
it  to  forget 
the  gener- 
when  such 
»thers,  and 
*gan  under 
it  such  re- 
)hy8iology. 
es  in  a  cer- 
ue  depends 
as  to  what 
heart  as  it 
or  flies,  or 

of  disease, 
ne  viewing 
jtion  might 
i  he  had  a 
s.  Our  ex- 
icns  of  our 
eriment  on 
n  with  the 


disordered  action  resulting  from  gross  or  molecular  injury 
(disease),  gives  a  basis  for  certain  conclusions  as  to  the  normal 
functions  of  the  human  body  or  those  of  lower  animals.  This 
information  is  especially  valuable  in  the  case  of  man,  since  he 
can  report  with  a  fair  degree  of  reliability,  in  most  diseased 
conditions,  his  own  sensations. 

It  is  hoped  that  this  brief  treatment  of  the  methods  and 
logic  of  physiology  will  suffice  for  the  present.  Throughout 
the  work  they  will  be  illustrated  in  every  chapter,  though  not 
always  with  distinct  references  to  the  nature  of  the  intellectual 
process  followed. 

Sommury.— ^There  are  two  methods  of  physiological  observa- 
tion, the  direct  and  the  indirect.  The  first  is  the  simplest,  and 
is  valuable  in  proportion  to  the  accuracy  and  delicacy  and 
range  of  the  observer ;  the  latter  implies  the  use  of  apparatus, 
and  is  more  complex,  more  extended,  more  delicate,  and  precise. 
It  is  usually  employed  with  the  graphic  method,  which  has  the 
advantage  of  recording  and  thus  preserving  movements  which 
correspond  with  more  or  less  exactness  to  the  movements  of 
tissues  or  organs.  It  is  valuable,  but  liable  to  errors  in  record- 
ing and  in  interpretation. 

(  The  logic  of  physiology  is  that  of  the  inductive  sciences.  It 
proceeds  from  the  special  to  the  general.  The  conclusions  of 
physiology  never  pass  beyond  extreme  probability,  which,  in 
some  cases,  is  practically  equal  to  certainty.  It  is  especially 
important  not  to  make  generalizations  that  are  too  wide. 


THE  BLOOD. 

It  is  a  matter  of  common  observation  that  the  loss  of  the 
whole,  or  a  very  large  part,  of  the  blood  of  the  body  entails 
death ;  while  an  abundant  hsemorrhage,  or  blood-disease  in  any 
of  its  forms,  caases  great  general  weakness. 

The  student  of  embryology  is  led  to  inquire  as  to  the  neces- 
sity for  the  very  early  appearance  and  the  rapid  development 
of  the  blood- vascular  system  so  prominent  in  all  vertebrates. 

An  examination  of  the  means  of  transit  of  the  blood,  as 
already  intimated,  reveals  a  complicated  system  of  tubes  dis- 
tributed to  every  organ  and  tissue  of  the  body.  These  facts 
would  lead  one  to  suppose  that  the  blood  must  have  a  tran- 
scendent importance  in  the  economy,  and  such,  upon  the  most 
minute  investigation,  proves  to  be  the  case.    The  blood  has 


148 


ANIMAL  PHYSIOLOGY. 


been  aptly  compared  to  an  internal  world  for  the  tissues,  an- 
swering to  the  external  world  for  the  organism  as  a  whole. 
This  fluid  is  the  great  storehouse  containing  all  that  the  most 
exacting  cell  can  demand ;  and,  further,  is  the  temporary 
receptacle  of  all  the  waste  that  the  most  busy  cell  requires  to 
discharge.  Should  such  a  life-stream  cease  to  flow,  the  whole 
vital  machinery  must  stop — death  must  ensue. 

Comparative. — It  will  prove  more  scientific  and  generally  sat- 
isfactory to  regard  the  blood  as  a  tissue  having  a  fluid  and 
flowing  matrix,  in  which  float  cellular  elements  or  corpuscles — 
a  view  of  the  subject  thvit  is  less  startling  when  it  is  remem- 
bered that  the  greater  part  of  the  protoplasm  which  makes  up 
the  other  tissues  of  the  body  is  of  a  semifluid  consistence.  In 
all  animals  possessing  blood,  the  matrix  is  a  clear,  usually  more 
or  Ippg  colored  fluid.  Among  invertebrates  the  color  may  be 
pronounced :  thus,  in  cephalopods  and  some  crustaceans  it  is 
blue,  but  in  most  groups  of  animals  and  all  vertebrates  the 
matrix  is  either  colorless  or  more  commonly  of  some  slight 
tinge  of  yellow.  Invertebrates  with  few  exceptions  possess 
only  colorless  corpuscles,  but  all  vertebrates  have  colored  cells 
which  invariably  outnumber  the  other  variety,  and  display 

forms  and  sizes  which 
are  sufiiciently  constant 
to  be  characteristic.  In 
all  groups  below  mam- 
mals the  colored  corpus- 
cles are  oval,  mostly  bi- 
convex, and  nucleated 
during  all  periods  of  the 


animal's  existence ;  in 
mammals  they  are  cir- 
cular biconcave  disks 
(except  in  the  camel 
tribe,  the  corpuscles  of 
which  are  oval),  and  in 
post-embryonic  life  with- 
out a  nucleus ;  nor  do 
they  possess  a  cell-wall 
The  red  cells  vary  in  size 
in  different  groups  and 
sub-groups  of  animals,  being  smaller  the  higher  the  place  the 
animal  occupies,  as  a  general  rule:  thus,  they  are  very  large 
iu  vertebrates  below  mammals,  in  some  cases  being  almost 


Fio.  143.— loiicocytes  of  human  blood,  showing  amoB* 
bold  movementM  (Landois).  Theae  movements  are 
not  normally  in  the  Mood-Teasels  so  marked  as  pic- 
tured here,  so  that  tbu  figure  represents  an  ex- 
treme case. 


H 


THE  BLOOD. 


149 


3  tissues,  an- 
as a  whole, 
bat  the  most 
3  temporary 
1  requires  to 
w,  the  whole 

generally  sat- 
:  a  fluid  and 
corpuscles — 
it  is  remem- 
ch  makes  up 
sistence.  In 
usually  more 
!olor  may  be 
taceans  it  is 
rtebrates  the 
some  slight 
ions  possess 
colored  cells 
and  display 
sizes  which 
tly  constant 
3teristic.  In 
below  mam- 
ored  corpus- 
1,  mostly  bi- 
d  nucleated 
Briods  of  the 
:istence  ;  in 
hey  are  cir- 
icave    disks 

the  camel 
orpuscles  of 
>yal),  and  in 
nic  life  with- 
lus ;  nor  do 
I  a  cell-wall 
}  vary  in  size 

groups  and 
the  place  the 
•e  very  large 
teing  almost 


Fio. 


-Photograph  of  colored 
frog.    1  X  370.    (After  FUut. 


luscies  of 


visible  to  the  unaided  eye,  while  in  the  whole  class  of  mam- 
mals they  are  very  minute ;  their  numbers  also  in  this  group 
are  vastly  greater  than  in 
others  lower  in  the  scale. 

The  average  size  in  man 
is  TiW  inch  ("OOT?  mm.)  and 
the  number  in  a  cubic  mil- 
limetre of  the  blood  about 
5,000,000  for  the  male  and 
500,000  less  for  the  female, 
which  would  furnish  about 
250,000,000,000  in  a  pound 
of  blood.  It  will  be  under- 
stood that  averages  only  are 
spoken  of,  as  all  kinds  of 
variations  occur,  some  of 
which  will  be  referred  to 
later,  and  their  significance 
explained. 

Under  the  microscope  the  blood  of  vertebrates  is  seen  to 
owe  its  color  to  the  cells  chiefly,  and,  so  far  as  the  red  goes, 

almost  wholly.  Corpuscles 
when  seen  singly  are  never 
of  the  deep  red,  however, 
of  the  blood  as  a  whole, 
but  rather  a  yellowish  red, 
the  tinge  varying  some- 
what with  the  class  of  ani- 
mals from  which  the  spec- 
imen has  been  taken. 

Certain  other  viorpho- 
logical  elements  found  in 
mammalian  blood  deserve 
bri%f  mention,  though  their 
significance  is  as  yet  a  mat- 
ter of  much  dispute : 

1.  The  blood  -  plates 
{plaques,  TuBviatoblasfs, 
third  element),  very  small, 
colorless,  biconcave  disks,  which  are  dejwsited  in  great  num- 
bers on  any  thread  or  similar  foreign  body  introduced  into  the 
circulation,  and  rapidly  break  np  when  blood  is  shed. 

2.  On  a  slide  of  blood  that  has  been  prepared  for  some  little 


orpuwlM  from  hum«n  mibject  (Funkey. 
A  few  coiorlew  corpuackM  are  aeen  among  the 
colored  disks,  which  are  many  of  them  arranged 
In  roul«ause. 


1 


160 


ANIMAL  PHYSIOLOGY. 


time,  aggregations  of  very  minute  granules  (elementary  gran- 
ules) may  be  seen.  These  are  supposed  to  represent  the  disin- 
tegrating protoplasm  of  the  corpuscles. 


© 


»^^ 


i) 


B 


I 


Fio.  14«.— Blood-plaques  and  their  derivatiTea  (Landoia,  after  BinoEPro  and  Laker}.  1,  red 
blood-eorpuscleB  on  the  flat ;  3,  from  the  side ;  8,  unchanged  blood-plaques ;  4,  lymph- 
corpuscle  surrounded  with  biood-plaques ;  6,  btoud-plaques  varioushr  altered ;  6,  lymph- 
corpuscle  with  two  masses  of  fiised  blood-plaques  and  threads  of  flbrin ;  7,  group  of 
blood-plaques  fused  or  run  together ;  8,  similar  small  mass  of  partially  dissolved  blood- 
plaques  with  fibrils  of  flbrin. 

The  pale  or  colorleiss  corpuscles  are  very  few  in  number  in 
mammals  compared  with  the  red,  there  being  on  the  average 
only  about  1  in  400  to  600,  though  they  become  much  more 
numerous  after  a  meal.  They  are  granular  in  appearance,  and 
possess  one  or  more  nuclei,  which  are  not,  however,  readily  seen 
in  all  cases  without  the  use  of  reagents.  They  are  character- 
ized by  greater  size,  a  globular  form,  the  lack  of  pigment,  and 
the  tendency  to  amoeboid  movements,  which  latter  may  be  ex- 
aggerated in  disordered  conditions  of  the  blood,  or  when  the 
blood  is  withdrawn  and  observed  under  artificial  conditions. 
It  will  be  understood  that  these  cells  (lenrocytes)  are  not  con- 
fined to  the  blood,  bijt  abound  in  lymph  and  other  fluids. 
They  are  the  representatives  of  the  primitive  cells  of  the  em- 
bryo, as  is  shown  by  their  tendency  (like  ova)  t«  throw  out 
processes,  develop  into  higher  forms,  etc.  In  behavior  they 
strongly  suggest  Aviaeha  and  kindred  forms. 

We  may,  then,  say  that  in  all  invertebrates  the  blow!,  when 
it  exists,  consists  of  a  plasma  {liquor  sanguinis),  in  which  float 
the  cellular  elements  which  are  colorless;  and  that  in  verte- 
brates in  addition  there  are  colored  cells  which  are  always  nu- 
cleated at  some  period  of  their  existence.    The  colorless  cells 


liary  gran- 
;  the  disin- 


THE  BLOOD. 


151 


[  L«ker).  1,  rod 
ques ;  4,  lymph- 
tered ;  6,  lymph- 
in ;  7,  group  of 
diaaolvMl  blood- 


number  in 
ihe  average 
nuch  more 
arance,  and 
•eadily  seen 
I  character- 
gment,  and 
may  be  ex- 
r  when  the 
conditions, 
re  not  con- 
ther  fluids, 
of  the  em- 
throw  out 
lavior  they 

)lood,  when 
which  float 
tt  in  verte- 
always  nu- 
lorless  cells 


are  globular  masses  of  protoplasm,  containing  one  or  more 
nuclei,  and  with  the  general  character  of  amceboid  organisms. 

The  HisTORir  of  the  Blood-Cells. 

We  have  already  seen  that  the  blood  and  the  vessels  in 
which  it  flows  have  a  common  origin  in  the  mesoblastic  cells  of 
the  embryo  chick;  the  same  applies  to  mammals  and  lower 
groups.  The  main  facts  may  be  grouped  under  two  head- 
ings: 1.  Development  of  the  blood-corpuscles  during  embry- 
onic life.  2.  Development  of  the  corpuscles  in  post-embryonic 

life.  . 

In  the  bird  and  the  mammal,  cells  of  the  mesoblast  in  the 
area  opaca  give  off  processes  which  unite ;  later  they  become 
hollowed  out  {vaciwlated)^ 
and  thus  foi.a  capillaries. 
At  the  same  time  the  nuclei 
of  these  cells  multiply  {pro- 
liferate), gather  small  por- 
tions of  the  protoplasm  of 
the  main  cells  about  them, 
become  colored,  and  thus 
form  the  nucleated  corpus- 
cles of  the  embryo.  This, 
or  a  similar  process,  is  known 
to  occur  in  some  animals 
(rat)  after  birth ;  but  in  the 
human  foetus  there  is  a  grad- 
ual decline  in  the  number  of 
nucleated  cells  found  free  in 

fVia  Klnn/l    ar\i\  ftf.  hirfli  fhftv    Flo.  147.— Surface  view  from  below  of  a  Biiuai  poT- 
tne  DlOOa,  ana  at   Oirin  tney  tlonof  posterior  end  of  pelluoW  area  of  a  cfiok 

arft  v«rv  rn.r«  which  is  nrob-         o'  thlrty-slx  hours,  1  x  100  (Foster  and  Bal- 
are  very  rare,  WUlOll  is  pi  uu  j^^^.^     g      blood-corpuBcles ;  a,  Duolel,  which 

aWv     f.Vift     PARA     with     most  subiequently  become  nuclei  of  cells  formlnK 

aoiy     me     case     witu     uiubt         waUs  of  bfood-vessels ;  p.  or.  protoplasmic 
mammals  processes,  containing  nuclei  with  large  nu- 

While  the  origin  of  the 
red  cells,  as  above  described,  may  be  regarded  as  the  earliest 
and  most  general,  it  is  not  their  exclusive  source. 

When  the  liver  has  b  sen  formed  this  organ  seems  to  carry 
on  a  development  begun  in  the  spleen,  for  the  nucleated  but  as 
yet  colorless  cells  formed  in  the  spleen  seem  to  become  pig- 
mented in  the  liver. 

There  is  also  evidence  that  colored  corpuscles  may  arise  by 
endogenous  formation  in  the  lymphatic  glands. 


152 


ANIMAL  PHYSIOLOGY. 


There  is  no  doubt  that  the  greater  number  of  the  non-nucle- 
ated corpuscles  are  derived  from  the  nucleated  forms. 

Tlie  post-embryonic  development  of  colored  corpuscles  is 
-  aturally  less  understood  from  the  greater  diflBculties  attend- 


c   # 
©   O   ig 


Fio.  148. 


D'la.  ISO. 


Fio.  149. 


Fio.  151. 


Fio.  158. 


oeU  or  free  nucleus.    (1  igs.  148- 158,  after  Osier. ) 

ing  its  investigatiin.     The  following  may  be  regarded  as  a 
summary  of  the  chiof  facts  or  rather  opinions  on  this  subject: 

1.  From  the  colorless  cells ;  though,  whether  tho  nucleus 
disappears,  or  remains  to  form  the  chief  part  of  the  cell  and 
become  pigmented,  is  undetermined. 

2.  From  peculiar  cells  of  the  rod  marrow  of  the  bones  (ha  , 
trunk,  etc.),  though  there  is  also  some  doubt  as  to  whether  the 


itt^iVmi''^\iMS£iiirAiifiiii':t^ 


THE  BLOOD. 


153 


tton-nucle- 

puscles  is 
es  attend- 


2. 

),  smaller,  more 
ly  be  even  sur- 
les  of  the  bone 

to  the  ordinary 
rellB  of  red  mar- 
>>()  red  corpuscle 
uucleuB, 
from  the  cell,  a 

jBcles.  In  4  the 
prow  cells.    6, 1, 

e ;  8,  two  micro- 
lucent,  lymphoid 


arded  as  a 
18  subject : 
ho  nucleus 
he  cell  and 

(Ones  (h  ;8  ^ 
whether  the 


nuclei  of  these  cells  remain  or  not ;  but  as  all  grades  of  transi- 
tion forms  have  been  found  in  the  bone-marrow ;  sinn o  aneemia 
occurs  in  disease  of  bones;  since  the  bone-marrow  has  been 
found  in  an  unusually  active  condition  after  hasraorrhage  and 
under  other  circumstances  demanding  a  rapid  replacement  of 
lost  cells — there  seems  to  be  little  room  for  doubt  that  in  the 
adult  the  red  marrow  of  the  bones  is  the  chief  site  of  the  devel- 
opment of  red  corpuscles.  It  is  not,  however,  the  only  one,  for 
under  peculiar  stress  of  need  even  the  lymphatic  glands  pro- 
duce red  cells,  and  the  latter  have  been  seen  to  be  budded  off 
from  the  spleen  in  a  young  animal  (kid). 

The  colorless  cells  of  the  blood  first  arise  as  migrated  undif- 
ferentiated remnants  of  the  early  embryonic  cell  colonies.  That 
they  remain  such  is  seen  by  their  physiological  behavior,  to  be 
considered  a  little  later.  Afterward  they  are  chiefly  produced 
from  a  peculiar  form  of  connective  tissue  known  as  leucocy- 
tenic,  and  which  is  gathered  into  organs,  the  chief  function  of 
which  (lymphatic  glands)  is  to  produce  these  cells,  though  this 
tissue  is  rather  widely  distributed  in  the  mammalian  body  in 
other  forms  than  these. 

Summary.— i-The  student  may,  with  considerable  certainty, 
consider  the  colorless  corpuscle  of  the  blood  as  the  most  primi- 
tive ;  the  red,  derived  either  from  the  white  or  some  form  of 
more  specialized  cell ;  the  nucleated,  as  the  earlier  and  more 
youthful  form  of  the  colored  corpuscle,  which  may  in  some 
groups  of  vertebrates  be  replaced  by  a  more  specialized  (or  de- 
graded ?)  non-nucleated  form  mostly  derived  directly  from  the 
former ;  that  in  the  first  instance  the  blood-vessels  and  blood 
arise  simultaneously  in  the  mesoblastic  embryonic  tissue;  that 
such  an  origin  maj'  exist  after  birth,  either  normally  in  some 
mammals  or  under  unusual  functi  )nal  need ;  that  the  red 
marrow  is  the  chi«)f  birthplace  of  colored  cells  in  adult  life ; 
that  the  spleen,  liver,  lymphatic,  glands,  and  other  tissues  of 
similar  structure  contribute  in  a  less  degi  oe  to  the  develop- 
ment (  i  ihe  rod  corpuscles;  and  thiit  tbo  last  mentioned  organs 
are  the  chief  producers  of  the  colorless  amoeboid  blood-cells. 

(^Finally,  it  is  well  to  remember  that  Nature's  resoxirces  in 
this,  as  in  many  other  cases,  are  numerous,  and  that  her  mode 
c>f  procedure  is  not  invariable ;  and  that,  if  oue  road  to  an  end  is 
blocked,  another  is  taken. 

The  Decline  and  Death  of  the  Blood-Cella.— The  bLjod-corpuscles, 
like  other  cells,  have  a  limited,  duration,  with  the  u.><ual  chapters 
in  a  biological  history  of  rise,  maturity,  and  decay.    There  is 


.tmiitrmimtm 


niutiiim 


154 


ANIMAL  PHYSIOLOGY. 


reason  to  believe  that  the  red  cells  do  not  live  longer  than  a 
few  weeks  at  most.  The  red  cells,  in  various  degrees  of  disor- 
ganization, have  been  seen  within  the  white  cells  (phagocytes), 
and  the  related  cells  of  the  spleen,  liver,  bone-marrow,  etc.  In 
fact,  these  cells,  by  virtue  of  retained  ancestral  (amcRboid)  quali- 
ties, have  devoured  the  weakened,  dying  red  cells.  It  seems  to 
be  a  case  of  survival  of  the  fittest.  It  is  further  known  that 
abundance  of  pigment  containing  iron  is  found  in  both  spleen 
and  liver ;  and  there  seems  to  be  no  good  reason  for  doubting 
that  the  various  pigments  of  the  secretions  of  the  body  {urine, 
bile,  etc.)  are  derived  from  the  universal  pigment  of  the  blood. 
Thebe  coloring  matters,  then,  are  to  be  regarded  as  the  excreta 
in  the  first  instance  of  cells  behaving  like  amoeboids,  and  later 
as  the  elaborations  of  certain  others  in  the  kidney  and  else- 
where, the  special  function  of  which  is  to  get  rid  of  waste 
products.  The  birth-rate  and  the  death-rate  of  the  blood- 
cells  must  be  in  close  relation  to  each  other  in  health;  and 
some  of  the  gravest  disturbances  arise  from  decided  changes 
in  the  normal  proportions  of  the  cell&  {ancemia,  le^cocythe- 
mia). 

Both  the  red  and  white  corpuscles  show,  like  all  other  cells 
of  the  organism,  alterations  corresponding  to  changes  in  the 
surrounding  conditions.  Tlia  blood  may  be  withdrawn  and  its 
cells  more  readily  observed  than  those  oi"  most  tissues ;  so  that 
the  study  of  the  influence  of  temperature,  feeding  of  the  leuco- 
cytes, and  the  action  of  reagents  in  both  classes  of  cells  is  both 
of  practical  importance  and  theoretic  interest,  and  will  well  re- 
pay the  student  for  the  outlay  in  time  and  labor,  if  attention  is 
directed  chiefly  to  the  results  and  the  lessons  they  convey,  and 
not,  as  too  commonly  happens,  principally  to  the  methods  of 
manipulation. 

The  Cbcmioal  Oompoiition  of  the  Blood.— Blood  has  a  decided 
but  faint  alkaline  reaction,  owing  chiefly  to  the  presence  of 
sodiuTri  biphosphate  (NajHPO*),  a  saline  taste,  and  a  faint  odor 
characteristic  of  the  animal  group  to  which  it  belongs,  owing 
probably  to  volatile  fatty  acids.  The  specific  gravity  of  blood 
Varies  between  1045  and  lu75,  with  a  mean  of  1066 ;  the  spe- 
cific gravity  of  the  corpuscles  being  about  1105  and  of  the 
plasma  1027.  Tub  d  enrence  explains  the  sinking  of  the  cor- 
puscles in  bloiKi  withdrawn  fvom  the  vessels  and  kept  quiet. 
Much  the  same  difficulties  are  ucountered  in  attempts  at  the 
exact  determination  of  the  chemical  composition  of  the  blood, 
as  in  the  case  of  other  living  tissxies.    Plasma  alters  its  phys- 


m 


^er  than  a 
i  of  disor- 
lagocytes), 
V,  etc.  In 
yid)  quali- 
t  seems  to 
lown  that 
oth  spleen 
•  doubting 
dy  {urine, 
the  blood, 
he  excreta 
,  and  later 
and  else- 
L  of  waste 
;he  blood- 
talth;  and 
d  changes 
'eticocythe- 

other  cells 
ges  in  the 
wn  and  its 
9S ;  so  that 
the  leuco- 
)lls  is  both 
ill  well  re- 
.ttention  is 
anvey,  and 
nethods  of 

3  a  decided 
►resence  of 

faint  odor 
ngs,  owing 
by  of  blood 
►;  the  spe- 
»nd  of  the 
of  the  cor- 
kept  quiet, 
apts  at  the 

the  blood, 
H  its  phys- 


THE  BLOOD.  165 

ical  and  its  chemical  composition,  to  what  extent  is  not  exactly 
known,  when  removed  from  the  body. 

Compontion  of  Semni. — The  fluid  remaining  after  coagulation 
of  the  blood  can,  of  course,  be  examined  chemically  with  con- 
siderable thoroughness  and  confidence. 

By  far  the  greater  part  of  serum  consists  of  water;  thus,  it 
has  been  estimated  that  of  100  parts  the  following  statement 
will  represent  fairly  well  the  proportional  composition : 

Water 90parts; 

Proteids 8  to  9    " 

Salines,  fats,  and  extractives  (small  in 
quantity  and   not    readily  obtained 

free) 1  to  2  parts. 

The  proteids  are  made  up  of  two  substances  which  can  be 
distinguished  by  solubility,  temperature  at  which  coagulation 
occurs,  etc.,  known  as  paraglobtdin  and  serum-albumen,  and 
which  may  exist  in  equal  amount. 

It  is  not  possible,  of  course,  to  say  whether  these  substances 
exist  as  such  in  the  living  blood-plasma  or  not. 

The  fais  are  very  variable  in  quantity  in  serum,  depend- 
ing on  a  corresponding  variability  in  the  plasma,  in  which 
they  would  be  naturally  found  in  greatest  abundance  after 
a  meal.  They  exist  as  neutral  stearin,  palmitin,  olein,  and  as 
soaps. 

The  principal  extractives  found  are  urea,  creatin,  and  allied 
bodies,  sugar,  and  lactic  acid.  Serum  in  most  animals  contains 
more  of  sodium  salts  than  the  corpuscles,  while  the  latter  in 
man  and  snv^.e  other  mammals  contain  a  preponderating  quan- 
tity of  potassium  compounds. 

The  principal  salts  of  serum  are  sodium  chloride,  sodium  bi- 
carbonate, sodium  sulphate,  and  phosphate  in  smaller  quantity, 
as  also  of  calcium  and  magnesium  phosphate,  with  rather  more 
of  potassium  chloride. 

It  is  highly  probable  that  this  proportion  also  represents 
moderately  well  the  composition  of  plasma,  which  is,  of  course, 
from  a  physiological  point  of  view,  the  important  matter. 

Tke  Oompoiition  of  tke  Gorpuaolet. — Taken  together,  the  differ- 
ent forms  of  blood-cells  make  up  fi'om  one  third  to  nearly  one 
half  the  weight  of  the  blood,  and  of  this  the  red  corpuscles  may 
be  considered  as  constituting  nearly  the  whole. 

The  colorless  cells  are  known  to  contain  fats  and  glycogen, 
which,  with  salts,  wo  may  believe  exist  in  the  living  cells,  and, 
in  addition  to  the  proteids^  mto  which  prot^^ph^m  resolves  it- 


'liiwmiiii 


156  ANIMAL  PHYSIOLOGY. 

self  upon  the  disorganization  that  constitutes  its  dying,  lecithin, 
protagon,  and  other  extractives. 

The  prominent  chemical  fact  connected  with  the  red  corpus- 
cles is  theix'  being  composed  in  great  part  of  a  peculiar  colored 
proteid  compound  containing  iron. 

This  will  be  fully  considered  later ;  but,  in  the  mean  time,  we 
may  state  that  the  heemoglobin  is  itself  infiltrated  into  the 
meshes  or  framework  (stroma)  of  the  corpuscle,  which  latter 
seems  to  be  composed  of  a  member  of  the  globulin  class,  so  well 
characterized  by  solubility  in  weak  saline  solutions. 

The  following  tabular  statement  represents  the  relative  pro- 
portions in  100  parts  of  the  dried  organic  matter  of  the  red  cor- 
puscles : 

Hsemoglobin 90'64 

Proteids 8-67 

Lecithin 0"64 

Cholesterin 0*25 


100-00 


The  quantity  of  salts  is  very  small,  less  than  one  per  cent 
{inorganic). 

(So  much  for  the  results  of  our  analyses ;  but  when  we  con- 
sider the  part  the  blood  plays  in  the  economy  of  the  body,  it 
must  appear  that,  since  the  life-work  of  every  cell  expresses  it- 
self through  this  fluid,  both  as  to  what  it  removes  and  what  it 
adds,  the  blood  can  not  for  any  two  successive  moments  be  of 
precisely  the  same  composition ;  yet  the  departures  from  a  nor- 
mal standard  must  be  kept  within  very  narrow  limits,  other- 
wise derangement  or  possibly  death  results.  (VVe  think  that, 
before  we  have  concluded  the  study  of  the  various  organs  of 
the  body,  it  will  appear  to  the  student,  as  it  does  to  the  writer, 
that  it  is  highly  probable  that  there  are  great  numbers  of  com- 
pounds in  the  blood,  either  of  a  character  unknown  as  yet  to 
our  chemistry,  or  in  such  small  quantity  that  they  elude  detec- 
tion by  our  methods;  and  we  may  add  that  we  believe  the 
same  holds  for  all  the  fluids  of  the  body.  The  complexity  of 
vital  processes  is  great  beyond  our  comprehension. 

It  must  be  especially  borne  in  mind  that  all  the  pabulum 
for  every  cell,  however  varied  its  needs,  can  be  derived  from 
the  blood  alone ;  or,  as  we  shall  show  presently,  strictly  speak- 
ing from  the  lymph,  a  sort  of  middle-man  between  the  blood 
and  the  tissues. 

The  Quantity  and  the  Diftribntion  of  the  Blood. -/Any  attempt 


f,  lecithin, 

3d  corpiis- 
ir  colored 

n  time,  we 
I  into  the 
lich  latter 
iss,  so  well 

iative  pro- 
le red  cor- 

0-64 
8-67 
0-54 
0-25 

o-oo 

e  per  cent 

m  we  con- 
le  body,  it 
presses  it- 
id  what  it 
Bnts  be  of 
rom  a  nor- 
lits,  other- 
hink  that, 
organs  of 
bhe  writer, 
»rs  of  com- 
as yet  to 
lude  detec- 
>elieve  the 
iplexity  of 

(  pabulum 

ived  from 

jtly  speak- 

the  blood 

ly  attempt 


THE  BLOOD.  157 

to  estimate  the  total  quantity  of  blood  in  the  body  of  an  animal 
by  bleeding  is  highly  fallacious  for  various  reasons.  It  is  im- 
possible to  withdraw  all  the  blood  from  the  vessels  by  merely 
opening  even  the  largest  of  them,  and,  if  it  were,  the  original 
quantity  would  be  augmented  by  fluid  absorbed  into  them  dur- 
ing the  very  act.  No  method  has  as  yet  been  devised  that  is 
free  from  objection,  hence  the  conclusions  arrived  at  as  to  the 
total  quantity  of  blood  are  not  in  accord ;  and  in  the  nature  of 
the  case  no  accurate  estimate  can  be  made,  but  about  one  thir- 
teenth to  one  fourteenth  may  be  taken  as  a  fair  average ;  so  that 
in  a  man  of  one  hundred  and  forty  pounds  weight  there  should 
be  about  ten  pounds  of  blood ;  but,  of  course,  this  will  vary 
with  every  hour  of  the  day  and  will  be  greatest  after  a  meal. 

As  an  example  of  the  methods  referred  to,  we  give  Welck- 
er*s,  which  is  briefly  as  follows :  The  animal  is  bled  to  death 
from  the  carotid;  a  sample  of  the  defibrinated  blood  (1  cc.)  is 
saturated  with  carbon  monoxide  (CO),  which  gives  a  perma- 
nent red  color;  this  diluted  with  500  cc.  of  water  furnishes  a 
standard  sample.  The  blood-vessels  of  the  animal  are  washed 
out  with  a  '6  per  cent  solution  of  common  salt,  but  the  Out- 
flowing stream  is  colorless ;  to  this  is  added  the  fluid  obtained 
by  chopping  up  the  tissues  of  the  animal,  steeping,  washing 
out,  and  pressing.  The  whole  is  diluted  to  give  the  color  of  the 
standard  solution,  from  which  the  amount  of  blood  in  this  mixt- 
ure may  be  calculated,  since  every  500  cc.  answers  to  1  cc.  of 
blood ;  the  blood  obtained  by  bleeding  can,  of  course,  be  accu- 
rately measured. 

It  would  be  slightly  more  accurate  to  make  the  diluted 
blood  of  the  animal  operated  upon  the  standard  without  treat- 
ment with  carbon  monoxide. 

Such  a  method,  though  the  best  yet  devised,  is  open  to  ob- 
jection also,  as  will  occur  to  most  readers. 

The  relative  quantities  of  blood  in  different  parts  of  the 
body  have  been  estimated  to  be  as  follows : 

Liver one  fourth. 

Skeletal  muscles ; "       " 

Heart,  lungs,  large  arteries,  and  veins.     "       " 

.     Other  structures "       " 

The  significance  of  this  distribution  will  appear  later. 

The  Coagulation  of  the  Blood. — When  blood  is  removed  from 
its  accustomed  channels,  it  undergoes  a  marked  chemical  and 
physical  change,  termed  clotting  or  coagulation.  In  the  case 
of  most  vertebrates,  almost  as  soon  as  the  blood  leaves  the  ves- 


158 


ANIMAL  PHYSIOLOGY. 


sels  it  begins  to  thicken,  and  gradually  acquires  a  consistence 
that  may  be  compareti  to  that  of  jelly,  so  that  it  can  no  longer 
be  poured  from  the  containing  vessel.  Though  some  have  rec- 
ognized different  stages  as  distinct,  and  named  them,  we  think 
that  an  unprejudiced  observer  might  fail  to  see  that  there 
were  any  well-marked  appearances  occurring  invnriably  at  the 
same  moment,  or  with  resting  stages  in  the  process,  as  with 
the  development  of  ova. 

After  coagulation  has  reduced  the  blood  to  a  condition  in 
which  it  is  no  longer  diffluent,  minute  drops  of  a  thin  fluid 
gradually  show  themselves,  exuding  from  the  main  mass, 
faintly  colored,  but  never  red,  if  the  vessel  in  which  the  clot 
has  formed  has  been  kept  quiet  so  that  the  red  corpuscles  have 
not  been  disturbed ;  and  later  it  may  be  noticed  that  the  main 
mass  is  beginning  to  sink  in  the  center  (cupping) ;  and  in  the 
blood  of  certain  animals,  as  the  horse,  which  clots  slowly,  the 
upper  part  of  the  coagulum  (crassamentum)  appears  of  a 
lighter  color,  owing,  as  microscopic  examination  shows,  to  the 
relative  fewness  of  red  corpuscles.  This  is  the  buffy-coat,  or,  as 
it  occurs  in  inflammatory  conditions  of  the  blood,  was  termed 
by  older  writers,  the  crusta  phlogistica.  It  is  to  be  distinguished 
from  the  lighter  red  of  certain  parts  of  a  clot,  often  the  result 
of  greater  exposure  to  the  air  and  more  complete  oxidation  in 
consequence.  The  white  blood-cells,  being  lighter  than  the  red,' 
are  also  more  abundant  in  the.  upper  part  of  the  clot  (buffy- 
coat).  If  the  coagulation  of  a  drop  of  blood  withdrawn  from 
one's  own  finger  be  watched  under  the  microscope,  the  red  cor- 
puscles may  be  seen  to  run  into  heaps,  like  rows  of  coins  lying 
ngainst  each  other  (rouleaux,  Fig.  145),  and  threads  of  the 
greatest  fineness  are  observed  to  radiate  throughout  the  mass, 
gradually  increasing  in  number,  and,  at  last,  including  the 
whole  in  a  mesh^York  which  slowly  contracts.  It  is  the  forma- 
tion of  this  fibrin  which  is  the  essential  factor  in  clotting ;  the 
inclusion  of  the  blood-cells  and  the  extrusion  of  the  serum 
naturally  resulting  from  its  formation  and  contraction. 

The  great  mass  of  every  clot  consists,  however,  of  corpus- 
cles ;  the  quantity  of  fibrin,  though  variable,  not  amounting  to 
more  usually  than  about  •?.  per  cent  in  mammals.  The  forma- 
tion of  the  clot  does  not  occupy  more  than  a  few  minutes  (two 
to  seven)  in  most  mammals,  including  man,  but  its  contraction 
lasts  a  very  considerable  time,  so  that  serum  may  continue  to 
exude  from  the  clot  for  hours.  It  is  thus  seen  that,  instead  of 
the  plasma  and  corpuscles  of  the  blood  as  it  exists  within  the 


•■•""^'"^^^ 


^Ijfj^jK^a^in^ 


-^*^3^^ 


insistence 
no  longer 
have  rec- 
,  we  think 
hat  there 
bly  at  the 
s,  as  with 

ndition  in 
thin  fluid 
ain  mass, 
h  the  clot 
scles  have 

the  main 
tnd  in  the 
ilowly,  the 
ears  of  a 
ws,  to  the 
coat,  or,  as 
'as  termed 
Anguished 
the  result 
idation  in 
an  the  red, 
lot  {buffy- 
•awn  from 
le  red  cor- 
oins  lying 
bds  of  the 

the  mass, 
uding  the 
the  forma- 
»tting;  the 
the  serum 
m. 

of  corpus- 
ounting  to 
rhe  forma- 
nutes  (two 
jontraction 
ontinue  to 
.  instead  of 
within  the 


THE  BLOOD. 


159 


living  body,  coagulation  has  resulted  in  the  formation  of  two 
new  products— serum  and  fibrin— differing  both  physically  and 
chemically.    These  facts  may  be  put  in  tabular  form  thus : 

Blood  as  it  flows  j  Liquor  sanguinis  (plasma), 
in  the  vessels.      (  Corpuscles. 

!„         ,        (  Fibrin. 
Coagulum  ^  corpuscles. 
Serum. 

As  fibrin  may  be  seen  to  arise  in  the  form  of  threads,  under 
the  microscope,  in  coagulating  blood,  and  since  no  trace  of  it  in 
any  form  has  been  detected  in  the  plasma,  and  the  process  can 
be  accounted  for  otherwise,  it  seems  unjustifiable  to  assume 
that  fibrin  exists  preformed  in  the  blood,  or  arises  in  any  way 
prior  to  actual  coagulation. 

Fibrin  belongs  to  the  class  of  bodies  known  as  proteids,  and 
can  be  distinguished  from  the  other  subrP'  isions  of  this  group 
of  substances  by  certain  chemical  as  v  s  physical  charac- 
teristics. It  is  insoluble  in  water  and  m  solutions  of  sodium 
chloride;  insoluble  in  hydrochloric  acid,  though  it  swells  in 
this  menstruum. 

It  maybe  whipped  out  .from  the  freshly  shed  blood  by  a 
bundle  of  twigs,  wires,  or  other  similar  arrangement  present- 
ing a  considerable  extent  of  surface;  and  when  washed  free 
■from  red  blood-cells  presents  itself  as  a  whitei,  stringy,  tough 
substance,  admirably  adapted  to  retain  anything  entangled  in 
its  meshes.  If  fibrin  does  not  exist  in  the  plasma,  or  does  not 
arise  directly  as  such  in  the  clot,  it  must  have  some  antecedents 
already  existing  as  its  immediate  factors  in  the  plasma,  either 
before  or  after  it  is  shed. 

We  shall  here  present  certain  facts,  and  examine  the  conclu- 
sions drawn  from  them  afterward : 

1.  Blood  may  be  prevented  from  coagulating  by  receiving  it 
in  a  solution  of  a  neutral  salt  (magnesium  sulphate,  etc.),  and 
upon  certain  chemical  treatment  precipitate  a  body  which  may 
be  obtained  by  additional  manipulation  as  a  white,  flaky  sub- 
stance, that  may  be  shown  not  to  be  fibrin,  but  which  will 
clot  and  so  give  rise  to  this  body.  Such  is  the  plasmine  of 
Denis. 

2.  By  treatment  of  plasma  with  solid  sodium  chloride,  two 
bodies  with  different  coagulating  points,  but  belonging  to  the 
same  jr-oup  of  proteids  {globulins,  soluble  in  saline  solutions), 
may  be  obtained,  denominated  paraglobulin  and  fibrinogen  re- 
spectively. 


160 


ANIMAL  PHYSIOLOGY. 


3.  Paraglobulin  may  be  obtained  from  serum  also,  and  fibrin- 
ogen from  certain  fluids  occurring  normally  {pericardial,  pleu- 
ral, etc.)  or  abnormally  (hydrocele  fluid). 

4.  Serum  added  to  these  fluids  sometimes  induces  coagula- 
tion. 

5.  Coagulation  may  occur  spontaneously  in  the  above-men- 
tioned fluids  when  removed  from  the  natural  seat  of  their  for- 
mation. 

6.  A  preparation,  made  by  extracting  serum  or  the  whipped 
(defibrinated)  blood  added  to  specimen^  of  certain  fluids  when 
they  do  not  coagulate  spontaneously,  as  hydrocele  fluid,  often 
induces  speedy  clotting. 

7.  This  extract  (fibrin-ferment)  loses  its  properties  on  boil- 
ing, and  a  very  small  quantity  suffices  in  most  cases  to  induce 
the  result.  For  these  and  other  reasons  this  agent  has  been 
classed  among  bodies  known  as  unorganized  fermenta,  which 
are  distinguished  by  the  following  properties : 

They  exert  their  influence  only  under  well-defined  circum- 
stances, among  which  is  a  certain  narrow  range  of  tempera- 
ture, about  blood-heat,  being  most  faA'orable  for  their  action. 
They  do  not  seem  to  enter  themselves  into  the  resulting  prod- 
uct, but  act  from  without  as  it  were  (catalytic  action),  hence  a 
very  small  quantity  suffices  to  effect  the  result.  In  all  cases 
they  are  destroyed  by  boiling,  though  they  bear  exposure  for* 
a  limited  prriod  to  n,  ireezhig  temperature. 

The  conclusioi^t  ■]  awT  ^"  )m  the  above  statements  are  these: 
1.  Coagulation  res  i  .  frciu  the  action  of  a  fibrin-ferment  on 
fibrinogen  and  r-;-  ■..-globulin.  2.  Coagulation  results  from  the 
action  of  a  fibri  .  i\  ^i'ment  on  fibrinogen  alone.  3.  Denis  plasmine 
is  made  up  of  fibrinogen  and  paraglobulin. 

From  observations,  microscopic  and  other,  it  has  been  con- 
cluded that  the  corpuscles  play  an  important  part  in  coagula- 
tion by  furnishing  the  fibrin-ferment ;  but  the  greatest  diver- 
sity of  opinion  prevails  as  to  which  one  of  the  morphological 
elements  of  the  blood  furnishes  the  ferment,  for  each  one  of 
them  has  been  advocated  as  the  exclusive  source  of  this  fer- 
ment by  different  observers. 

The  above  conclusions  do  not  seem  to  us  to  follow  neces- 
sarily from  the  premises.  It  might  be  true  that  a  solution  of 
fibrinogen,  on  having  fibrin-ferment  added  to  it,  would  clot,  and 
yet  it  would  not  follow  that  such  was  the  process  of  coagula- 
tion in  the  blood  itself.  All  specimens  of  hydrocele  fluid,  and 
similar  ones  not  spontaneously  coagulable,  do  not  clot  when 


,  and  fibrin- 
rdial,  pleu- 

es  coagula- 

ftbove-men- 
f  their  for- 


he  whipped 
fluids  when 
fluid,  often 

ies  on  boil- 
58  to  induce 
it  has  been 
enia,  which 

led  circum- 
)f  tempera- 
heir  action, 
ilting  prod- 
on),  hence  a 
In  all  cases 
xposure  fof 

bs  are  these : 
•ferment  on 
ts  from  the 
ais  plasmine 


IS  been  con- 
in  coagula- 
jatest  diver- 
arphological 
each  one  of 
of  this  fer- 


ollow  neces- 
Sk  solution  of 
uld  clot,  and 
of  coagula- 
)le  fluid,  and 
(t  clot  when 


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THE  BLOOD, 


161 


i 


fibrin-ferment  is  added.  Moreover,  fibrin-ferment  has  not  been 
isolated  as  an  absolutely  distinct  chemical  individual,  free  from 
all  impurities. 

OBecause  fibrinogen  and  paraglobulin  give  rise,  under  certain 
circumstances  (it  is  asserted),  to  fibrin,  and  since  plasmine  acts 
likewise,  it  does  not  follow  that  plasmine  contains  these  bodies. 
Further,  it  is  stated  that  in  the  blood. of  crustaceans  the  clot 
arises  from  the  corpuscles  chiefly,  which  run  together  and 
blend  into  a  homogeneous  mass.  The  fibrin  so  called  in  such 
a  case  differs  not  a  little  chemically,  it  could  probably  be  shown, 
if  our  tests  were  delicate  enough  to  discover  it,  from  that  which 
is  denominated  fibrin  in  other  cases.  "  Fibrin-ferment "  seems 
to  have  been  used  to  cover  much  ignorance  and  unnecessary 
invention,  as  we  shall  endeavor  to  show  later  on;  and  we  can 
not  but  regard  the  reasoning  in  regard  to  the  coagulation  of 
the  blood  as  evidence  of  an  erroneous  interpretation  of  certain 
facts  on  the  one  hand,  and  a  large  oversight  of  additional  facts 
on  the  other  hand. 

(Jn  the  mean  time  we  turn  to  certain  well-known  phenomena 
which  bear  a  clear  interpretation :  1.  The  blood  remains  fluid 
in  the  vessels  for  some  time  after  the  death  of  an  animal ;  clots 
first  in  the  larger  vessels,  and  keeps  fluid  longest  in  the  smaller 
veins.  2.  The  blood  in  the  heart  of  a  cold-blooded  animal,  as 
that  of  the  frog  or  turtle,  which  will  beat  for  days  after  the 
animal  itself  is  dead,  maintains  its  fluidity,  but  clots  at  once  on 
removal.  3.  The  blood  inclosed  in  a  large  vein  removed  be- 
tween ligatures  does  not  coagulate  for  many  hours  (twenty- 
four  to  forty-eight). 

(J'here  are  also  facts  of  an  opposite  nature,  thus :  1.  When 
blood  passes  from  a  blood-vessel  into  one  of  the  cavities  of  the 
body,  it  clots  as  if  shed  externally.  2.  If  a  ligature  be  passed 
tightly  around  an  artery  so  as  to  rupture  the  elastic  coat,  co- 
agulation ensues  at  the  site  of  the  ligature.  3.  A  similar 
clotting  results  when  the  inner  coat  of  a  blood-vessel  is  dis- 
eased, as  in  the  case  of  roughening  of  the  valves  of  the  heart 
from  inflammation,  or  the  changes  that  give  rise  to  aneurism 
of  an  artery.  4.  A  wire,  thread,  or  other  like  foreign  bodyi 
intpsduced  into  a  vein,  is  speedily  covered  with  fibrin. 

^These  facts,  and  others  of  like  character,  have  been  inter- 
preted as  indicating  that  the  living  tissues  of  the  blood-vessel  or 
heart  in  some  way  prevent  coagulation,  but  as  to  details  there 
is  difference  of  opinion.  Some  believe  that  the  fibrin-ferment 
(essential  to  coagulation,  according  to  their  view)  is  formed  by 
11 


i 


les 


ANIMAL  PHYSIOLOGY. 


K 


the  corpuscles  constantly,  but  in  the  above  cases  and  during  life 
is  not  effective  because  at  once  removed  by  the  vessel  walls ; 
while  others  are  of  opinion  that  the  living  cells  comjiosing  these 
walls  prevent  the  formation  of  the  ferment. 

Even  when  injected  into  the  blood-vessels,  fibrin-ferment 
does  not  induce  coagulation,  nor  does  the  constant  death  of  the 
blood-cells,  supposed  thus  to  give  rise  to  this  substance,  cause 
clotting. 

But  the  truth  is,  there  is  no  necessity  for  all  these  somewhat 
artificial  views,  which  seem  to  us  to  smack  more  of  the  labora- 
tory than  of  nature. 

:  We  would  explain  the  whole  matter  somewhat  thus :  "What 
the  blood  is  in  chemical  composition  and  other  properties  from 
moment  to  moment  is  the  result  of  the  complicated  interaction 
of  all  the  various  cells  and  tissues  of  the  body.  Any  one  of 
these,  departing  from  its  normal  behavior,  at  once  affects  the 
blood ;  but  health  implies  a  constant  effort  toward  a  certain 
equilibrium,  never  actually  reached  but  always  being  striven 
after  by  the  whole  organism.  The  blood  can  no  more  maintain 
its  vital  equilibrium,  or  exist  as  a  living  tissue  out  of  its  usual 
environment,  than  any  other  tissue.  But  the  exact  circum- 
stances under  which  it  may  become  disorganized,  or  die,  are 
legion ;  hence,  it  is  not  likely  that  the  blood  always  clots  in 
the  same  way  in  all  groups  of  animals,  or  even  in  the  same 
group.  The  normal  disorganization  or  death  of  the  tissue  re- 
sults in  clotting ;  but  there  may  be  death  without  clotting,  as 
when  the  blood  is  frozen,  in  various  diseases,  etc. 

To  say  that  fibrin  is  formed  during  coagulation  expresses  in 
a  crude  way  a  certain  fact,  or  rather  the  resultant  of  many 
facts.  To  explain:  When  gunpowder  and  certain  other  ex- 
plosives are  decomposed,  the  result  is  the  production  of  cer- 
tain gases.  If  we  knew  these  gases  and  their  mode  of  com- 
position but  in  the  vaguest  way,  we  should  be  in  much  the 
same  position  as  we  are  in  regard  to  the  coagulation  of  the 
blood. 

^here  is  no  difficulty  in  understanding  why  the  blood  does 
not  clot  in  the  vessels  after  death  so  long  as  they  live,  nor  why 
it  does  coagulate  upon  foreign  bodies  introduced  into  the  blood- 
stream. So  long  as  it  exists  under  the  very  conditions  under 
which  it  began  its  being,  there  is  no  reason  why  the  blood 
should  become  disorganized  (clot).  It  would  be  marvelous  if 
it  did  clot,  for  then  we  could  not  understand  how  it  could  ever 
have  been  developed  as  a  tissue  at  all.    It  is  just  as  reasonable 


d  during  life 
vessel  walls ; 
iposing  these 

)rin-ferment 

death  of  the 

stance,  cause 

)ae  somewhat 
>f  the  labora- 

;  thus :  What 
operties  from 
)d  interaction 
Any  one  of 
ae  affects  the 
3.rd  a  certain 
being  striven 
lore  maintain 
it  of  its  usual 
jxact  circum- 
d,  or  die,  are 
(vays  clots  in 
L  in  the  same 
the  tissue  re- 
nt clotting,  as 

n  expresses  in 
tant  of  many 
ain  other  ex- 
iiction  of  cer- 
node  of  com- 
in  much  the 
ilation  of  the 

he  blood  does 
live,  nor  why 
nto  the  blood- 
ditions  under 
hy  the  blood 
I  marvelous  if 
it  could  ever 
as  reasonable 


THE  BLOOD. 


168 


to  ask  why  does  not  a  muscle-cell  become  rigid  (clot)  in  the 
body  during  life. 

(Probably  in  no  field  in  physiology  has  so  much  work  been 
done  with  so  little  profit  as  in  the  one  we  are  now  discussing; 
and,  as  we  venture  to  think,  owing  to  a  misconception  of  the  real 
nature  of  the  problem.  We  can  understand  the  practical  im- 
portance of  determining  what  circumstances  favor  coagulation 
or  retard  it,  both  within  the  vessels  and  without  them ;  but 
from  a  theoretical  point  of  view  the  subject  has  been  exalted  out 
of  all  proportion  to  its  importance;  and  we  should  not  have 
dwelt  so  long  upon  it,  or  burdened  the  student  with  some  of 
the  theories  we  have  stated,  except .  in  deference  to  the  views 
held  by  so  many  physiologists. 

(It  is  not  surprising  that,  looking  at  the  subject  with  a  dis- 
torted mental  perspective,  one  theory  should  have  replaced  an- 
other with  such  rapidity.  It  is,  however,  of  practical  impor- 
tance to  the  medical  student  to  remember  some  of  the  factors 
that  hasten  or  retard,  as  the  case  may  be,  the  coagulation  of  the 
blood.  Coagulation  is  favored  by  gentle  movement,  contact 
with  foreign  bodies,  a  temperature  of  about  38°  to  40°  C,  addi- 
tion of  a  small  quantity-  of  water,  free  access  of  oxygen,  etc. 
The  process  is  retarded  by  a  low  temperature,  addition  of 
abundance  of  neutral  salts,  extract  of  the  mouth  of  the  leech, 
peptone,  much  water,  alkalies,  and  many  other  substances. 
The  excess  of  carbonic  anhydride  and  diminution  of  oxygen, 
seem  to  be  the  cause  of  the  slower  coagulation  of  venous  blood, 
hence  the  blood  long  remains  fluid  in  animals  asphyxiated.  A 
little  reflection  suffices  to  explain  the  action  of  most  of  the  fac- 
tors enumerated.  Any  cause  which  hastens  the  disintegration 
of  the  blood-cells  must  accelerate  coagulation ;  chemical  changes 
underlie  the  changes  in  this  as  in  all  other  cases  of  vital  action. 
Slowing  of  the  blood-stream  to  any  appreciable  extent  likewise 
favors  clotting,  hence  the  explanation  of  the  success  of  the 
treatment  of  aneurisms  by  pressure.  It  is  plain  that  in  all 
such  cases  the  normal  relations  between  the  blood  and  the  tis- 
sues are  disturbed,  and,  when  this  reaches  a  certain  point,  death 
(coagulation)  ensues,  as  with  any  other  tissue. 

OUiiioal  tnd  PatholiviML— The  changes  in  the  blood  that 
characterize  certain  abnormal  states  are  highly  instructive.  If 
blood  from  an  animal  be  injected  into  the  veins  of  one  of  an- 
other species,  the  death  of  the  latter  often  results,  owing  to  non- 
adaptation  to  the  blood  already  in  the  vessels,  and  to  the  tissues 
of  the  creature  generally.   The  corpuscles  break  up — the  change 


MMill^ 


164 


ANIMAL  PHYSIOLOGY. 


of  conditions  has  been  too  great.  Deficiency  in  the  quantity  of 
the  blood  as  a  whole  {oUgcemia)  causes  serious  change  in  the 
functions  of  the  body ;  but  that  a  hsemorrhage  of  considerable 
extent  can  be  so  quickly  recovered  from  by  many  persons, 
speaks  much  for  the  recuperative  power  of  the  blood-forming 
tissues.  Various  kinds  of  disturbances  in  these  blood-forming 
organs  result  in  either  deficiency  or  excess  of  the  blood-cells, 
and  in  some  cases  the  appearance  of  unusual  forms  of  corpuscles. 
(Anamia  may  arise  from  a  deficiency  either  in  the  numbers 
or  the  quality  of  the  red  cells ;  they  may  be  too  few,  deficient 


®»**° 


SS)    ^ 


Via.  IM. 


Fio.  153. 


Fio.  167. 

Fio.  168.— OutUnea  of  red  corpuwles  in  •  OMe  of  profound  Anaamla.  1, 1,  normal  corpuacles ; 
S,  Uu^  red  oorpuaole-meRiOooTte ;  S,  S,  Terr  irregular  f orma-voilUlooTtea ;  4,  very 
■mall,  deep-red  oorpuaoles— mlcroQjiiea.  . ..  ^ j.  ...        „    ^ 

Fio.  164.— Origin  of  micro(7tea  from  red  corpoaelesbjrpraatMi  of  budding  aodflaiion.  Speci- 
men from  red  marrow.  ....  ..    ^      . 

Fio.  166.— Nucleated  red  blood-corpuscle*  from  blood  in  cane  of  leukamta. 

Fio.  ise.— Oorpuaele^  containing  red  blood-corpuaole*.  1,  from  blood  of  child  at  term ;  8,  from 
blood  of  a  leuktfmio  patient.  .   .  ... 

Fio.  167.— o,  1, 8, 8;apleen-cella  containing  red  blood-corpuaclee.  b,  from  marrow ;  1,  cell  con- 
taining nine  rednorpuacle* ;  S,  cell  irtth  rrddish  granular  pigment ;  8,  fuaiform  cell  con- 
taining a  lingie  red  corpuscle.  «,  oonnectiTe-tisnie  corpuHole  from  subcutaneous  tissue  of 
young  rat,  Mowing  the  inthujelliilar  deretopment  of  red  blood-oorpuscles.  (Figs.  IS>-16i , 
after  Osier.) 

in  size,  or  lacking  in  the  normal  quantity  of  heemoglobin.  In 
one  form  {pemidoua  otuemta),  which  often  proves  fatal,  a 
variety  of  forms  of  the  red  blood-cells  may  appear  in  the  blood- 
stream ;  some  may  be  very  small,  some  larger  than  usual,  others 


le  quantity  of 
hange  in  the 

considerable 
lany  persons, 
lood-forming 
lood-forming 
e  blood-cells, 
of  corpuscles. 

the  numbers 
few,  deficient 


)     ^ 


,  nomuU  oorpuicles ; 
lioUillooTtea ;  4,  very 

iKkodflMioii.  Sped- 


faUd  at  term ;  9,  from 

marrow ;  1,  cell  con- 
8,  fiMlform  cell  con- 
iboutaneoiu  tiMue  of 
■oka.    (Flga.  1SS-1S7, 


moglobin.  In 
roves  fatal,  a 
\,T  in  the  blood- 
n  usual,  others 


THE  BLOOD. 


166 


nucleated,  etc.  Again,  the  white  cells  may  be  so  multiplied  that 
the  blood  may  bear  in  extreme  cases  a  resemblance  to  milk. 

In  these  cases  there  has  been  found  associated  an  unusual 
condition  of  the  bon,e-marrow,  the  lymphatic  glands,  the  spleen, 
and,  some  have  thought,  of  other  parts. 

The  excessive  action  of  these  organs  results  in  the  production 
and  discharge  into  the  blood-current  of  cells  that  are  immature 
and  embryonic  in  character.  This  seems  to  us  an  example  of 
a  rever.iion  to  an  earlier  condition.  It  is  instructive  also  in  that 
the  facts  point  to  a  possible  seat  of  origin  of  the  cells  in  the 
adult,  and,  taken  in  connection  with  other  facts,  we  may  say,  to 
their  normal  source.  These  blood-producing  organs,  having 
too  much  to  do  in  disease,  do  their  work  badly — ^it  is  incom- 
plete. 

Although  the  evidence,  from  experiment,  to  show  that  the 
nervous  system  in  mammals,  and  especially  in  man,  has  an  in- 
fluence over  the  formation  and  fate  of  the  blood  generally,  is 
scanty,  there  can  be  little  doubt  that  such  is  the  case,  when  we 
take  into  account  instances  that  frequently  fall  under  the  notice 
of  physicians.  Certain  forms  of  aneemia  have  followed  so  di^ 
rectly  upon  emotional  shocks,  excessive  mental  work  and  worry ,\ 
as  to  leave  no  uncertainty  of  a  connection  between  these  and  thei 
changes  in  the  blood ;  and  the  former  must,  of  course,  have  acted) 
chiefly  if  not  solely  through  the  nervous  system. 

It  will  thus  be  apparent  that  the  facts  of  disease  are  in  har- 
mony with  the  views  we  have  been  enforcing  in  regard  to  the 
blood,  which  we  may  now  briefly  recapitulate. 

Suniiuury.^^Blood  may  be  regarded  as  a  tissue,  with  a  fluid 
matrix,  in  which  float  cell-contents.  Like  other  tissues,  it  has 
its  phases  of  development,  including  origin,  maturity,  and 
death.  The  colorless  cells  of  the  blood  may  be  considered  as 
original  undifferentiated  embryo  cells,  which  retain  their  primi- 
tive character ;  the  non-nucleated  red  cells  of  the  adult  are  the 
mature  form  of  nucleated  cells  that  in  the  first  instance  are 
colorless,  and  arise  from  a  variety  of  tissues,  and  which  in 
certain  diseases  do  not  mature,  but  remain,  as  they  originally 
were  at  first,  nucleated.  When  the  red  cells  are  no  longer 
fitted  to  discharge  their  functions,  they  are  in  some  instances 
taken  up  by  amoeboid  organisms  (cells)  of  the  spleen,  liver, 
etc. 

rfhe  chief  function  of  the  red  corpuscles  is  to  convey  oxy- 
gen ;  of  the  white,  to  develop  as  required  into  some  more  differ- 
entiated form  of  tissue,  act  as  porters  of  food-material,  and 


'^W 


ammtm 


166 


ANIMAL  PHYSIOLOGY. 


probably  to  take  up  the  work  of  many  other  kinds  of  cells 
when  the  needs  of  the  economy  demand  it.  The  fluid  matrix 
or  plasma  furnishes  the  lymph  by  which  the  tissues  are  direct- 
ly nourished,  and  serves  as  a  means  of  transport  for  the  cells 
of  the  blood. 

The  chemical  composition  of  the  blood  is  highly  complex,  in 
accordance  with  the  function  it  discharges  as  the  reservoir 
whence  the  varied  needs  of  the  tissues  are  supplied ;  and  the 
immediate  receptacle  (together  with  the  lymph)  of  the  entire 
waste  of  the  body ;  but  the  greater  number  of  substances  exist 
in  very  minute  quantities.  The  blood  must  be  maintained  of 
a  certain  composition,  varying  only  within  narrow  limits,  in 
order  that  neither  the  other  tissues  nor  itself  may  suffer. 

The  normal  disorganization  of  the  blood  results  in  coagula- 
tion, by  which  a  substance,  proteid  in  nature,  known  as  fibrin, 
is  formed,  the  antecedents  of  which  are  probably  very  variable 
throughout  the  animal  kingdom,  and  are  likely  so  even  in  the 
same  group  of  animals,  under  different  circumstances ;  and  a 
substance  abounding  in  proteids  (as  does  also  plasma),  known 
as  serum,  squeezed  from  the  clot  by  the  contracting  fibrin.  It 
represents  the  altered  plasma. 

Certain  well-known  inorganic  salts  enter  into  the  composi- 
tion of  the  blood — ^both  plasma  and  corpuscles — ^but  the  princi- 
pal constituent  of  the  red  corpuscles  is  a  pigmented,  ferrugi- 
nous proteid  capable  of  crystallization,  termed  heemoglobin.  It 
is  respiratory  in  function. 


w. 


\ 


THE  CONTRACTILE  TISSUES^^^ 

That  contractility,  which  is  a  fundamental  property  in  some 
degree  of  all  protoplasm,  becoming  pronounced  and  definite, 
giving  rise  to  movements  the  character  of  which  can  be  pre- 
dicted with  certainty  once  the  foi-m  of  the  tissue  is  known,  finds 
its  highest  manifestation  in  muscular  tissue. 

Very  briefly,  this  tissue  is  made  up  of  cells  which  may  be 
either  elongated,  fusiform,  nucleated,  fnely  striated  lengthwise, 
but  non-striped  transversely,  united  by  a  homogeneous  cement 
substance,  the  whole  constituting  non-striped  or  involuntary 
muscle ;  or,  long  nucleated  fibers  transversely  striped,  covered 
with  an  elastic  sheath  of  extreme  thinness,  bound  together 
into  small  bundles  by  a  delicate  connective  tissue,  these  again 
into  larger  ones,  till  what  is  commonly  known  as  a  "muscle" 


L. 


THE  CONTRACTILE  TISSUES. 


167 


inds  of  cells 

fluid  matrix 

les  are  direct- 

for  the  cells 

y  complex,  in 

the  reservoir 

ied;  and  the 

of  the  entire 

bstances  exist 

maintained  of 

row  limits,  in 

r  suffer. 

ts  in  coagula- 

lown  as  fibrin, 

very  variable 

BO  even  in  the 

tances;  and  a 

asma),  known 

ing  fibrin.    It 

the  composi- 
)ut  the  princi- 
ented,  ferrugi- 
emoglobin.   It 


aperty  in  some 
I  and  definite, 
3h  can  be  pre- 
Is  known,  finds 

which  may  be 
ed  lengthwise, 
eneous  cement 
»r  involuntary 
iriped,  covered 
3und  together 
le,  these  again 
is  a  "muscle" 


is  formed.  This,  in  the  higher  vertebrates,  ends  in  tdugh, 
inelastic  extremities  suitable  for  attachment  to  the  levers  it 
may  be  required  to  move  {bones). 


Vm,  1G& 


Fio.  180. 


(8«ppey.) 
i  libers 


Fio.  188.— HuMmlar  flbera  from  the  urinary  bladder  of  the  hnman  wiUect.  1  k  800. 

1, 1, 1,  nuclei ;  H,  S,  S,  borders  of  some  of  the  fibers ;  S,  8,  iHolated  fibers ;  4, 4,  two  1 

Joined  together  at  S. 
Fio.  lW.-Huscular  fibers  from  tiie  aorta  of  the  calf.    1  x  800.    (Sappey.)    1, 1,  fibers  Joined 

with  each  other ;  S,  8, 8,  isolated  fibers. 


OompaTatiTe. — The  lowest  animal  forms  possess  the  power  of 
movement,  which,  as  we  have  seen  in  Amoeba,  is  a  result  rather 
of  a  groping  after  food ;  and  takes  place  in  a  direction  it  is  im- 
possible to  predict,  though  no  doubt  regulated  by  laws  definite 
enough,nf]  our  knowledge  were  equal  to  the  task  of  defining 
them.    ^^ 

Those  ciliary  movements  among  the  infusorians,  connected 
with  locomotion  and  the  capture  of  food,  are  examples  of  a  pro- 
toplasmic rhythm  of  wonderful 
beauty  and  simplicity. 

Muscular  tissue  proper  fire 
appears  in  the  Ccelenterata,  bui> 
not  as  a  wholly  independent 
tissue  in  all  cases.  In  many 
coelenterates  cells  exist,  the  low- 
er part  of  which  alone  forms  a 
delicate   muscular    fiber,  while 

the  superficial  portion  {myoblast),  composing  the  body  of  the 
cell,  may  be  ciliated  and  is  not  contractile  in  any  special 


Flo.  l«).-Hyob1a8ts  of  a  Jelly-flsh,  the  Me- 
d%ua  Aurtlia  (Ciaua). 


iwfiitfi^ 


168 


ANIMAL  PHYSIOLOGY. 


sense.  The  non-striped  muscle-cells  are  most  abundant  among 
the  invertebrates,  though  found  in  the  viscera  and  a  few  other 
parts  of  vertebrates.  This  form  is  plainly  the  simpler  and 
more  primitive.  The  voluntary  muscles  are  of  the  striped 
variety  in  articulates  and  some  other  invertebrate  groups  and 
in  all  vertebrates ;  and  there  seems  to  be  some  relation  between 
the  size  of  the  muscle-fiber  and  the  functional  power  of  the 
tissue — the  finer  they  are  and  the  better  supplied  with  blood, 
two  constant  relations,  the  greater  the  contractility. 

Whether  a  single  smooth  muscle-cell,  a  striped  fiber  {ceU),  or 
a  collection  of  the  latter  (muscle)  be  observed,  the  invariable 
result  of  contraction  is  a  change  of  shape  which  is  perfectly 
definite,  the  long  diameter  of  the  cell  or  muscle  becoming 
shorter,  and  the  short  diameter  longer. 

Ciliury  Morenentti — This  subject  has  been  already  considered 
briefly  in  connection  with  some  of  the  lower  forms  of  life  pre- 
sented for  study. 

It  is  to  be  noted  that  there  is  a  gradual  replacement  of  this 
form  of  action  by  that  of  muscle  as  we  ascend  the  auimal 
scale ;  it  is,  however,  retained  even  in  the  highest  animals  in 
the  discharge  of  functions  analogous  to  those  it  fulfills  in  the 
invertebrates. 

Thus,  in  Vorticella,  we  saw  that  the  ciliary  movements  of 
the  peristome  caused  currents  that  carried  in  all  sorts  of  parti- 
cles, including  food.  In  a  creature  so  high  in  the  scale  as  the 
frog  we  find  the  alimentary  tract  ciliated  ;  and  in  man  himself 
a  portion  of  the  respiratory  tract  is  provided  with  ciliated  cells 
concerned  with  assisting  gaseous  interchange,  a  matter  of  the 
highest  importance  to  the  well-being  of  the  mammal.  As  be- 
fore indicated,  ciliated  ceils  are  found  in  the  female  generative 
organs,  where  they  play  a  part  already  explained. 

It  is  a  matter  of  no  little  significance  from  an  evolutionary 
point  of  view,  that  ciliated  cells  are  more  widely  distributed  in 
the  fcBtus  than  in  the  adult  human  subject. 

As  would  be  expected,  the  movements  of  cilia  are  affected 
by  a  variety  of  circumstances  and  reagents :  thus,  they  are  quick- 
ened by  bile,  acids,  alkalies,  alcohol,  elevation  of  temperature 
up  to  about  40°  C,  etc. ;  retarded  by  cold,  carbonic  anhydride, 
ether,  chloroform,  etc. 

In  some  cases  their  action  may  be  arrested  and  re-estab- 
lished by  treatment  with  reagents,  or  it  may  recommence  with- 
out such  assistance.  All  this  seems  to  point  to  ciliary  action  as 
falling  under  the  laws  governing  the  movements  of  protoplasm 


THE  CONTRACTILE  TISSUES. 


169 


indant  among 
id  a  few  other 
e  simpler  and 
>f  the  striped 
te  groups  and 
ation  between 
power  of  the 
»d  with  blood, 

ity. 

1  fiber  (cell),  or 

;he  invariable 

•h  is  perfectly 

sole  becoming 

ady  considered 
ms  of  life  pre- 

icement  of  this 
nd  the  animal 

test  animals  in 
■>  fulfills  in  the 

movements  of 
sorts  of  parti- 
be  scale  as  the 
in  man  himself 
th  ciliated  cells 
I  matter  of  the  . 
mmal.  As  be- 
aale  generative 
i. 

jx  evolutionary 
r  distributed  in 

lia  are  affected 
they  are  quick- 
>f  temperature 
•nic  anhydride, 

[  and  re-estab- 
>mmence  with- 
iliary  action  as 
i  of  protoplasm 


in  gen  al.  It  is  important  to  bear  in  mind  that  ciliary  action 
may  go  on  in  the  cells  of  a  tissue  completely  isolated  from  the 
animal  to  \7hich  it  belongs,  and  though  influenced,  as  just  ex- 
plained, by  the  surroQndings,  that  the  movement  is  essentially 
automatic,  that  is,  inu  .^pendent  of  any  special  stimulus,  in  which 
respect  it  differs  a  good  deal  from  voluntary  muscle,  which 
usually,  if  not  always,  contracts  only  when  stimulated. 

The  lines  along  which  the  evolution  of  the  contractile  tissues 
has  proceeded  from  the  indefinite  outflowings  and  withdraw- 
als of  the  substance  of  Amoeba  up  to  the  highly  specialized 
movements  of  a  striped  muscle-cell  are  not  all  clearly  marked 
out ;  but  even  the  few  facts  mentioned  above  suffice  to  show 
gradation,  intermediate  forms.  A  similar  law  is  involved  in 
the  muscular  contractility  manifested  by  cells  with  other  func- 
tions. The  automatic  (self-originated,  independent  largely  of 
a  stimtdus)  rhythm  suggestive  of  ciliary  movement,  more 
manifest  in  the  earlier  developed  smooth  muscle  than  in  the 
voluntary  striped  muscle  of  higher  vertebrates,  indicating 
further  by  the  regularity  with  which  certain  organs  act  in 
which  this  smooth  muscular  tissue  is  predominant,  a  relation- 
ship to  ciliary  movement 
something  in  common  as  to 
origin — in  a  word,  an  evo- 
lution. And  if  this  be 
borne,  in  mind,  we  believe 
many  facts  will  appear  in 
a  new  light,  and  be  invested 
,  with  a  breadth  of  meaning 
they  would  not  otherwise 
possess. 

The  IrritabiUtj  of  Kmwle 
•ad  Herve. — An  animal,  as 
a  frog,  deprived  of  its 
brain,  will  remain  motion- 
less till  its  tissues  have 
died,  unless  the  animal  be 
in  some  way  stimulated.  If 
a  muscle  be  isolated  from 
the  body  with  the  nerve  to 
which  it  belongs,  it  will 
also  remain  passive;  but, 
if  an  electric  current  be  passed  into  it,  if  it  be  pricked,  pinched, 
touched  with  a  hot  body  or  with  certain  chemical  reagents. 


Fia.  ISl.— Nodes  of  lUnvier  and  lines  of  Fronuum 
(BkiiTler).  A.  IntercoaUI  nerve  of  tbe  mouw, 
treated  with  silver  nitrate.  B.  Kerve-flber  from 
the  lotaticnerTe  of  a  full-grown  ralibit.  jl.nodp 
of  Banvler ;  M,  meduUarjr  mbstanoe  rendered 
tranana>«nt  by  the  action  of  glycerine;  CV,aziii- 
cylinoer  preeenting  the  linea  m  Fromann,  which 
are  Tery  dietinct  near  the  node.  The  lines  are 
less  marked  at  a  distance  from  the  node. 


; 


jSxSSHHiJiai 


IMMMMMii 


iMMMM 


mmsm 


?;■ 


ITO 


ANIMAL  PHYSIOLOGY. 


contraction  ensues ;  the  same  happening  if  the  nerve  be  thus 
treated  instead  of  the  muscle.  The  changes  in  the  muscle  and 
the  nerve  will  be  seen  later  to  have  much  in  common ;  the  mus- 
cle alone^  however,  con/racto,  undergoes  a  visible  change  of  form. 
Now,  the  agent  causing  this  is  a  stimvlus,  and,  as  we  have 
seen,  may  be  mechanical,  chemical,  thermal,  electrical,  or  nerv- 
ous. As  both  nerve  and 
muscle  are  capable  of 
being  functionally  af- 
fected by  a  stimulus,  < 
they  are  said  to  be  irrita- 
ble; and,  since  muscle 
does  not  contract  with- 
out a  stimulus,  it  is  said 
to  be  non-atUomatic. 

Now,  since  muscle  is 
supplied  with  nerves  as 
well-  as  blood-vessels, 
which  end  in  a  peculiar 
way  beneath  the  muscle- 
covering  {aarcolemma) 
in  the  very  substance  of 
the     protoplasm     {end- 


4—5 


Via.  162.— Mode  of  termliuUioii  of  the  motor  nenrea 
(Flint,  After  Itoa«cet).  A.  Primitiye  faacieulus  of  the 
thyro-hyoid  muacle  of  the  human  subject,  and  it* 
nerve-tube:  1, 1,  primitive  muacular  fttadcului:  )i, 
nenre-tube;  8,  medullsiy  lubstMioe  of  the  tube, 
which  issaen  extendingto  the  terminal  plate,  where 
•■     •   IbenetOhthe 


it  diwippears ;  4,  terminal  plate  situated 
aarcolemma— that  la  to  aay,  between  it  and  the  ele- 
mentary flhrilUe ;  6,  B,  aarcolemma.  B.  PrimltlTe 
faacicufua  of  the  intercoatal  moade  of  the  lisard,  in  lailaiea)  it  miffht  be  that 
which  a  nerve-tube  terminatea:  1. 1.  sheath  of  the  V**''*^)*  '•'  "mS""  "«  «-"»* 
nerve-tube;  8,  nucleua  of  the  AMth  :  8,  S,  aaroo-  when  mUScle  Seemed  to 
lemma  becoming  oontlnuoua  with  the  aheath ;  4, 


medullary  aubatance  of  the  nerve-tube,  oeadng  Ije  stimulated,  aS  above 

abruptly  at  the  aite  of  the  terminal  plate ;  6, 5,  ter^  .    ', .      ,     -■    . , 

mliuU  plate ;  «,  6,  nuclei  of  the  plate ;  7, 7,  granular  indicated,  the  reSPOUSlVe 
aubatance  which  forms  the  principal  element  of  the  ^        ,.  ^         ,, 

terminal  plate  and  which  Is  continuous  with  the  contraction    WaS    really 

axis-cylinder ;  8, 8, undulations  of  the  sarcolemma  ,         ,      ,,  .,     i 

reproducing  those  of  the  flbrillte ;  9,  B,  nuclei  of  the  due  to  the  eXClted  Uerve 

**"*"  *°"°*'  terminals ;  and  thus  has 

arisen  the  question,  Is  muscle  of  itself  really  irritable  ? 

What  has  been  said  as  to  the  origin  of  muscular  tissue 


Fio.  Its.— Intrafibrlllar  tcrminatlona  of  the  motor  nerve  in  atriated  muacle,  atained  with  gold 

chloride  (Landoia). 

points  very  strongly  to  an  affirmative  answer,  though  it  does 
not  follow  that  a  property  once  possessed  in  the  lower  forms  of 


[ 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


171 


erve  be  thus 
muscle  and 

on;  themus- 

unge  of  form. 
,  as  we  have 

ical,  or  nerv- 

)h  nerve  and 
capable  of 

stionally    af- 

a  stimulus, 
to  be  irrita- 

since  muscle 
ontract  with- 
ilus,  it  is  said 

tUomatic. 
ace  muscle  is 
ith  nerves  as 
)lood  -  vessels, 

in  a  peculiar 
;h  the  muscle- 

{sarcaiemma) 
r  substance  of 
Ulasm  {end- 
might  be  that 
icle  seemed  to 
ited,  as  above 
the  responsive 
a   was   really 

excited  nerve 

and  thus  has 
»ble? 
nscular  tissue 


:le,  lUliied  with  gold 

bough  it  does 
ower  forms  of 


a  tissue  may  not  be  lost  in  the  higher ;  hence  the  resort  to  ex- 
periments which  have  long  been  thought  to  settle  the  :natter : 

1.  The  curare  experiment  may  be  thus  performed :  Lift  up 
the  sciatic  nerve  of  a  frog,  and  ligature  the  whole  limb  (ex- 
clusive of  the  nerve)  so  that  no  blood  may  reach  the  muscles ; 
then  inject  curare,  which  paralyzes  nerves  but  not  muscles, 
into  the  general  circulation  through  the  posterior  lymph-sac. 
On  stimulating  the  sciatic  nerve  the  muscles  of  the  leg  beneath 
the  ligature  contract,  while  no  contraction  of  the  muscles  of 
the  opposite  leg  follows  from  stimulation  of  its  sciatic  nerve. 
In  the  latter  case  the  curare  has  reached  the  nerve  terminals 
through  the  blood ;  in  the  former,  these  were  left  uninfluenced 
by  the  poison.  If,  now,  the  muscle  itself  be  directly  stimulated 
in  the  latter  case,  contraction  follows,  from  which  it  is  con- 
cluded that  curare  has  dastroyed  the  functional  capacity  of  the 
nerve  {ierminals),  but  not  of  the  muscle. 

2.  Stimulation  of  those  parts  of  muscles  in  which  no  nervous 
terminations  have  been  found,  as  the  lower  part  of  the  sartorius 
muscle  in  the  frog,  is  followed  by  contraction. 

3.  Certain  substances  (as  ammonia),  when  applied  directly 
to  the  muscle,  cause  contraction,  but  are  not  capable  of  pro- 
ducing this  effect  when  applied  to  the  nerve. 

From  these  and  various  other  facts  it  may  be  concluded  that 
muscle  possesses  independent  irritability. 


APPLICATIONS  OF  THE  GRAPHIC  METHOD  TO  THE  STUDY 
OP  MUSCLE  PHYSIOLOGY. 

It  is  impossible  to  study  the  physiology  of  muscle  to  the 
best  advantage  without  the  employment  of  the  graphic  method ; 
and,  on  the  other  hand,  no  tissue  is  so  Well  adapted  for  investi- 
gation by  the  isolated  method — ^i.  e.,  apart  from  the  animal  to 
which  it  actually  belongs — as  muscle ;  hence  the  convenience  of 
introducing  at  an  early  period  our  study  of  the  physiology  of 
contractile  tissue  and  illustrations  of  the  graphic  method,  the 
general  principles  of  which  have  already  been  considered. 

The  descriptions  in  the  text  will  be  brief,  and  the  student  is 
recommended  to  examine  the  figures  and  accompanying  ex- 
planations with  some  care. 

Chronograph^  Bavolviag  Oylinden^  «te.— Fig.  164  represents  one 
of  the  earliest  forms  of  apparatus  for  the  measurement  of  brief 
intervals  of  time,  consisting  of  a  simple  mechanism  for  pro- 


SHHMMttl 


(■BftU^ 


172 


ANIMAL  PHYSIOLOGY. 


ducing  the  movement  of  a  cylinder,  which  may  be  covered  with 
smoked  paper,  or  otherwise  prepared  to  receive  impressions 

made  upon  it  by  a  point  and  capa- 
ble of  being  raised  or  lowered,  and 
its  movements  regulated.  The 
cylinder  is  ruled  vertically  into 
a  certain  number  of  spaces,  so 
that,  if  its  rate  of  revolution  is 
known  and  is  constant  (very  im- 
portant), the  length  of  time  of 
any  evfmt  recorded  on  the  sen- 
sitive surface  may  be  accurately 
known.  This  whole  apparatus 
may  be  considered  a  chrono- 
graph in  a  rough  form. 

^ut  a  tuning-fork  is  the  most 
relit; We  form  of  chronograph, 
I  a  provided  it  can  be  kept  in  con- 
stant action  so  long  as  required ; 
and  is  provided  with  a  recording 
apparatus  that  does  not  cause 
enough  friction  to  interfere  with 
its  vibrations. 

Fig.  166  illustrates  one  ar- 
rangement  that  answers  these 

b',  weiritt  acting  m  motive  power ;  c,  d,    nnnditinnR  f airl  v  well 
BmainSiata  for  regulating %e  velocity   l^^nuiuoiiH  ittiriy  weii. 

of  the  cylinder ;  e,  marker  recording  a  The  marker,  Or  chronOgraph, 

line  on  cyli  '.der,  '       _  . 

in  the  more  limited  sense,  is 
kept  in  automatic  action  by  the  fork  interrupting  the  current 
from  a  battery  at  a  certain  definite  rate  answering  to  its  own 
proper  note. 


Fio.  164.— Original  chronometer,  devlaedby 
Thomaa  Young,  for  measuring  minute 
portions  of  time  (after  MoKendrick), 
a,  cylinder  revolving  on  vertical  axis ; 


Fio.  105.— Myographic  tracing,  such  as  la  obtained  when  the  cylinder  on  which  it  is  written 
does  not  revolve  during  the  contraction  of  the  muscle  (after  McKendrick).   * 


Marey's  chronograph,  which  is  represented  at  h  above,  and 
in  more  detail  below,  in  Fig.  167,  consists  of  two  electro-magnets 
armed  with  keepers,  between  which  is  the  writer,  which  has  a 


>  covered  with 
9  impressions 
oint  and  capa- 
r  lowered,  and 
pilated.  The 
rertically  into 
of  spaces,  so 
revolution  is 
tant  (very  im- 
kh  of  time  of 
d  on  the  sen- 
be  accurately 
ole  apparatus 
ed  a  chrono- 
orm. 

>rk  is  the  most 
chronogi'aph, 
B  kept  in  con- 
g  as  required ; 
th  a  recording 
oes  not  cause 
interfere  with 

;rates  one  ar- 

9,nswers  these 

j-ell. 

'  chronograph, 

ited   sense,  is 

ig  the  current 

ing  to  its  own 


m  which  tt  is  written 
cKendricIc).   * 


t  h  above,  and 
lectro-magneta 
iT,  which  has  a 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 

little  mass  of  steel  attached  to  it,  the  whole  working  in  unison 
with  the  tuning-fork,  so  that  an  interruption  of  the  current 


0(9. 

implies  a  like  change  of  position  of  the  writing-style,  which  is 
always  kept  in  contact  with  the  recording  surface. 


to?SSoh,5K^;K  Vf&S  totSJX  tuning-fork  ;  -  to  the  battery. 

Fig.  177  shows  the  arrangements  for  recording  a  dngle 
muscle  contraction,  and  Fig.  178  the  character  of  the  tracing 

obtained.  .  ^     *  xt 

A  mutele-nerve  preparation,  which  usually  consists  of  the 
gastrocnemius  of  the  frog  with  the  sciatic  nerve  attached, 


lU 


ANIMAL  PHYSIOLOGY. 


41 


clamped  by  a  portion  of  the  femur  cut  off  with  the  muscle,  is 
made,  on  stimulation,  to  raise  a  weighted  lever  which  is  at- 
tached to  a  point  writing  on  a 
cylinder  moved  by  some  sort  of 
clock-work.  In  this  case  the 
cylinder  is  kept  stationary  dur- 
ing the  contraction  of  the  mus- 
cle; hence  the  records  appear 
as  straight  vertical  lines. 
For  recording  movements  of 
S^^"temSrt?fe^«iS»Sm^  great  rapidity,  so  that  the  in- 
C:.  Ttoe  (.««  Ro«ntha).  ^^^^^  between  them  may  be 

apparent,  such  an  apparatus  as  is  figured  below  (Pig.  169)  an- 
swers well,  the  vibrations  of  a  tuning-fork  being  written  on  a 


Fia.  IflS.— Muacte-nerve  preparatton,  ahowing 
gairtrocnemiua  muacle,  sciatic  nerve,  and 


Fw.  las.'-apriiw  mro((f»ph  of  Du  Boia-BMrmond  (after  RoaeBthaD^TTiit  amngMMnta  for 
iti^Smi^wlSM  details  an  aimilar  to  tboae  for  {wndulum  myoipraph  (Fig.  177). 

blackened  glass  plate,  shot  before  a  chronograph  by  releasing 

a  spring. 

Several  records  may  be  made  successively  by  more  compli- 
cated arrangements,  as  will  be  explained  by  another  figure 
later. 

The  Apparatus  used  for  the  Stimulation  of  Muscle. 

It  is  not  only  important  that  there  should  be  accurate  and 
delicate  methods  of  recording  muscular  contractions,  but  that 


the  muscle,  is 
which  is  at- 
,  writing  on  a 
Y  some  sort  of 
this  case  the 
kationary  dur- 
•n  of  the  miis- 
3Cords  appear 
sal  lines, 
movements  of 
)  that  the  in- 
them  may  be 
(Fig.  169)  an- 
g  written  on  a 


Im)  WTMigeineiitii  for  - 
mph  (FJg.  177). 

>h  by  releasing 

f  more  compli- 
another  figure 


X  OF  MUBCLK. 

)e  accurate  and 
itions,  but  that 


APPLICATIONS  OP  THE  GRAPHIC  METHOD.  176 

there  be  equally  exact  methods  of  applying,  regulating,  and 
measuring  the  stimulus  that  induces  the  contraction. 

Fijr  170  gives  a  representation  of  the  inductonum  of  Du 
Boi8.Reymond,  by  which  either  a  single  brief  stimulation  or  a 


from  ^'•l*«r'i*'T''^SSJ^^^^S!^V^l^e^^e^  litweeii  prtai^jr  coll  and 
coU.  thiM  indM^  ««^''i  *S»?hS^^ A lume^^DM'r  to  •ttrmotod from icrew  /, 
wires  around  Bott  Iron  of  Mfpn  .SSfSEriiSSriik  iron  ceaaes  to  be  a  magnet  necea- 
wd  current  ttaiia  brrt^ :  Vmt  when  .^  W^^JJ" '^e^Suto^eated.  Thta  may 
iwilr,  and,  hammw  i^^tai^S J?^;J^    ^ S^im»y  becSarer i?om diagram,  Fte. 

^Brisa'g'iSss£?w'.2sfssi^ 

series  of  such  repeated  with  great  regularity  and  frequency 
may  be  effected.    The  apparatus  consists  essentially  of  a  pn- 


no.  171.-Dlagi»mmaUo  repwaenUtton  of  the  working  of  Big.  170  (after  Ro«nthai> 


I 


17« 


ANIMAL  PHYSIOLOGY. 


mary  coil,  secondary  coil,  magnetic  interrupter,  and  a  scale  to 
determine  the  relative  strength  of  the  current  employed.  The 
instrument  is  put  into  action  by  one  or  more  of  the  various 
well-known  galvanic  cells,  of  which  Daniell's  are  suitable  for 
most  experiments. 


Fro.  ITS. 


^»rru»".r2SSiS?&.S^"?^.s^^ 


S'usO.   The  lever 
e  lever  writes  the 


iBhrid  taegalpotae  ^^^"WheB' 
deKi«e  of  extension  effected  (Mter 
mrSt  Du  Bois-Rermowl  (after  Bosm 


welghts'sre  ptaoedTin  scftle-panF, 
r  RoaentlMl).  ^     ^    .    .    .. 

The  access  to,  or  exclusion  of  the  current  from,  the  induc- 
torium  is  effected  by  some  of  the  forms  of  keys,  a. specimen  of 
which  is  illustrated  in  Fig.  173. 

The  moist  chamber,  or  some  other  means  of  preventmg  the 
drying  of  the  preparation,  which  would  soon  result  in  impaired 
action,  followed  by  death,  is  essential.  A  moist  chamber  con- 
sists essentially  of  an  inclosed  cavity,  in  which  is  placed  some 
wet  blotting-paper,  etc.,  and  is  usually  made  with  glass  sides. 
The  air  in  such  a  chamber  must  remain  saturated  with  mowt- 
ure. 


„ti^,wkmiivtitkL* 


APPLICATIONS  OF  THE  OBAPHIC  METHOD. 


177 


^d  a  scale  to 
iployed.  The 
the  various 
e  suitable  for 


A  good  knowledge  of  the  subject  of  electricity  is  especially 
valuable  to  the  student  of  physiology.  But  there  are  a  few  ele- 
mentary facts  it  is  absolutely  necessary  to  bear  in  mind :  1.  Au 
induced  current  exists  only  at  the  moment  of  making  or  break- 
ing a  primary  (battt^i'y)  current.  2.  At  the  moment  of  making, 
the  induced  current  is  in  the  opposite  direction  to  that  of  the 
primary  current,  and  the  reverse  at  breaking.  3.  The  strength 
of  the  induced  current  varies  with  the  strength  of  the  primary 
current.  4.  The  more  removed  the  secondary  coil  from  the 
primary  the  weaker  the  current  (induced)  becomes. 

The  clock-work  mechanism  and  its  associated  parts,  as  seen 
in  Fig.  174,  on  the  right,  is  usually  termed  a  myograph. 


».  ITS. 


in  the  moistHduunber, 
I  tlw  pUteof  smoked 
pUoedf  In  Male-pan  F, 

•  may  be  attached  at  b 
I  not  pas  throuRh  the 
t  are  of  metal,  and,  on 
gr  than  the  wtraa.  a  tt 
lebment  to  a  table,  etc 

N>m,  the  induc- 
I,  a  specimen  of 


preventing  the 
ult  in  impaired 
t  chamber  con- 
is  placed  some 
ith  glass  sides, 
tted  with  moist- 


Fio.  174.— Arrangement  ot  apparatui  for  tranamimion  of  mutcular  movement  bjr  tambour* 
(after  McKendriok).  a,  italvanic  element ;  6,  prtmanr  ooU ;  e,  aeoondaty  otdl  ot  inducto- 
rinm ;  d,  metronome  tor  interrupting  primary  draift  when  induction  ourrent  ia  eent  to 
electrode*  k ;  h,  foroep*  for  femur :  fine  muacie,  whtdi  i*  not  here  repceaeated,  1*  attached 
to  tlie  receivinir  tambour  a,  by  which  movement  ii  traamitted  to  recording  tambour  e, 
whidi  write*  on  cylinder  f. 

Instead  of  muscular  or  other  movements  being  communi- 
cated directly  to  levers,  the  contact  may  be  through  columns 


Fia.  ITS.— Tambour  ot  Marey  (after  McKendrick).  a,  metaUie  caae ;  b,  thin  Indla-nibber  i 
brane;  o,  thin  disk  of  ahiminiumMppattinglqvaril,  a  amaU  portion  of  which  ciUy  la  repre- 
■entwd ;  e,  acrew  for  plaoinii  ■uppcrt  of  lever  Terttcally  orer  e  i  /,  metalUc  tuba  oommuni- 
oatinc  with  cavity  of  utmbour  for  aWchmiit  to  an  India-nibber  tube. 

It 


I 


,■ 


178 


ANIMAL  PHTBIOLOOT. 


of  air,  which,  it  will  be  apparent,  must  be  capable  of  communi- 
cating very  slight  changes  if  the  apparatus  responds  readily  to 
the  alterations  in  volume  of  the  inclosed  air. 

Fig.  175  represents  a  Marey's  tambour,  which  consists  essen- 
tially of  a  rigid  metallic  case  provided  with  an  elastic  top,  to 
which  a  lever  is  Attached,  the  whole  being  brought  into  com- 
munication with  a  column  of  air  in  an  elastic  tube.  The  work- 
ing of  such  a  mechanism  will  be  evident  from  Figs.  174  and  176. 


Flo.  178.— TMqboun  of  Mkrejr  arfwind  (or  tnnwrnlMton  of  mormnMit  (•ftar  McKendrick). 
a,  neiMag  tambour ;  b,  ImlU-ruDber  tube ;  e.  regiitwring  tambour ;  d,  nplnl  at  wire, 
owlBg  to  elMtlcity  at  which,  when  toniion  is  removed  from  a,  the  leTer  Mcenda. 

The  greatest  danger  in  the  use  of  such  apparatus  is  not  fric- 
tion but  oscillation,  so  that  it  is  possible  that  the  original  move- 
ment may  not  be  expressed  alone  or  simply  exaggerated,  but 
also  complicated  by  additions,  for  which  the  apparatus  itself  is 
responsible. 

Apparatus  of  this  kind  is  not  usually  employed  much  for 
experiments  with  muscle;  such  an  arrangement  is,  however, 
shown  in  Fig.  174,  in  which  all  will  be  seen — ^a  metronome,  the 
pendulum  of  which,  by  dipping  into  cups  containing  mercury, 
makes  the  circuit.  Such  or  a  simple  clock  may  be  utilized  for 
indicating  the  longer  intervals  of  time,  as  seconds. 

A  Single  Simple  Muscular  Contraction. 

Xqtriamtal  Tkoto. — The  phases  in  a  single  twitch  or  muscu- 
lar contraction  may  be  studied  by  means  of  the  pendulum 


lonsists  essen- 
Blastic  top,  to 
yht  into  com- 
e.  Thework- 
B.  174  and  176. 


It  (after  McKendritA). 
or ;  d,  tpiral  o(  wire, 
rer  uoenda. 

ituB  is  not  frio> 
original  move- 
caggerated,  but 
paratus  itself  is 

oyed  much  for 
nt  is,  however, 
metronome,  the 
ining  mercury, 
be  utilized  for 
ds. 


iCTION. 

mtch  or  muscu- 
the  pendulum 


ii 


180 


ANIMAL  PHTSIOLOOY. 


the  ■craw,  d,  to  in  eieotrlooontiiiui^  with  the  wire,*,  of  the  Mine  primuT  coil.  Thesr:  'it, 
(I,  uA  the  rod.  c,  are  provided  wltnplatinum  poinu.  and  both  we  inanlMed  br  tuMtt  oi 
the  ebonite  block,  e.  The  circuit  of  the  priBUwy  oul  to  which  «  and  y  bekMV  ■  cloaed  ■• 
lonR  M  <*  and  d  are  in  contact  When  in  fta  awiiic  the  tooth,  a',  knocks  e  away  from  <f ,  the 
oircuit  to  immediately  broken,  and  a  "breakinK^'ahook  to  aent  through  the  electrodes  con- 
nected with  the  secondary  coil  of  the  machine,  and  so  throng  the  nerre.  The  lerer,  {,  the 
end  only  of  which  to  shown  in  the  figure,  to  bn>u|At  to  bear  on  the  glass  plate,  and  when  at 
rest  describes  an  aro  of  a  circle  of  large  radlua.  ilie  tuning-fork, /lends  only  seen),  serres 
to  mark  the  time  (after  Foster). 


myograph  (Fig.  177).  It  consists  of  a  heavy  pendulum,  which 
swings  from  a  position  on  the  right  to  a  corresponding  one  on 
the  left,  where  it  is  secured  by  a  catch.  During  the  swing  of 
the  pendulum,  which  carries  a  smoked  glass  plate  (by  means 
of  arrangements  more  minutely  described  below  the  figure),  a 
tuning-fork  writes  its  vibrations  on  the  plate,  on  which  is 
inscribed  the  marking  indicating  the  exact  moment  of  the 
breaking  of  an  electric  current,  which  gives  rise  to  a  muscle 
contraction  that  is  also  recorded  on  the  plate. 

The  tracing  on  analysis  presents :  1.  The  record  of  a  tuning- 
fork  making  one  hundred  and  eighty  vibrations  in  a  second. 
2.  The  parallel  marking  of  the  lever  attached  to  the  muscle 
before  it  began  to  rise.  3.  A  curve,  at  first  rising  slowly,  and 
then  rapidly  to  a  maximum.  4.  A  curve  of  descent  similar  in 
character,  but  somewhat  more  lengthened. 

We  may  interpret  this  record  somewhat  thus:  1.  A  rise  of 
the  lever  answering  to  the  shortening  of  the  muscle  to  which  it 


a  h 


¥m.  178.— Muscle-curre  obtained  by  the  pendulum  niyagraph  (niatar).    Bead  fMm  left  to 
right   The  latent  period  to  indicated  fy  the  apace  between  a  and  b,  the  length!  qf  which  to 


meaaur^d  by  the  waves  of  a  tuntn, 
in  a  second;  and  in  like  manner  I 
be  estimated. 


r  one  hundred  and  entity  double  TibraUoas 
I  the  other  iduMca  of  the  contraction  may 


is  attached  following  upon  the  momentary  induction  shock,  as 
the  entrance  of  the  current  into  the  nerve,  the  stimulation  of 
which  causes  the  contraction,  may  be  called.  3.  A  period  before 
the  contraction  begins,  which,  as  shown  by  the  time  marking, 

occupies  in  this  case  r^,  or  about  ij^  of  a  second.   In  the  tracing 

the  upward  curve  indicates  that  the  contraction  is  at  first  rela- 


rooil.  Tbemijif, 
I  br  mrmrn  ci 
llwloaKbclaMd  •• 
le  Away  from  d,  the 
I  the  electrodea  oon- 
The  lever,  (,  the 
i  pUte,  and  wh«i  at 
'  I  only  seen),  serre* 


.ulum,  which 
Inding  one  on 

the  swing  of 
,te  (by  means 
the  figure),  a 

on  which  is 
>ment  of  the 
)  to  a  muscle 

i  of  a  tuning- 
B  in  a  second. 
o  the  muscle 
ig  slowly,  and 
ant  similar  in 


1.  A  rise  of 
cle  to  which  it 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


181 


tively  slow,  then  more  rapid,  and  again  slower,  till  a  brief  sta- 
tionary period  is  reached,  when  the  muscle  gradually  but  rap- 
idly returns  to  its  previous  condition,  passing  through  the  same 
phases  as  during  contraction  proper.  In  other  words,  there  is 
a  period  of  rising  and  of  falling  energy,  or  of  contraction,  and 
relaxation.  4.  A  period  during  which  invisible  changes,  as 
will  be  explained  later,  are  going  on,  answering  to  those  in  the 
nerve  that  cause  the  molecular  commotion  in  muscle  which 
precedes  the  visible  contraction  —  the  latent  period,  or  the 
period  of  latent  stimulation. 

The  facts  may  be  briefly  stated  as  follows :  The  stimulation 
of  a  muscle  either  directly  or  through  its  nerve  causes  contrac- 
tion, followed  by  relaxation,  both  of  which  are  preceded  by  a 
latent  period,  during  which  no  visible  but  highly  important 
molecular  changes  are  taking  place.  The  whole  chain  of  ev^its 
is  of  the  briefest  duration,  and  is  termed  a  muscle  contraction. 
The  tracing  shows  that  the  latent  period  occupied  rather  more 
than  ^  second,  the  period  of  contraction  proper  about  t^, 
and  of  relaxation  ^^  second,  so  that  the  whole  is  usuitUy  begun 
and  ended  within  Vr  second;  yet,  as  will  be  learned  later, 
many  chemical  and  electrical  phenomena,  the  concomitants  of 
vital  change,  are  to  be  observed. 

In  the  case  just  considered  it  was  assumed  that  the  muscle 
was  stimulated  through  its  nerve.  Precisely  the  same  results 
would  have  followed  had  the  muscle  been  caused  to  contract 
by  the  momentary  application  of  a  chemical,  thermal,  or  me- 
chanical stimulus. 

If  the  length  of  nerve  between  the  point  of  stimulation  and 
the  muscle  was  considerable,  some  difference  would  be  observed 


.  Bead  ttom  left  to 
ttefengr^orwhiohis 
fbty  double  ilfaratiaiiB 
the  oontraotion  majr 


ction  shock,  as 
stimulation  of 
L  period  before 
time  marking. 

In  the  tracing 

is  at  first  rela- 


Fio.  ITS.— Dtagrammatio  repwcntatloa  ot  the  meawrement  of  yekwitr  of  Derroua  impulse 
(Feeler).  Tracing  taken  b/  pendulum  mjrocraph  (Fig.  177).  The  nerre  of  lame  muacle- 
nerve  preparation  iaatlmuiatad  in  one  caae  aa  nur  aa  poaiible  from  maecle,  in  the  other  aa 
neartoitaa  pomible.  Latent  period  ia  a6,  oft*,  reapective^.  Diflttenoe  between  oA  and 
oylwttMttML  of  ooorae.  Iragth  of  time  oecnpled  bgr  nervooa  impulae  in  travrilng  along 

in  the  latent  period  if  in  a  second  case  the  nerve  were  stimu- 
lated, say,  close  to  the  muscle.    This  is  repreflented  in  Fig.  179, 


tiiUISgiimmsti-- 


IT 


189 


ANIMAL  PHTSIOLOGT. 


in  which  it  is  seen  that  the  latent  period  in  the  latter  case  is 
shortened  by  the  distance  from  b'  to  b,  which  must  be  owing 
to  the  time  required  for  those  molecular  changes  which,  occur- 
ring in  a  nerve,  give  rise  to  a  contraction  in  the  muscle  to  which 
it  belongs ;  in  fact,  we  have  in  this  method  a  means  of  estimat- 
ing the  rate  at  which  these  changes  pass  along  the  nerve — ^in 
other  words,  we  have  a  means  of  measuring  the  speed  of  the 
propagation  of  a  nervous  impulse.  The  estimated  rate  is  for  the 
frog  twenty-eight  metres  per  second,  and  for  man  about  thirty- 
three  metres.  As  the  latter  has  been  estimated  for  the  nerve, 
with  its  muscle  in  position  in  the  living  body,  it  must  be  re- 
garded rather  as  a  close  approximation  than  as  exact  as  the 
other  measurements  referred  to  in  this  chapter. 

It  will  be  borne  in  mind  that  the  numbers  given  as  repre- 
senting the  relative  duration  of  the  events  vary  with  the  ani- 
mal, the  kind  of  muscle,  and  a  variety  of  conditions  affecting 
the  same  animal. 


Tetanic  Contbaction. 

It  is  well  known  that  a  weight  may  be  held  by  the  out- 
stretched arm  with  apparently  perfect  steadiness  for  a  few 
seconds,  but  that  presently  the  arm  begins  to  tremble  or  vi- 
brate, and  soon  the  weight  must  be  dropped.  The  arm  was 
maintained  in  its  position  by  the  joint  contraction  of  several 
muscles,  the  action  of  which  might  be  described  (traced)  by  a 
writer  attached  to  the  hand  and  recording  on  a  moving  sur- 
face. Such  a  record  would  indicate  roughly  what  had  hap- 
pened ;  but  the  exact  nature  of  a  muscular  contraction  in  such 
a  case  can  best  be  learned  by  laying  bare  a  single  muscle,  say 
in  the  thigh  of  a  frog,  and  arranging  the  experiment  so  that  a 
graphic  record  shall  be  made. 

Using  the  apparatus  previously  described  (Fig.  177),  a  second 
induction  shock  may  be  sent  into  the  muscle  before  the  effect 


Flo.  180.— TtMiiiK of  » double  mowoUur oontraetioii OVMtar).  Ataooiid  ioduotioa  diook WM 
■MitiiitomiiicieiriienitlMdwteroompletod  ita  oootraoUan  m  to  ImUeaited  hr  twgiiuiliiK 
of  MooDd  riM.   DoMad  line  indicstM  what  the  carra  would  have  tem  but  tor  uitoT 


>iii«iriiMi<iiiiMiii>i<iiiiiiiiiiii«<Mattii»)a»«iiiMii<fl  I 


latter  case  is 
ust  be  owing 
(irhicli,  ocour- 
iBcle  to  which 
as  of  estimat- 
the  nerve — ^in 
speed  of  the 
rate  is  for  the 
about  tbirty- 
for  the  nerve, 
t  must  be  re- 
exact  as  the 

iven  as  repre- 
with  the'ani- 
iions  affecting 


d  by  the  out- 
ess  for  a  few 
remble  or  vi- 
The  arm  was 
ion  of  several 
(traced)  by  a 
i  moving  sur- 
rhat  had  hap- 
Action  in  such 
;le  muscle,  say 
aent  so  that  a 


APPLICATIONS  OP  THB  GRAPHIC  METHOD.  188 

of  the  first  has  passed  away,  the  result  depending  on  ttie  phase 
of  the  contraction,  during  which  the  stimulus  acts  on  the  mus- 
cle Thus,  if  a  second  shock  be  applied  during  the  latent  pe- 
riod, no  visible  change  in  the  nature  of  the  muscle-curve  can  be 
seen  •  but  if  during  one  of  the  other  phases  of  contraction,  a  re- 
sult like  that  figured  below  (Fig.  180)  follows.  If  a  series  of 
such  shocks  be  sent  into  the  muscle  before  its  contraction  pe- 
riod is  over,  a  succession  of  curves  may  be  superposed  on  one 


Fib.  ML-Ourreol  HnV^ffit^**9'^,''SSS!^J£SSS'l 


„_  trwstog  toiUttrtfB  con- 
;  lower,  ttnw-maridng*  ^ 


the  ead  »  "  oontrMsUoB  NBMiiMcr. 

another,  to  the  total  height  of  which,  however,  there  is  a  limit, 
no  matter  what  the  strength  of  the  stimulus  used. 

If  the  stimuli  foUow  each  other  with  a  certain  rapidity,  such 
a  tracing  as  that  represented  in  Fig.  181  is  obtained ;  and  if  the 
rapidity  of  the  stimuhition  exceeds  a  certain  rate,  the  result  is 
that  seen  in  Fig.  182. 


f.  177),  a  second 
•fore  the  effect 


1  Induotion  dMok  m> 
ndieated  1v  bei^niiiiig 
m  but  tor  this. 


Flo.  iM.-<3iir»e  of  complete  teUuilccoiitr«jtton(Foitor). 

It  is  possible  to  see  in  these  tracings  a  genetic  relation,  the 
second  figure  being  evidently  derivable  from  the  first,  and  the 
third  from  the  second,  by  the  fusion  of  all  the  curves  into  one 

straight  line.  ,    ,   ■.  i.  v.  j  j 

If  a  muscle,  isolated  as  we  have  described,  be  ^f^hed  dur- 
ing the  period  that  it  is  writing  the  second  and  the  third 


r 


184 


ANIMAL  PHTSIOLOOT. 


tracing,  it  may  be  observed  that,  during  that  corresponding  to 
the  former,  though  it  is  shortened,  it  does  not  remain  equally  so 
throughout,  while  during  the  writing  of  the  third  tracing  there 
is  no  variation  in  its  condition  appreciable  by  the  eye.  What 
has  happened  is  this :  The  muscle  during  the  condition  figured 
in  the  second  tracing  has  periods  of  alternating  contraction  and 
partial  relaxation,  but  during  the  third  case  the  latter  phase 
has  been  apparently  omitted — the  muscle  remains  in  continuous 
contraction.  In  reality  this  is  not  the  case  unless  we  are  mis- 
taken as  to  the  meaning  of  the  muscle-sound. 

The  MwwU  Tom. — There  are  a  number  of  experimental  facts 
from  which  important  conclusions  have  been  drawn,  to  which 
attention  is  now  directed : 

1.  It  has  been  found  that  a  sound  may  be  heard  in  a  still 
room  when  one  brings  the  muscles  of  mastication  into  action 
by  biting  hard;  or  listens  over  a  contracting  bicei)s  with  a 
stethoscope,  etc. 

2.  When  the  wires  of  a  telephone  (communicator)  are  con- 
nected with  a  muscle,  a  sound  is  heard  during  the  contraction 
of  the  muscle. 

From  these  facts  it  was  concluded  that  a  muscle  when  con- 
tracting gives  rise  to  a  sound ;  that  ietanua,  as  the  form  of  con- 
traction we  are  describing  is  called,  is  essentially  vibratory  in 
character,  which  seems  to  answer  to  the  graphic  representations 
from  a  muscle  when  in  tetanic  contraction,  and  is  in  harmony 
with  the  case  to  which  we  called  attention  at  the  commence- 
ment of  this  subdivision  of  the  subject.  The  note  heard  cor- 
responded, in  the  case  of  an  isolated  muscle,  to  the  number  of 
stimulations  per  second ;  while  for  muscles  made  to  contract  by 
the  will  the  note  was  always  the  same,  answering  to  about 
forty  vibrations  per  second;  but  as  forty  stimuli  are  not  re- 
quired within  this  period  of  time  to  induce  tetanus,  it  was 
thought  that  this  note  was  probably  the  harmonic  of  a  lower 
one  answering  to  twenty  vibrations  in  a  second. 

■  It  has  been  recently  shown  that  a  very  much  smaller  num- 
ber of  vibrations  of  the  muscle  can  give  rise  to  an  audible 
soimd,  so  that  the  explanation  it  would  seem  must  now  be 
modified;  and  it  is  likely  that  some  peculiarities  of  the  ear 
itself  must  be  taken  into  the  account  in  the  explanation.  In 
making  the  observations  referred  to  above  (in  1),  the  student 
will  find  it  very  Important  to  be  on  his  guard  against  sources 
of  error,  especially  with  the  use  of  a  stethoscope. 

We  may  safely  conclude  that,  at  all  events,  most  of  the  mus- 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


185 


Bsponding  to 
tin  equally  so 
[  tracing  there 
eye.    What 
lition  figured 
^ntraction  and 
latter  phase 
n  continuous 
we  are  mis- 
mental  facts 
ivrn,  to  which 

lard  in  a  still 
>n  into  action 
biceps  with  a 

ator)  are  con- 
le  contraction 

icle  when  con- 
le  form  of  con- 
y  vibratory  in 
'epresentations 
is  in  harmony 
he  commence- 
ote  heard  cor- 
;he  number  of 
to  contract  by 
tring  to  about 
ili  are  not  re- 
etanus,  it  was 
uic  of  a  lower 

L  sinaller  num- 
to  an  audible 
must  now  be 
ies  of  the  ear 
planation.  In 
I),  the  student 
gainst  sources 


cular  contractions  occurring  within  the  living  body  are  tetanic 
— i.  e.,  the  muscle  is  in  a  condition  of  shortening,  with  only  very 
brief  -i  nd  slight  phases  of  relaxation ;  and  that  a  comparatively 
small  number  of  individual  contractions  suffice  for  tetanus 
when  caused  by  the  action  of  the  central  nervous  system; 
though,  as  proved  by  experiments  on  muscle  removed  from  the 
body,  they  may  be  enormously  increased.  While  a  few  stimu- 
latiot  s  per  second  suffice  to  cause  tetanus,  it  will  also  persist 
thougli  thousands  be  employed. 

The  Strength  of  the  Btlmiiliu.— We  have  assumed  that  in  the 
cases  of  contraction  thus  far  considered  the  stimulus  was  ade- 
quate to  produce  the  full  amount  of  contraction,  or  as  much  as 
could  be  obtained.  Such  a  contraction  and  such  a  stimulus  are 
spoken  of  as  maximal;  but  the  stimulus  might  fall  a  little 
short  of  this,  and  is  then  termed  stib-maa;imal ;  or  it  may  be  re- 
garded from  the  point  of  view  of  being  the  least  that  will  cause 
a  contraction,  and  is  then  the  minimal  stimulus. 

It  is  important  to  note  that  any  sudden  change  in  an  electric 
current  will  act  as  an  excitant  to  muscular  contraction,  but 
that  very  considerable  changes  in  the  strength  of  the  current  if 
made  gradually  do  not  roadt  on  the  muscle.  It  sometimes  hap- 
pens that  a  sudden  onward  push  of  the  secondary  coil  of  an 
induction-machine  will  produce  either  a  tetanus  (though  the 
terminal  wires  or  electrodes  were  arranged  for  a  single  induc- 
tion shock)  or  what  is  known  as  a  supermaximal  contraction — 
i.  e.,  one  in  excess  of  what  could  be  obtained  by  more  gradual 
advances,  which  have  no  effect  usually  after  a  certain  maxi- 
mum of  contraction  is  reached.  This,  we  think,  a  loatter  of 
conBiderable  practical  importance,  and  shall  refer  to  its  signifi- 
cance in  a  later  chapter. 

Since  the  opening  or  closing  of  a  key  which  makes  or  breaks 
the  current  really  implies  a  very  great  change  in  the  strength 
of  the  current  affected  suddenly — ^that  is  in  fact  from  0  to  some 
+  quantity  or  the  reverse — we  find  that  usually  the  most  marked 
contractions  occur  only  at  these  times,  and  -this  holds,  whether 
the  current  be  slowly  or  rapidly  made  and  broken  (inter- 
rupted). 

The  nerve  being  the  natural  means  of  conveying  a  stimu- 
lus, it  is  easy  to  understand  how  the  contraction  happens  to 
follow  most  perfectly  and  with  less  strength  of  stimulus  when 
this  structure  is  excited. 


A] 


>8t  of  the  mus- 


niK;^«Mli>MA<n  r-gK-lii 


L^^.  jtTT^"  "a'T'Ti^^' 


186 


ANIMAL  PHYSIOLOGY. 


The  Changes  in  a  Muscle  during  Contraction. 

Though  the  change  in  form  is  very  great  during  the  con- 
traction of  a  muscle,  the  change  in  bulk  is  almost  inappreci- 
able, amounting  to  a  diminution  of  not  more  than  about  tVvt 
of  the  volume.  In  fact,  according  to  the  latest  investigator, 
there  is  no  diminution  whatever.  A  series  of  levers  may  be 
laid  on  a  muscle  or  the  columns  of  air  in  a  series  of  Marey's 
tambours  may  be  influenced  by  the  contracting  muscle,  and 
from  some  such  apparatus  a  graphic  record  like  that  seen  in 
Fig.  183  may  be  obtained. 

It  is  to  be  observed  that  the  contraction  passes  along  the 
muscle  in  the  form  of  a  wave,  the  size  and  speed  of  which  are 


Fia.  183.-  Tradng  of  the  propagation  of  the  muncular  wave.    ObronoRraphic  tracing,  one 
hundred  Tibratknw  per  eeoond  underneath  (Many). 


susceptible  of  measurement.  For  the  frog  the  wave-length  is 
estimated  at  from  200  to  400  nun.,  and  the  velocity  at  about  3 
to  4  metres  per  second. 

It  is  probably  rather  greater  in  the  muscles  of  mammals 
and  greater  under  the  more  natural  conditions  of  the  muscle  in 
the  intact  living  body. 

But  since  the  fibers  of  striped  muscle  are  of  very  limited 
length  (30  to  40  mm.),  it  would  seem  that  a  contraction  origi- 
nating in  one  fiber  must  be  capable  of  initiating  a  similar 
action  in  its  neighbor ;  and,  as  the  ends  of  the  fibers  lie  in  con- 
tact, it  is  easy  to  understand  how  the  wave  of  contraction 
spreads.  Normally,  the  contraction  must  pass  from  about  the 
center  of  the  muscle-cell  where  the  nerve  terminates  in  the 
endtplate. 

CXhe  microscopic  changes  occurring  in  contracting  muscle 
are  not  well  understood.  The  living  muscle  of  a  beetle's  thigh 
when  placed  under  a  microscope  may  be  seen  in  contraction — a 
sight  of  the  most  striking  nature,  reminding  one  of  a  billowy, 
tempestuous  sea,  and  by  the  use  of  reagents  the  waves  of  co*n- 
traction  may  be  fixed. 

It  may  be  stated  that  the  parts  distinct  before  remain  so 


fUCTIOM. 

ring  the  con- 
ost  inappreci- 
m  about  ^i^ 
investigator, 
Bvers  may  be 
es  of  Marey's 
f  muscle,  and 
)  that  seen  in 

ises  along  the 
I  of  which  are 


ftraphic  tracing,  one 

wave-length  is 
ity  at  about  3 

B  of  mammals 
I  the  muscle  in 

(f  very  limited 
itraction  origi- 
>ting  a  similar 
bers  lie  in  con* 
of  contraction 
rom  about  the 
tninates  in  the 

racting  muscle 
a  beetle's  thigh 
contraction — a 
le  of  a  billowy, 
B  waves  of  co^n* 

if  ore  remain  so 


APPLICATIONS  OP  THE  GRAPHIC  METHOD.  187 

during  contraction,  and  that  all  parts  of  the  muscle-substance 
seem  to  share  in  the  changes  of  form  involved. 

The  Elasticity  op  Muscle. 

In  proportion  as  bodies  tend  to  resume  their  original  form 
when  altered  by  mechanical  force  are  they  elastic,  and  the  ex- 
tent  to  which  they  do  this  marks  the  limit  of 
their  elasticity. 

If  a  muscle  (best  one  with  bundles  of  fibers 
of  about  equal  length  and  parallel  arrange- 
ment) be  stretched  by  a  weight  attached  to 
one  end,  it  will,  on  removal  of  the  extending 
force,  return  to  its  original  length;  and  if  a 
series  of  weights  which  differ  by  a  common 
increment  be  applied  in  succession  and  the 
degrees  of  extensions  compared,  a^  may  be 
done  by  the  graphic  method,  it  will  be  appar- 
ent that  the  increase  in  the  extension  does  not 
exactly  correspond  with  the  increment  m  the 
weight,  but  is  proportionally  less.    With  an 
inorganic  body,  as  a  watch-spring,  this  is  not 

the  case.  ,      .^     *i. 

Further,  the  recoil  of  the  muscle  after  the 
removal  of  the  weight  is  not  perfect  fbr  all 
weights ;  but  within  certain  narrow  limits 
this  is  the  case,  i.  e.,  the  elasticity  of  muscle, 
though  slight  (for  it  is  easily  over-extended), 
is  perfect.  When  once  a  muscle  is  over-ex- 
tended, so  weighted  that  it  can  not  reach  its 
original  length  almost  at  once,  it  is  very  slow 
to  recover,  which  explains  the  well-known 
duration  of  the  effects  of  sprains,  no  doubt  ^     , 

owing  to  some  profound  molecular  change  r«.^iMj-D«^Boijjg^ 
associated  with  the  stretching.  -        Sufflin^^ 

The  tracings  below  show  at  a  glance  the  «^r  ito«|U«ajj 
difference  between  the  elasticity  of  muscle  |*t«i.«uo«««J»,5 
and  of  ordinary  bodies.  •!«» 

It  is  a  curious  fact  that  a  muscle  during 
the  act  of  contraction  is  more  extensible  than  when  pajs^ve ;  a 
dSLdvantage  from  a  purely  physical  point  of  view,  but  p^ba- 
bin  real  advantage  as  tending  to  obviate  spram  by  prevent- 
ing  too  sudden  an  application  of  the  extendmg  force. 


■; 


■    I 


miii»iiilmitt»:imiHt 


188 


AMIUAL  PHTSIOLOOT. 


It  will  be  borne  in  mind  that  the  Lmbs  are  held  together  as 
by  elastic  bands  slightly  on  the  stretch,  owing  to  the  elasticity 


I 


Fio.  16B.— niustratioiia  of  the  dlfferenoe  In  elMtldty  ot  loMiiinate  mud  Mrtag  matter  (kflar 
Yco).  1.  ShowB  gntphlMlly  bduiT]ar  of  a  eteel  Kpriac  nnder  equal  inerNiients  of  «>«glit. 
8.  A  similar  traciiiff  obtained  from  an  India-rubber  oand.  S.  The  lame  from  a  frmr'a 
muscle.  Note  that  Uie  ertenrtondflwreMM  with  egual  IncfMnents  of  weitfit,  and  that  the 
muscle  fldls  to  return  to  the  original  position  (absoHMa)  after  removal  of  the  wei^t. 

of  the  muscles.  Now,  as  seen  in  many  tracings  of  muscular 
contraction,  there  is  a  tendency  to  imperfect  relaxation  after 
contraction — the  contraction  remainder  or  elastic  after-effect, 
which  can  be  overcome  by  gentle  traction.  In  the  living  body, 
the  weight  of  the  limbs  and  the  action  of  the  stretched  muscles 
on  the  side  of  the  limb  opposite  to  that  on  which  the  muscles 
in  actual  contraction  aje  situated,  combine  to  make  the  action 
of  the  muscle  more  perfect  by  overcoming  this  tendency  to  im- 
perfect relaxation,  which  is  probably  less  marked,  independent 
of  these  considerations,  in  the  living  body.  This  elasticity  of 
living  muscles,  which  is  completely  lost  on  death,  is  a  fair 
measure  of  their  state  of  health  or  organic  perfection.  Hence 
that  hard  (elastic  recoil)  feeling  of  the  muscles  in  young  and 
vigorous  persons,  especially  athletes,  in  whom  muscle  is  brought 
to^e  highest  degree  of  perfection. 

(This  property  is  then  essentially  the  outcome  of  vitality, 
which  is  in  a  word  the  foundation  of  the  differences  noted  be- 
tween the  elasticity  of  inorganic  and  organic  bodies.  A  mus- 
cle, the  nutrition  of  which  is  suffering  from  whatever  cause, 
whether  deficient  blood-supply,  fatigue,  or  actual  difiease,  is 
deficient  in  elasticity.  We  wish  to  emphasize  these  relations, 
for  we  consider  it  very  impoi'tant  to  avoid  regarding  vital  phe- 
nomena in  the  light  of  physics  merely,  which  the  employment 
of  the  graphic  method  (and  indeed  all  methods  by  which  we  re> 
move  living  things  out  of  their  normal  relations)  fosters. 
lUelrieal  niMiMBtiia  of  Musi*.— Certain  pieces  of  apparatus 


imntKK'fmimMi' 


together  as 
lie  elasticity 


UviiiK  matter  (after 
Mrementa  of  v^ght. 
■ame  from  a  frag'a 

weight,  and  tint  the 
of  tSe  weight. 


s  of  muscular 
ilaxation  after 
tic  afler-effed, 
le  living  body, 
stched  muscles 
ah  the  muscles 
ake  the  action 
Bndency  to  im- 
d,  independent 
is  elasticity  of 
sath,  is  a  fair 
jction.  Hence 
in  young  and 
scle  is  brought 

oe  of  vitality, 
aces  noted  be- 
dims. A  mus- 
hatever  cause, 
aal  difiease,  is 
bese  relations, 
ling  vital  phe- 
e  employment 
f  which  we  re- 
fosters, 
of  apparatus 


APPLICATIONS  OF  THB  GRAPHIC  HBTHOD. 


189 


not  as  yet  referred  to  are  required  to  demonstrate  the  electrical 
condition  of  muscle.  The  gcdvcmometer  suitable  for  physio- 
logical experiments  is  one  having  very  many  coils  of  extreme- 
ly fine  wire,  and  so  adapted  to  indicate  the  presence  of  currents 
of  slight  intensity. 

In  order  that  it  may  be  ascertained  definitely  that  the  cur- 
rents that  deflect  the  galvanometer  needle  do  not  originate  out- 
side of  the  muscle  itself,  non-polari»dble  electrodes  very  care- 
fully made  must  be  used,  for  the  contact  of  ordinary  metallic 
electrodes  with  living  tissues  suffices  of  itself  to  generate  an 
electric  current,  as  may  be  simply  illustrated  to  one's  self  by 
placing  two  coins,  one  silver  and  the  other  copper,  in  contact 
with  the  upper  and  under  surfac-es  of  the  tongue  respectively, 
and  meeting  in  front;  a  peculiar  taste  results  fronl  the  current 
excited. 

The  construction  of  the  non-polarizable  electrodes  common- 
ly employed,  and  as  arranged  for  use,  is  diagrammatically  rep- 
resented below  (Fig.  186). 

Assuming  the  apparatus  for  the  detection  of  electrical  cur- 
rent in  muscle  to  be  in  working  order,  a  muscle  from  one  of 


Fio.  186.-Noii-polariiaUa  nhctrodw  of  Du  Boto-Rqrmond  (after  Rawothal).  At  c,  cli 
moliteaed  wiSiiaMae mHatkm, la  laid  on  atmOi  Gla«  ajrUiiiiler  a  la  lUled  with  i 
aolution  of  atne  NlpiMte,  a  good  ooodnetor,  bx  which  cnrraot  la  cooveyed  to  r  ~  ~ '  ~  ~ 
•iiio  plala  b,  and  tMuoe  to  fUvanometar. 


Up. 


the  cold-blooded  animals,  prepared  as  rapidly  and  carefully  as 
possible,  avoiding  all  contact  with  foreign  Wlies,  is  cut  across 
the  ends  transversely,  and  placed  on  pads  of  bibulous  paper 
moistened  with  physiological  ('60-70  per  cent)  saline  solution. 
The  uon-polarisable  electrodes  connected  with  the  galvanome- 
ter are  brought  in  contact  with  the  muscle.  What  results 
depends  on  the  parts  of  the  muscle  that  touch  the  electrodes, 
and  is  represented  diagramatically  in  Fig.  187. 

It  will  be  observed  that  the  diagram  indicates  that  between 
no  current  and  the  strongest  obtainable  there  are  all  shades  of 


^ 


190 


ANIMAL  PHTSIOLOGT. 


strength,  according  to  the  parts  of  the  muscle  connected  by  the 
electrodes.    The  strongest  is  that  resulting  when  the  superfi- 


'     Fio.  IflT    n<ipriiTiittHnn  nf  ninntrhwl  fnimintn  In  ■  miiifilii  rlinmtiiw  (■Itiir  ITnwinllnl) 

cial  equator  and  the  transverse  center  are  connected ;  and  it  is 
found  that  the  nearer  these  points  are  approached  the  stronger 
the  current  becomes,  as  is  indicated  by  the  greater  extent  of 
swing  of  the  galvanometer  needle.  In  connection  with  these  sur- 
prising  phenomena,  one  naturally  inquires  whether  such  a  mus- 
cle-curr'ent,  for  such  it  must  be,  is  natural  or  artificial.  Does 
such  exist  in  a  living  muscle  in  its  position  in  the  body,  or  has 
the  injury  done  to  a  muscle  in  its  preparation  by  section,  re- 
moval from  the  usual  conditions  of  nutrition,  and  such  like 
changes,  been  the  cause  of  the  current  ? 

After  much  investigation,  by  some  of  the  ablest  physiolo- 
gists of  the  day,  different  answers  are  returned  to  these  queries. 

Du  Bois-Reymond  maintains  that  such  currents  are  natural, 
and  may  be  obtained  from  muscle  contracting  in  situ  ;  while 
Hermann  and  others  believe  that  such  a  current  is  owing  to 
the  injury  done  by  the  section,  and  that  the  current  from  the 
equator  to  the  poles  of  the  section  is  due  to  the  fact  that  the 
injured  part  is  negative  to  the  uninjured  region. 

It  is  a  fact  that  if  the  current  be  led  off  from  an  exposed 
muscle  prior  to  section,  it  is  relatively  very  weak.  Further, 
the  electrode?  placed  on  the  uninjured  ventricle  of  an  animal's 


MMai 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


191 


nected  by  the 
1  the  superfi- 


•fterRoMBllMri). 

;ted ;  and  it  is 
d  the  stronger 
ater  extent  of 
with  these  sur- 
er such  a  mus- 
tificial.  Does 
le  body,  or  has 
by  section,  re- 
and  such  like 

blest  physiolo- 
9  these  queries, 
its  are  natural, 
in  sUu  ;  while 
nt  is  owing  to 
irrent  from  the 
le  fact  that  the 

om  an  exposed 
•eak.  Further, 
of  an  animal's 


heart  convey  no  current  to  the  galvanometer ;  but  aft«r  section, 
as  in  the  case  of  a  skeletal  muscle,  the  usual  result  follows. 
All  observers,  however,  are  agreed  that  a  current  is  produced 
during  contraction.  Those  not  believing  in  that  just  ref  eired 
to  above  ("current  of  rest"),  term  this  one  the  "currentof 
action  " ;  whUe  the  other  school  names  it  the  negatwe  vwnaiton 
of  the  current  of  rest,  inasmuch  as  the  galvanometer  needle 
swings  in  the  opposite  direction  indicating,  as  they  say,  a 
diminution  in  the  original  current.  ,       ..    * 

The  presence  of  this  undisputed  current  can  be  made  evident 
by  a  simple  experiment,  without  the  use  of  any  of  the  elabo- 
rate apparatus  noticed  above.    Let  two  frog's  Umbs,  with  the 


(ptter  BoMnUua). 

nerves  belonging  to  them,  be  prepared  in  ^  condition  and 
arranged  as  in  Fig.  188,  so  that  the  nerve  of  A  rests  along  the 
thigh  of  B.  On.stimulating  the  nerveof  Brthe  muscular  effect 
in  this  limb  is  answered  by  asimilaronein  A.  Thatthis  is  not 
necessarily  due  to  escape  of  the  current  upon  the  nerve  of  A, 
may  be  shown  by  putting  a  Ugature  around  the  nerve  of  B  below 
the  point  of  application  of  the  current  and  moistening  it  so  as 
to  allow  of  the  free  passage  of  the  current.  In  such  case  stimu- 
lation  of  the  nerve  of  B  gives  wholly  negative  results,  because 
the  ligature  has  destroyed  physiological  (molecular)  continuity, 
though  it  does  not  prevent  the  passage  of  the  current.    More- 


192 


ANIMAL  PHYSIOLOGY. 


:••     A 


over,  the  result  may  be  obtained  by  other  than  electrical 
stimuli. 

The  explanation  of  these  phenomena  of  the  "rheoscopic 
frog"  (physiological  rheoscope)  is  simply  that  the  electrical 
condition  of  B  has  been  suddenly  changed  by  the  passage  of 
the  current  into  the  nerve,  and  that  this  difference  of  electrical 
condition  (potential)  between  the  muscle  of  B  and  A's  nerve 
suffices  to  stimulate  the  muscle  of  A  (one  is  in  fact  -{-  and  the 
other  — ) ;  hence  the  stimulus  and  the  contraction,  the  nature 
of  which  in  A  is  the  same  as  that  in  B — ^i.  e.,  a  single  twitch 
in  B  gives  rise  to  the  same  in  A,  and  a  tetanic  contraction  to  a 
tetanic  contraction.  Plainly  the  contraction  of  A  must  be  due 
to  a  current  in  B,  hence  the  proof  that  a  current  actually  exists 
during  the  contraction  of  a  muscle.  It  may  be  noted  that  a 
mere  prick  of  B  will  arouse  in  it  a  contraction  which  is  fol- 
lowed by  the  same  result  as  before  in  A,  so  that  in  this  we  can 
exclude  the  original  stimulating  current  altogether  as  a  pos- 
sible source  of  fallacy,  as  stated  above.  But  one  of  the  most 
striking  proofs  that  there  is  a  current  of  action  (or  negative 
variation),  is  obtained  by  placing  the  nerve  of  such  a  prepara- 
tion as  that  represented  in  B  on  a  contracting  mammalian  heart ; 
with  each  systole  there  is  a  spasm  of  the  frog's  leg. 

It  is  important  to  note  that  the  electric  current  of  muscle, 
however  viewed,  is  an  event  of  the  latent  period.  It  is  asso- 
ciated with  the  chemical  and  all  the  other  molecular  changes 
of  which  the  actual  contraction  is  but  the  outward  and  visible 
sign ;  and  since  the  currents  of  rest  have  an  appreciable  dura- 
tion, wane  with  the  vitality  of  the  tissue,  and  wholly  disappear 
at  death,  they  must  be  associated  with  the  fundamental  facts 
of. organic  life;  for  it  is  to  be  remembered  that  electrical  cur- 
rents  are  not  confined  to  muscle,  but  have  been  detected  in  the 
developing  ^mbryo,  and  even  in  vegetable  protoplasm.  Though 
the  evidence  is  not  yet  complete,  it  seems  likely  |hatjlectjni£al 
phenomena  may  prove  to  be  associated  with  (we  designedly 
avoid  any  more  definite  expression)  atl  vital  phenomene^ 

Ohemisal  diMigM  in  Mvidi.— In  an  animal,  at'  a  variable 
period  after  death,  the  muscles  become  rigid,  producing  that 
stiffness  {rigor  mortis)  so  characteristic  of  a  recent  cadaver. 

The  subject  can  be  studied  in  some  of  its  aspects  to  great 
advantage  in  an  isolated  individual  muscle. 

Three  changes  in  a  muscle  that  has  passed  into  death  rigor 
are  constant  and  pronounced.  The  living  muscle,  either  alka- 
line or  neutral  in  reaction,  has  become  decidedly  acid;  an 


UMtM 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


198 


ham  electrical 

He  "rheoBcopic 
the  electrical 
the  passage  of 

ce  of  electrical 
and  A's  nerve 

act  +  and  the 

on,  the  nature 
single  twitch 
ontraction  to  a 
A  must  be  due 

actually  exists 
e  noted  that  a 
1  which  is  fol- 

in  this  we  can 
)ther  as  a  pos- 
ne  of  the  most 
m  (or  negative 
mch  a  prepara- 
nmalian  heart ; 

eg. 

rent  of  muscle, 
od.  It  is  asso- 
ecular  changes 
ard  and  visible 
preciable  dura- 
bolly  disappear 
damental  facts 
electrical  cur- 
detected  in  the 
klasm.  Though 
^  that  slectrii^ 
(we  designedly 

jnomenjkX 
at'  a  variable 
producing  that 
int  cadaver, 
ispects  to  great 

nto  death  rigor 
sle,  either  alka- 
dedly  acid;  an 


abundance  of  carbonic  anhydride  is  suddenly  given  off ;  and 
myosin,  a  sjiecific  proteid,  has  been  formed.  That  these  phe- 
nomena have  some  indissoluble  connection  with  each  other  so 
far  as  the  first  two  at  least  are  concerned,  while  not  absolutely 
certain,  seems  probable,  as  will  be  learned  shortly. 

It  will  be  borne  in  mind  that  muscle-fibers  are  tubes  con- 
taining semifluid  protoplasm,  and  that  a  coagulation  of  the 
latter  must  give  rise  to  general  rigor.  This  protoplasmic  sub- 
stance can  be  extracted  at  a  low  temperature  from  the  muscles 
of  the  frog,  and,  as  the  temperature  rises  coagulates  like  blood, 
giving  rise  to  a  clot  (myosin)  and  muscle-serum,  a  fluid  not 
very  unlike  the  serum  of  blood. 

This  myosin  can  also  be  extracted  from  dead  rigid  mus- 
cles by  ammonium  choride,  etc.  It  resembles  the  globulins 
generally,  but  is  less  soluble  in  saline  solutions  than  the  globu- 
lin of  blood  (paraglobulin) ;  is  less  tough  than  fibrin;  has  a 
very  low  coagulating  point  (55°  to  60°  C.) ;  and  is  somewhat 
jelly-like  in  appearance.  The  clotting  of  blood  and  of  muscle 
is  thus  analogous,  myosin  answering  to  fibrin,  and  there  being 
a  serum  in  each  case,  both  processes  marking  the  permanent 
disorganization  of  the  tissue.  The  reaction  seems  to  be  due  to 
the  formation  of  a  kind  of  lactic  acid,  probably  sarolactic; 
though  whether  due  to  excessive  production  of  this  acid,  on 
the  death  of  the  muscle,  which  for  some  reason  does  not  remain 
free  in  the  living  muscle,  or  whether  sarcolactic  acid  arises  as 
a  new  product,  is  uncertain.  It  is  certain  that  the  acid  reaction 
of  dead  muscle  is  not  owing  to  carbonic  acid,  for  the  reddened 
litmus  does  not  change  color  on  drying. 

That  a  muscle  in  action  does  use  up  oxygen  and  give  off 
carbonic  anhydride  can  be  definitely  proved;  though  it  is 
equally  clear  that  the  life  of  a  muscle  is  not  dependent  on  a 
eonatarU  supply  of  oxygen  as  is  that  of  the  individual,  for  a 
muscle  can  live,  even  contract  long  and  vigorously,  in  an  atmos- 
phere free  from  this  gas,  as  in  nitrogen. 

From  the  suddenness  of  the  increase  of  carbonic  anhydride, 
the  onset  of  death  and  rigor  morlia  has  been  compared  to  an 
explosion. 

QLf  ter  this  the  muscle  becomes  greatly  changed  physically : 
its  elasticity  and  translucency  are  lost;  there  is  absence  of 
muscle-currents ;  it  is  whoUy  unirritable,  is  less  extensible— it 
is,  as  before  stated,  firmer-Mt  is Jiead/ 

But  these  fundamental  j^enomena,  the  increase  of  carbonic 
anhydride  and  the  acid  reaction,  are  observable  after  prolonged 

IS 


wm^Mv^xmrnm 


194  ANIMAL  PHTSIOLOOT. 

tetanus.  It  was,  therefore— putting  all  the  facts  together  that 
we  now  refer  to  and  others,  not  forgetting  that  a  muscle  is 
always  respiring,  inhaling  oxygen,  and  exhaling  carbonic  an- 
hydride-T-not  unreasonable  to  conclude  that  normal  tetanus 
and  rigor  mortis  were  but  exaggerated  conditions  of  a  natural 
state.  The  coagulation  of  the  muscle  protoplasm  {plasma), 
gidng  rise  to  myosin,  was,  however,  a  serious  obstacle  to  the 
adoption  of  this  view.  But  it  has  very  recently  been  urged 
with  great  plausibility  that  an  old  view  is  correct,  viz.,  that 
rigor  mortis  (contracture)  is  the  last  act  of  muscle-life ;  it  is,  in 
fact,  a  prolonged  tetanus  or  contracture,  ending  in  most  cases, 
though  not  all,  in  coagulation  of  the  myosin.  This  state  can 
be  induced  and  recovered  from  in  favorable  cases  by  cutting 
off  the  blood  from  a  part  by  ligature,  and  later  readmitting  it 
to  the  starving  region.  It  has  been  suggested  that  the  prod- 
ucts of  the  muscle-waste,  usually  washed  away  by  the  blood- 
stream, in  such  an  experiment  and  after  death,  collect  and  act 
as  a  stimulant  to  the  muscle,  causing  it  to  remain  in  permanent 
contraction. 

The  other  constituents  of  dead  muscle  and  their  relative 
properties  may  be  learned  from  the  following  table  (Yon  Bibra) : 

Water.... 744*6 

Solids :  Myosin,  elastic  substance,  etc.,  in- 
soluble in  water. 156*4 

Soluble  proteids 19*3 

Gelatin.. 20*7 

.  Extractives  and  salts. 37*1 

Fats 23*0 

256  6—266*5 

Total.. 1,000 

Among  the  eoetractives  of  muscle  very  important  is  creatin 
('2  to  *3  per  cent),  a  nitrogenous  crystalline  body.  Certain 
allied  forms,  as  xanthin,  hypoxanthin  (sarkin),  kamin,  taurin 
and  uric  acid,  are  also  found. 

Glycogen  (animal  starch),  very  abundant  in  all  the  tissues, 
including  the  muscles  of  the  embryo,  is  found  in  small  quantity 
in  the  muscles  of  the  adult :  and  in  the  heart-muscle  a  peculiar 
sugar  (inosU)  is  present. 

It  is,  of  course,  very  difficult  to  say  to  what  extent  the  bodies 
known  as  extractives  exist  in  living  muscle,  though  that  glyco- 
gen, fats,  and  certain  salts  are  normally  present  admits  of  little 
doubt. 


ttwniP^ws'rwrsinwwtiT^W'rirf^^ 


APPLICATIONS  OF  TH£  GRAPHIC  METHOD. 


195 


together  that 
>t  a  muscle  is 

carbonic  an- 
>rmal  tetanus 
IS  of  a  natural 
ism  {plasma), 
bstacle  to  the 
7  been  urged 
rect,  viz.,  that 
e-life;  it  is,  in 
in  most  cases. 
This  state  can 
ses  by  catting 
readmitting  it 
that  the  prod- 
by  the  blood- 
;oIlect  and  act 
1  in  permanent 

their  relative 
le(VonBibra): 
.    744*6 

L56'4 
19'3 
20-7 
37-1 
23-0 

m  6—265*5 

1,000 

rtant  is  creatin 
body.  Certain 
,  kamin,  taurin 

all  the  tissues, 
small  quantity 
dscle  a  peculiar 

ctent  the  bodies 
igh  that  glyoo- 
admits  of  little 


There  is  a  coloring  matter  in  muscle,  more  abundant  in  the 
red  muscles  of  certain  animals  than  the  pale,  allied  to  heemo- 
globin,  if  not  identical  with  that  body. 

(It  may  be  stated  as  a  fact,  the  exact  significance  of  which 
is  unknown,  that  during  contraction  tb*^  extractives  soluble  in 
water  decrease,  while  those  soluble  in  a.     iol  increase. 

^t  will,  however,  be  very  plain,  from  what  has  been  stated 
in  this  section,  that  life  processes  and  chemical  changes  are 
closely  associated,  and  to  realize  this  is  worth  much  to  the 
student  of  Nature. 

Thermal  Changes  in  the  Contracting  Muscle. 

Since  very  marked  chemical  changes  accompany  muscular 
contraction,  it  might  be  expected  that  there  would  be  some 
modification  in  temperature,  and  probably  in  the  direction  of 
elevation.  Experiment  proves  this  to  be  the  case.  If  a  ther- 
mometer finely  graduated  be  kept  among  the  muscles  of  the 
limb  of  a  mammal  during  the  contractions  that  follow  the 
stimulation  of  the  main  nerve,  a  decided  rise  of  temperature 
may  be  noted  during  the  prolonged  tetanus  that  may  be  thus 
originated.  True,  during  the  contraction  of  a  set  of  muscles 
under  such  circumstances,  there  is  a  possible  fallacy,  from  the 
excess  of  blood  going  to  the  parts  owing  to  dilatation  of  the 
blood-vessels,  which  it  would  be  necessary  to  exclude — ^i.  e.,  we 
must  either  ascertain  that  such  does  not  take  place,  or  take  it 
into  account  as  a  factor  in  the  causation  of  the  rise  of  tempera- 
ture. However,  by  using  a  delicate  thermopyle,  a  muscle  to 
which  no  blood  passes  may  be  shown  to  grow  warmer  daring 
contraction. 

But  why  should  a  muscle  when  at  rest,  as  may  be  shown, 
maintain  a  certain  temperature,  unless  chemical  changes  are 
constantly  taking  place  P  As  already  stated,  such  is  the  case, 
and  the  rise  on  passing  into  tetanus  is  simply  an  expression  of 
increased  chemical  actionrv — 

What  is  the  nature  of  the  combustion  originating  this  heat  ? 
Are  certain  crude  materials  withdrawn  from  the  blood  and 
burned  up  directly  in  the  musole-substanoe ;  or  is  the  musclev 
itself  continuously  building  up  and  tearing  down  its  own  sub-( 
stance,  all  of  which  implies  oxidation  P-nt- 
/v  AH  attempts  to  explain  the  facts  apart  from  the  latter  view 
nave  been  unsuccessful,  and  we  are  forced  to  conclude  that 
such  is  the  sjmoptical  statement  of  the  life-history  of  muscle. 


MMMI 


HI[HWWI 


196 


ANIMAL  PHTSIOLOOT. 


No  machine  known  to  us  resembles  muscle  except  super- 
ficially. The  steam-engine  changes  fuel  into  heat  and  mechani- 
cal motion,  but  there  the  resemblance  ends.  Muscle  changes  > 
its  food,  or  fuel,  not  directly  into  either  heat  or  motion,  but  into) 
itself;  yet  as  a  machine  it  is  more  effective  than  thesteam-*, 
engine,  for  more  work  and  less  heat  are  the  outcome  of  its^ 
activity  than  is  the  case  with  the  steam-engine. 


The  Phtsioloot  of  Nbbvb. 

Muscle  and  nerve  are  constantly  associated  functionally,  and 
have  so  much  in  common  that  it  becomes  desirable  to  study 
them  together.  Much  that  has  been  established  for  muscle 
holds  equally  well  for  nerve ;  and  the  latter,  though  apparently 
wholly  different  in  structure  at  first  sight,  is  really  not  so. 
Nerve  has  its  protoplasmic  part  (axis-cylinder),  which  is  the 
essential  structure,  its  protective  sheaths,  and  its  nuclei  (nerve- 
corpuscles) 

As  already  indicated,  a  nerve  possesses  irritability,  and, 
since  a  muscle  does  not  respcy^d  to  an  electric  current  sent 

through  &  nerve  except  when  there  is  a 
sudden  change  in  the  strength  of  the 
current,  it  becomes  interesting  to  learn 
why  this  should  be  the  case. 

liVeriBMrtaL— In  Fig.  190  are  shown 
diagrammatically  two  muscle-nerve  prep- 
arations, and  the  apparatus  necessary 
for  applying  a  constant  current  and  a 
^(momentary)  induced  current  by  single 
shocks  to  the  nerva 

A  strength  of  current  sufficient  to 

cause  a  (sub-maximal)  contraction  by  an 

induction  shock  is  determined,  and  the 

induotorium  left  at  this  graduation.    A 

constant  current  of  moderate  strmgih  is 

allowed  to  pass  into  the  nerves  of  the 

preparation.    It  is  found  that,  in  the  one 

case,  the  muscle  contraction  is  increased, 

^^,«^  pSutaTMtw^  ""^^  "*  ****  other  diminished  or  absent, 

«q^^^  attend.  ""^  **  when   the  same  strength  of   induction 

shook  is  sent  into  the  nerve  at  the  points 

below  the  entrance  of  the  constant  currentr— that  is  to  say, 

the  irritability  of  the  nerve  has  been  increased  or  diminished. 


Flo.  IW.— IMagnuBMWtio  i«p- 
naentattoD  of  the  ntetiiod 
o(  tcatliig  tbe  adtablitty 
of  the  nerve  in  •HdrotamM 
(LwMloie).  rtwtthre  polee 
marked  ■«•,  negative,  -; 
theoontee  of  current  indi' 


irmi—>»i»MI 


mmm 


APPUCATIONS  OP  THE  OH    ('HIC     ^KTHOD. 


197 


except  saper- 
and  mechttni- 
uscle  changes  ^ 
otion,  but  into) 
lan  the  steam-, 
mtcome  of  its) 


nctionally,  and 
Table  to  study 
led  for  muscle 
iigh  apparently 
really  not  so. 
),  which  is  the 
B  nuclei  (nerve- 

■ritability,  and, 
ic  current  sent 
^hen  there  is  a 
trength  of  the 
resting  to  learn 
use. 

,  190  are  shown 
iscle-nerveprep- 
ratus  necessaky 
current  and  a 
irrent  by  single 

int  RuflBcient  to 
mtraction  by  an 
rmined,  and  the 
graduation.  A 
erate  strength  is 
)  nerves  of  the 
that,  in  the  one 
ion  is  increased, 
ished  or  absent, 
ih  of  induction 
rve  at  the  points 
—that  is  to  say, 
d  or  diminished. 


It  is  found  that  when  the  constant  (p'   iu-izuig)  (      rent  is  pass- 
ing from  above  downward — that  is,     t\en  the  <     liode  (n< na- 
tive pole)  is  on  the  side  toward  the  muscle — the  ii  rita  ili       f 
the  nerve  is  increased,  and  the  reverse  when  the  opposit         i 
ditions  prevail. 

^his  altered  condition  is  known  as  eledr<riomis.  I  or- 
tunately  this  term  is  used  somewhat  loosely,  sometimes  ,  ^m^ 
employed  in  the  sense  now  explained;  sometimes  to  denote 
a  change  of  electro-motive  force  that  accompanies  the  altera- 
tion of  irritability ;  and  again  to  cover  all  the  conditions  implied 
in  the  experiment.  It  is  a  fact  that  during  the  passage  of  a 
constant  current  the  natural  nerve-current  is  affected,  being 
increased  or  diminished  according  to  the  direction  of  the  polar- 
izing current.  There  is,  however,  so  much  difference  of  opinion 
in  regard  to  this  subject  that  it  is  very  doubtful  whether  it 
should  be  more  than  noticed  in  passing. 

But  to  return  to  electrotonus,  which  is  both  interesting  and 
important,  it  has  been  found  as  a  result  of  many  experiments 
that  profound  modifications  of  the  irritability  of  a  nerve  do 
take  place  during  the  passage  of  a  constant  current.  These  are 
diagrammatically  represented  in  Fig.  191. 


FlA.  11  ni«ti«iiiiiiillri  wprMwntatlon  of  TsrlaUoiN  In  elMtralonn*«oeordliiK  to  rtBMmth  of 
oomittemplofvd (after PflOaen.  i»n', •Motion of  mrre:  a. •iMMto('f  pole);  k, kathode 
1- pole).    Ooma  abovo  tlw  bortaoiitat  denote  lutdactratomia :  below,  the  opiMPdi^ 

Briefly  stated,  they  are  these:  1.  The  nature  of  the  change 
depends  on  the  direction  of  the  polarising  toonstant)  current ; 
hence,  if  the  current  is  descending,  there  is  an  increase  of  irri- 
tability ^caieleeirotonua)  in  the  portion  of  the  nerve  nearest  the 
muscle,  and  vice  versa.  2.  The  extent  of  the  change  of  irrita- 
bility is  dependent  on  the  strength  of  the  polarizing  current. 
3.  This  change  is  most  marked  dose  to  the  electrodes,  spreads 
to  a  considerable  extent  beyond  this  point  without  the  elec- 
trodes (extra-polar  regions),  and  also  exists  within  the  region 
of  contact  of  the  electrodes  (intra-polar  regions).    4.  It  follows 


I 


mUiA^MUmfr'lli 


198 


ANIMAL  PHYSIOLOGY. 


that  there  must  be  a  point  at  which  it  is  not  experienced  (indif- 
ferent point  or  neutral  point). 

Now,  it  is  possible  to  understand  why  a  sudden  change  in 
the  current  should  cause  a  muscular  contraction.  An  equally 
sudden  change,  a  profound  molecular  effect,  has  been  caused, 
and  this  we  must  believe  essential  to  the  causation  of  a  muscu- 
lar contraction  through  the  influence  of  a  nerve. 

'To  use  an  illustration  which  may  serve  a  good  purpose  if 
not  takon  too  literally,  it  is  a  well-known  experience  that  one 
sitting  in  a  room  in  which  a  clock  is  ticking  soon  fails  to  notice 
this  regular  sound ;  but  should  the  clock  stop  suddenly  or  as 
suddenly  commence  to  tick  very  rapidly,  the  attention  is 
aroused,  while  a  very  gradual  slowing  to  cessation  or  the  re- 
verse would  have  escaped  notice.  The  explanation  of  such 
facts  takes  us  down  to  the  very  foundations  of  biology ;  but 
just  now  we  wish  only  to  elucidate  by  our  own  experience 
how  it  is  possible  to  conceive  of  a  muscle  being  stimulated 
by  the  molecular  movements  of  nerve,  or  rather  a  change  in 
these. 

There  are  important  practical  aspects  to  this  question,  (^e 
may  understand  why  it  is  that  electricity  proves  so  rea^  a 
stimulus,  and  is  so  valuable  a  therapeutic  agent.     It  seems,! 
in  fact,  as  will  be  learned  later,  to  be  capable  of  taking  the> 
place  to  some  extent  of  that  constant  nerve  influence  which\ 
we  believe  is  being  exerted  in  the  higher  animals  toward( 
the  maintenance  of  the  regularity  of  their  cell-life  (metabol^ 
ism). 

Pathoiogiwl  and  GUniML-Ot  is  believed  that  in  the  nerves  of 
man,  within  his  living  body,  the  electrotonic  condition  can  be 
induced  as  in  an  isolated  piece  of  nerve.  Hence,  the  value  of 
the  constant  current  in  diminishing  nerve  irritability  in  neu- 
ralgia and  allied  conditions.  Apparatus  of  great  nicety  of  con- 
struction and  capable  of  generating,  accurately  measuring,  and 
conveniently  applying  electrical  currents  of  different  kinds, 
now  adds  to  the  resources  of  the  physician.  But  we  are  prob- 
ably  as  yet  only  on  the  threshold  of  electro-therapeutics. 

Law  of  OoatnetiMi  (IHiBlatiwi).— A  giveiTpiece  of  nerve  is 
stimulated  only  by  the  appearance  of  catelectrotonus,  and  the 
disappearance  of  anelectrotonus ;  but  the  disappearance  of  cat- 
electrotonus and  the  appearance  of  anelectrotonus  are  without 
effect  (Pflflger).  This  so-ctilled  law  is  supposed  to  explain  the 
following  facts,  which  may  be  thus  expressed  in  tabular  form 
(after  Landois) : 


wm 


ienced  (indif- 

en  change  in 

An  equally 

been  caused, 

n  of  a  muscu- 

od  purpose  if 
ence  that  one 

'ails  to  notice 
uddenly  or  as 
I  attention  is 
ion  or  the  re- 
ition  of  such 

biology;  but 
wn  experience 
Qg  stimulated 
Br  a  change  in 

luestion.  (^e 
res  so  rea^  a 
lut.  It  seems, 
of  taking  the 
nflnence  which 
dimals  toward( 
[•life  (metabol^ 

Q  the  nerves  of 
nditioncan  be 
;e,  the  value  of 
lability  in  neu- 
;  nicety  of  con- 
neasuring,  and 
ifferent  kinds, 
it  we  are  prob- 
kpeutics. 
jce  of  nerve  is 
•tonus,  and  the 
earance  of  cat- 
us  are  without 
to  explain  the 
I  tabular  form 


APPLICATIONS  OP  THB  GRAPHIC  MEl'HOD. 


199 


8TRBNOTH  OF  CURRBNT. 

AacnDiiia. 

PBaCINDINS. 

OnckMiDff. 

OnopvnlBg. 

On  elMing. 

On  opening. 

Weak 

C 
C 
R 

R 
C 
C 

C 
C 
C 

R 

Mecliam 

c 

Strong 

R 

R  =r  rest ;  C  =  contFution. 
BmMmI  OrgttM. — Electrical  properties  can  be  manifested 
by  a  large  number  of  fishes;  and  the  subject  is  of  special 
theoretical  interest.    It  is  now  established  that  the  development 
of  electrical  organs  points  to  their 
being  specially  modified  muscles 
— tissues,  in   fact,  in  wliich  the 
contractile  substance  has  disap- 
peared and  the  nervous  elements 
become  predominant  and  peculiar. 
No  work  is  done,  but  the  whole  of 
the  chemical  energy  is  represented 
by  electricity.     Functionally  an 
electric  organ  (which  usually  is 
some  form  of  cell,  on  the  walls  of 
which  nerves  are  distributed,  in- 
closing  a   gelatinous    substance, 
the  whole  being  very  suggestive 
of  a  galvanic  battery)  closely  re- 
sembles a  muscle-nerve  prepara- 
tion or  its  equivalent  in  the  nor- 
mal body.    The  electric  organs  ex- 
perience fatigue ;  have  a  latent 
period;  their  discharge  is  tetanic 
(interrupted)  ;  is  excited  by  me- 
chanical,   thermal,   or   electrical 
Htimuli;  and  the  effectiveness  of 
the  organs  is  heightened  by  elevation  of  temperature,  and  the 
reverse  by  cooling,  etc. 

-  '  '  Muscular  Work. 

If  during  a  given  period  one  of  two  persons  raises  a  weight 
through  the  same  height  but  twice  as  frequently  as  the  other, 
it  is  plain  that  he  does  twice  the  work ;  from  such  a  case  we 
may  deduce  the  rule  for  calculating  work,  viz.,  to  multiply  the 
weight  and  height  together. 


1M.-Tbe  eleetrie-fUh  torpedo,  dia- 
■ected  to  show  electric  uqwrBtw 
(Huxley),  b,  branchiee ;  c,  brain ;  e, 
dectric  organ;  g.  cranium;  me,  qiinal 
cord ;  h,  nerves  to  pectoral  flns ;  nl, 
nerri  laterales;  »p,  branches  of  pneu- 
mogaatrlo  nerves  to  electric  organs ; 
o,  eye. 


200 


ANIMAL  PHTSIOLOOT. 


The  effectiveness  of  a  given  muscle  must,  of  course,  depend 
on  the  degree  to  which  it  shortens,  which  is  from  one  hidf  to 
three  fifths  of  its  length ;  and  the  number  of  fibers  it  contains 
— i.  e.,  upon  its  length  and  the  area  of  its  cross-section,  taking 
into  account  in  connection  with  the  first  factor  the  arrange- 
ment of  the  fibers;  those  muscles  in  which  the  fibers  run 
longitudinally  being  capable  of  the  greatest  total  shortening. 

There  is,  as  shown  by  actual  experimental  trial,  a  relation 
between  the  work  done  and  the  load  to  be  lifted.  With  double 
the  weight  the  contraction  may  be  as  great  as  at  first,  or  even 
greater ;  but  a  limit  is  soon  reached  beyond  which  contraction 
is  impossible.  This  principle  may  be  stated  thus :  The  contrac- 
tion is  a  ftmction  of  the  stimtdua,  and  is  illustrated  by  the 
diagram  below  (Fig.  193). 


.<-r--i-rrT"nTTT-T-r-n-.- 

0     lanwMtfBouooMTOTSwniiio 


Fio.  181— OiagTMn  of  muKukur  contracUona  whh  wme  itimului  and  increMiiic  wetghu.  The 
DUmbera  reimwnt  gnmmM  (McKJendrick). 

It  has  been  shown  experimentally  that  the  chemical  inter- 
changes in  a  muscle,  acting  against  a  considerable  resistance, 
are  incrtosed — i.  e.,  the  metabolism  and  the  working  tension  are 
related. 

These  experimental  facts  harmonize  with  our  experience 
of  a  sense  of  satisfaction  and  effectiveness  in  the  use  of  the 
muscles  when  weights  are  held  in  the  hands;  and  it  must  be  a 
matter  of  practical  importance  that  each  person  should,  in 
taking,  systematic^ exercise,  keep  to  that  kind  j^ich^dpes  not 
ei|ber  overweight  or  underweight  the  musclM! 

Circumstances  influbnciko  the  Charactbb  of  Muscular 
AND  Nervous  Activity. 

Th«  InflvMM*  of  Blood4hipplj.  IMfW.— Fig.  194  shows  at  a 
glance  differences  in  the  curves  made  by  a  contracting  muscle 
suffering  from  increasing  fatigue. 

Suppose  that  in  such  a  case  the  blood  had  been  withheld 
from  the  muscle,  and  that  it  is  now  admitted,  an  almost  im- 
mediate effect  is  se^-n  in  the  nature  of  the  contractions ;  but 
even  if  only  saline  solution  had  been  sent  through  the  vessels 
of  the  muscle,  a  similar  change  would  have  been  noticeable. 
We  may  fairly  conclude  that  the  blood  and  saline  removed 
something  which  had  been  exercising  a  depressing  effect  on  the 


MHTM 


iirse,  depend 
one  half  to 
it  contains 
ition,  taking 
the  arrange- 
fibers  run 
hortening. 
il,  a  relation 
With  double 
irst,  or  even 
contraction 
The  contrac- 
rated  by  the 


T-T-1- 

www 

Hing  weight*.  The 


Lemical  inter- 
ile  resistance, 
g  tension  are 

tr  experience 
le  use  of  the 
it  must  be  a 
tn  should,  in 
lich  does  not 


>r  Muscular 

14  shows  at  a 
lOting  muscle 

teen  withheld 
0.  almost  im- 
raotions;  but 
;h  the  vessels 
n  noticeable, 
line  removed 
:  effect  on  the 


APPUCATIONS  OF  THE  GRAPHIC  METHOD. 


901 


vitality  of  the  muscle.    In  a  working  muscle,  like  all  living 
tissues,  there  are  products  of  vital  action  (metabolism)  that  are 


UODT. 


no.  iai-<!uiTeao(«miMdecaiitr«ctlaaiBdMereiit  itaseiaCfktisueiaftarToo).   A,c 

when  muade  waa  tmA ;  B,  C,  D,  E,  each  Juat  after  muade  had  already  contracted  two 
hundred  tinwa.  Thaaltanlioii  in  ieii|th  ol  iateiit  period  ia  not  wdferoacht  out  In  thaae 
tndnci. 

poisonous.  We  have  already  learned  that  a  working  muscle 
generates  an  excess  of  carbonic  anhydride,  and  something  which 
gives  it  an  acid  reaction ;  and  that  it  uses  up  oxygen  as  well  as 
other  matters  derivable  from  blood. 

(jVktigue  will  occur,  it  is  well  known,  if  the  muscles  are  used 
for  an  indefinitely  long  period,  no  matter  how  favorable  the 
blood-supply— another  evidence  that  there  is,  in  all  probability, 
some  chemical  product,  the  result  of  their  own  activity,  depress- 
ing them ;  and  this  is  rendered  all  the  more  likely  wh«i  it  is 
learned  that  the  injection  of  lactic  acid,  to  take  one  example, 
produces  effects  like  ordinary  fatigua 

It  is  also  a  matter  of  common  experience  that  exercise,  while 
beneficial  to  the  whole  body,  the  muscles  included,  as  shown  by 
their  enlargement  under  it,  becomes  injurious  when  carried  to 
the  point  of  fatigue. 

Why  the  use  of  the  muscles  is  conducive  to  their  welfare  is 
but  a  part  of  a  larger  question.  Why  does  the  use  of  any  tissue 
improve  it  ? 

(When  the  nerve  which  supplies  a  muscle  is  stimulated  its 
blood-vessels  dilate,  and  it  has  been  assumed  that  the  same 
happens  when  a  muscle  contracts  normally  in  the  body;  and 
when  muscular  action  is  increased  there  is  a  corresponding 
augmentation  in  the  quantity  of  blood  driven  through  the 
muscles  in  a  given  period,  even  if  there  be  no  actual  increase 
in  the  caliber  of  the  blood-vessels,  for  the  hettrt-beat  is  greatly 
accelerated. 

(]But  repose  is  as  necessary  as  exercise  for  the  greatest  effect- 
iveness of  the  muscles,  as  the  experience  of  all,  and  especially 
athletes,  proves. 

(That  the  nervous  system  plays  a  great  part  in  the  nutrition 
of  muscles  is  evident  from  the  fact,  among  countless  others, 
that  it  is  not  possible  to  use  the  bndn  to  its  greatest  capacity 
and  the  muscles  to  their  fullest  at  the  same  time ;  the  individuid 


UTMI 


i 
■1 


:i 


903 


ANIMAL  PHTSIOLOGT. 


engaged  in  physical "  training  "  must  forego  severe  mental  ap- 
plication. Nervous  energy  is  required  for  the  muscles,  and  all 
questions  of  blood-supply  are,  though  important,  subordinate. 
But  it  would  be  premature  to  enter  into  a  full  discussion  of  this 
interesting  topic  now. 

The  sense  of  fatigue  experienced  after  prolonged  muscular 
action  i^  complex,  though  there  can  be  no  doubt  that  the  nerve- 
centers  must  be  taken  into  account,  since  any  muscular  work 
that,  from  being  unusual,  requires  closer  attention  and  a  more 
direct  influence  of  the  will,  is  well  known  to  be  more  fatiguing. 
On  the  other  hand,  the  accumulation  of  products  of  fatigue 
doubtless  reports  itself  through  the  local  nervous  mechanism. 

Btpaxatim  of  Munto  from  tlis  Otatnl  ■trrow  Qjiltm.— When 
the  nerve  belonging  to  a  muscle  is  divided,  certain  histological 
changes  ensue,  which  may  be  briefly  described  as  fatty  degenera- 
tion, followed  by  absorption;  and  when  regeneration  of  the 
nerve-fibers  takes  place  on  apposition  of  the  cut  ends,  a  more 
or  less  complete  restoration  of  the  functions  of  the  nerve  fol- 
lows, but  the  exact  nature  of  the  process  of  repair  is  not  yet 
fully  agreed  upon ;  it  seems,  in  fact,  to  vary  in  different  caoes 
as  to  details,  though  it  is  likely  that,  in  instances  in  which 
there  is  a  complete  return  to  the  normal  functionally,  the  axis- 
cylinders,  at  all  events,  are  reproduced. 

The  degeneration  downward  is  complete ;  upward,  only  to 
the  first  node  of  Banvier. 

Immediately  after  the  section  the  irritability  of  the  nerve  is 
increased,  but  rapidly  disappears,  from  the  center  toward  the 
periphery  (Rittor-Valli  law). 

In  the  mean  time  the  muscle  has  been  suffering.  Its  irrita- 
bility at  first  diminishes,  then  becomes  greater  than  usual  to 
shocks  from  the  make  or  break  of  the  constant  current;  but 
finally  all  irritability  is  lost,  and  fatty  degeneration  and  disap- 
pearance of  true  muscular  structure  complete  the  history.  It 
is  theoretically  interesting,  as  well  aa  of  practical  importance, 
that  degeneration  may  be  delayed  by  the  use  of  th6  constant 
current,  the  significance  of  which  we  have  already  endeavored 
to  explain.  — ^ 

The  Inflatnas  of  Ttmpontuo.-- If  a  decapitated  frog  be  placed 
in  water  of  the  ordinary  temperature,  and  heat  be  gradually 
applied,  the  animal  does  not  move  (proving  that  the  spinal  cord 
alone  is  not  conscious),  but  the  muscles,  when  43°  to  60°  0.  is 
reached,  contract  and  become  rigid,  a  condition  known  as  "  heat- 
rigor."       N 


iryWMIr 


ire  mental  ap- 
aacles,  and  all 
subordinatp. 
iussion  of  this 

iged  mnscidar 

hat  the  nerve- 

anaoular  work 

on  and  a  more 

lore  fatiguing. 

iota  of  fatigue 

}  mechaniam. 

tjitok— When 

lin  histological 

fatty  degenera- 

leration  of  this 

it  ends,  a  more 

the  nerve  f ol- 

ipair  is  not  yet 

different  cases 

uices  in  which 

>nally,  the  axis- 

ipward,  only  to 

'  of  the  nerve  is 
iter  toward  the 

ing.  Its  irrita- 
r  than  usual  to 
at  current;  but 
ition  and  disap> 
the  history.  It 
oal  importance, 
of  th6  constant 
ady  endeavored 

1  frog  be  placed 
it  be  gradually 
;  the  spinal  cord 
I  43°  to  60°  0.  is 
cnownas"heat- 


APPLICATIONS  OP  THE  GRAPHIC  METHOD. 


ao8 


^Thert  are  some  advantages  in  investigating  changes  in  tem- 
perature by  the  graphic  method.  Curves  from  a  muscle-nerve 
preparation  show  that  elevation  of  temperature  shortens  the 
latent  period  and  the  curve  of  contraction.  Lowering  the  tem- 
perature has  an  effect  exactly  opposite,  as  might  be  supposed, 
and  these  changes  take  place  in  the  muscles  of  both  cold-blooded 
and  warm-blooded  animals,  though  more  marked  in  the  latter. 
The  modifications  evident  to  the  eye  are  accompanied  by 
others,  chemical  in  nature,  and  a  comparison  of  these  shows 
that  the  rapidity  and  force  of  the  muscular  contraction  run 
parallel  with  the  rapidity  and  extent  of  the  chemical  changes. 

(^Certain  drugs  also  modify  the  form  of  the  muscle-curve  very 
greatly,  so  that  it  appears  t]^at  the  molecular  action  which  un- 
derlies all  the  phenomena  of  muscle  and  nerve  (for  what  has 
been  said  of  muscle  applies  also  to  nerve,  if  we  substitute 
nervous  impulse  for  contraction)  can  go  on  only  within  those 
narrow  bounds  which,  one  realizes  more  and  more  in  the  study 
of  physiology,  are  set  to  the  activities  of  living  things. 

What  is  the  IntiMsts  Vatnrt  «f  Musalar  and  Mmrwou  Actioat— 
The  answers  to  these  questions,  to  which  some  allusion  has  been 
already  made,  are  by  no  means  certain.  Some  believe  that, 
since  the  nitrpgeneous  waste  of  the  body,  if  judged  by  the  urea 
of  the  urine,  is  not  augmented,  some  carbohydrate  breaks  up, 
which  would  be  in  accord  with  the  fact  that  the  gaseous  inter- 
change of  the  body  generally  is  increased  during  exercise,  espe- 
cially the  excretion  of  carbonic  anhydride. 

Upon  the  whole,  however,  such  a  view  does  not  harmonise 
well  with  the  behavior  of  protoplasm  generally,  and  it  is.  possi- 
ble to  conceive  of  other  processes  which  would  give  rise  to  car- 
bonic anhydride  and  additional  waste  products. 

( It  seems  to  be  likely  that  the  muscle  protoplasm  builds  up 

and  breaks  down  as  a  whole ;  that  this  is  constantly  going  on ; 

'  and  that  the  oxygen  which  is  stored  away  (intra-molecular) 

\  suffices  for  immediate  use;  but  that  when  %  contraction  takes 

I  place  all  the  chemical  procowoo  are  heightened,  so  that  we 

^  may  conceive  most  naturally  of  the  various  aspects  of  muscular 

life  as  phases  of  a  whole,  the  parte  of  which  are  closely  linked 

I  together. 

A  Another  unsettled  point  is  the  explanation  of  the  fact  that 

'a  nerve,  when  stimulated  nearer  the  nerve-center,  gives  rise  to  a 

more  marked  contraction,  with  the  same  stimulus  than  when 

excited  nearer  the  muscle. 

^me  suppose  that  the  change  that  in  a  nerve  constitutes  an 


ii  twaWiili'liijili  WUiltliti-ttKl-jiUt 


204 


ANIMAL  PHYSI0L007. 


impulse  gathers  force  as  it  proceeds — ^the  avalanche  theory  of 
Pflfiger ;  but  it  would  seem  more  natural  to  refer  this  effect  to 
the  jn^eater  irritability  of  the  nerve  nearer  the  centers. 

(The  chemistry  of  dead  nerves  throws  extremely  littld  light 
on  the  nature  of  nervous  processes.  The  latter  seem,  in  fact, 
to  be  accompaioed  by  chemical  changes  which  almost  ei^tirely 
elude  our  methods  of  detection  and  estimation.  Relatively  to 
the  chemical  the  dggtrical  phenomena  are  predominant;  ^ut 
nerve-forceis  not  electadcal  lorce,  nor  are  we  prepared  yet  to 
teach  that  iTlsthe  equivalent  df  that  or  nay  otiimtatwl^^a 
to  us.  '■ 

\j^e  fact  that  a  nerve  maintained  in  a  condition  approxi> 
mately  normal  may  be  stimulated  for  hours  without  exhaus- 
tion, has  led  some  to  adopt  the  tempting  conclusion  that  there 
are  no  invariable  chemical  accompaniments  of  nervous  excita- 
tion. But  in  this  and  all  other  instances  we  think  that  general 
principles  must  not  be  readily  set  aside  by  special  cases,  and 
we  should  ourselves  hesitate  to  adopt  any  opinion  so  contrary 
to  aU  that  is  known  of  organic  processes  as  this  theory  implies, 
except  on  the  amplest  and  clearest  evidence ;  and  we  lay  the 
more  stress  on  this,  because  we  think  it  is  a  sample  of  the  sort 
of  reasoning  that  is  apt  to  become  over-potent  with  those  that 
derive  their  conclusions  wholly  or  chiefly  from  laboratory  ex- 
periments, to  the  neglect  of  wider  observations,  which  put  the 
more  limited,  and  possibly  more  accurate,  ones  derived  from 
the  former  source,  in  a  truer  light,  and  enable  us  to  establish 
juster  relations. 

Unbtsipbd  Musclb. 

vThi»  form  of  muscular  tissue  is  JDharaoterised  by  its  long 
latent  period,  its  slow  wave  of  contraction,Jts  not  pasisintrmto 
tetanus,  and  the  progress  of  the  contraotionTCSbg  in  ei^er  a 
traSsverse  or  longitudinal  direction,  a  wave  of  contraction  in 
one  cell  being  capable  of  setting  itp  a  correspmiding  wave  in 
adjoining  cells  even  when  no  uerve-fibers  are  distributed  to 
them.    It  is  excited,  though  less  readily,  by  all  the  kinds  of 
stimuli  that  act  upon  striped  muscle.    In  the  higher  groups  of  A 
animals  this  tissue  is  chiefly  confined  to  the  viscera  of  the  / 
chest  and  abdomen,  constituting  in  the  case  of  some  of  them  ) 
thej^reater  part  of  the  whole  organ.  ^-^ 

^pie  slow  but  powerful  and  rhythmical  contraction  of  this 
form  of  muscle  adapts  it  well  to  the  part  such  organs  play  in 


'^^'^^mmfsw^si^mimammmsssmm 


iche  theory  of 
this  effect  to 

aters. 

aly  Uttle  light 
seem,  in  fact, 

hnost  eiTtirely 
Belatiyely  to 

ominant;  ^ut 

repared  yet  to 

r  fomTj^D^o. 

ition  approxi- 

thout  exhaos- 

sion  that  there 

lervons  excit«- 

ik  that  general 

icial  oases,  and 

on  so  contrary 

theory  implies, 

nd  we  lay  the 

iple  of  the  sort 

irith  those  that 

laboratory  ex* 

,  which  put  the 

I  derived  from 

us  to  establish 


Bed  by  its  long 
lot  pasising  into 
dug  in eiweFa 

contraction  in 
Midingwave  in 

distributed  to 

11  the  kinds  of 

igher  groups  of  >l 

viscera  of  the  / 

f  some  of  them  J 

traction  of  this 
L  organs  play  in 


APPLICATIONS  OF  THE  GRAPHIC  METTHOD. 


906 


the  economy.  There  are  variations,  however,  in  the  rapidity, 
force,  regularity,  and  other  qualities  of  the  contraction  in  dif- 
ferent parts:  thus,  it  is  comparatively  rapid  in  the  iris,  and  ex- 
tremely powerful  and  regular  in  the  uterus,  serving  to  produce 
that  prolonged  yet  intermittent  pressure  essential  under  the 
circumstances  (expulsion  of  the  foetus). 

Oompanttfiii — Muscular  contraction  is  relatively  sluggish 
and  prolonged  among  the  invertebrates,  to  which,  however,  the 
movement  of  the  wings  of  insects  is  a  marked  exception,  some 
of  them  having  been  shown  by  the  graphic  method  to  vibrate 
some  hundreds  of  times  in  a  second;   ' 

The  slow  movements  of  the  snail  are  proverbial.  As  a  rule, 
the  strength  of  the  muscles  of  the  invertebrates  is  incomparably 
greater  than  that  of  vertebrates,  as  witness  the  powerful  grasp 
of  a  crab's  claw  or  a  beetle's  jawsr~' 

These  facts  are  in  harmony  with  the  generally  slow  metab- 
olism of  most  invertebrates  and  the  lower  vertebrates. 

The  muscles  of  the  tortoise  contract  tardily  but  with  great 
power,  resist  fatigue  well,  retain  their  vitality  under  unfavor- 
able conditions,  and  after  death  for  a  very  long  period  (days). 

Without  resorting  to  elaborate  experiments,  the  student 
may  convince  himself  of  the  truth  of  most  of  the  above  state- 
ments by  observing  the  movements  of  a  water-snail  attached 
to  a  glass  vessel ;  the  note  made  by  the  bussing  of  an  insect, 
and  comparing  it  with  one  approaching  it  in  pitch  sounded  by 
some  instrument  of  music;  the  force  necessary  to  witiidraw 
the  foot  or  tail  of  a  tortoise ;  the  peristaltic  movements  of  the 
intestine  and  other  organs  in  a  freshly  killed  animal ;  or  the 
action  of  a  bee,  wasp,  or  wood-boring  beetle  on  the  cork  of  a 
bottle  in  which  one  of  them  may  be  inclosed. 

SPKOXAL  Ck>N8II>KBATION8. 

In  the  case  of  weakly  (phthisical)  persons  a  sharp  tap  on 
the  chest  will  often  produce  a  contraction  -of  the  muscles  thus 
stimulated ;  but,  in  addition,  a  local  contraction  lasting  some 
little  time,  known  as  a  wheai  or  idio-muscular  contraction,  fol- 
lows. This  phenomenon  seems  to  be  the  result  of  a  special 
irritability  in  such  muscles. 

^fomp  may  arise  under  a  great  variety  of  circumstances,^ 
but  it  seems  to  be  in  all  raset  either  a  complete  prolonged  tet»-/ 
nu8j.in  which  there  is  unusual  muscular  shortemng  in  severe) 
I,  aileast*  or  the  perristence  of  a  contraction  remainder.     / 


piiM-aiiMaialidiiifaU 


OTtiiriiilfilf 


206 


ANIMAL  PHTSIOLOOY. 


^The  great  differences  known  to  exist  between  individuals  6f 
the  same  species  in  strength,  endurance,  fleetness,  and  other 
particulars  in  which  the  muscles  are  concerned,  raise  numer- 
orxs  interesting  inquiries.  The  build  of  the  greyhound  or  race- 
horse suggests  in  itself  part  of  the  explanation  on  mechanical 
principles,  lung  capacity,  etc.  But  when  it  is  found  that  one 
dog,  horse,  deer,  or  man  excels  another  of  the  same  race  in 
swiftness  or  endurance,  and  there  is  nothing  in  the  form  to 
furnish  a  solution,  we  are  prompted  to  ask  whether  the  muscles 
may  not  contract  more  energetically,  experience  a  shortening 
of  the  latenc  period,  or  other  phase  of  contraction;  or  whether 
they  produce  less  of  waste-products  or  get  rid  of  them  more 
rapidly.  The  whole  subject  is  extremely  complicated,  and  we 
may  say  here  that  there  is  some  evidence  to  show  that  in  races 
of  dogs  and  other  animalp  which  surpass  their  fellows,  the 
nerve  regulating  the  heart  and  lungs  (vagus)  has  greater  power ; 
but,  leaving  this  and  much  more  out  of  the  account,  it  is  likely 
there  are  individual  differences  in  the  functional  nature  of  the 
muscle.  Of  equal  or  more  importance  is  the  energizing  influ- 
ence of  the  nervous  system,  which  probably  under  great  excite- 
ment (public  boat-races,  etc.)  acts  to  produce  in  man  those 
supermaximal  contractions  which  seem  to  leave  the  muscle 
long  the  worse  of  its  unusual  action.  The  nerve-centers,  it  is 
likely,  suffer  still  more  from  excessive  discharge  of  nerve-force 
(as  we  may  speak  of  it  lur  the  present)  necessary  to  originate 
the  muscular  work.  Hence  the  importance  of  training  to 
minimize  the  noKi-effective  expenditure,  ascertain  the  capacity 
possessed,  learn  the  direction  in  which  weaknesses  lie ;  and 
equally  important  the  muoh-negleoted  period  of  rest  before 
actual  contests— if  such  are  to  be  undertaken  at  all— lo  that 
all  the  activities  of  the  body  may  gather  head,  and  thus  be 
prepared  to  meet  the  unusual  demand  upon  them. 

iTJie  law  of  rhythm  in  organic  nature  is  beautifully  illus- 
trated by  the  behavior  of  nerve  and  especially  muscle ;  at  least 
it  is  more  obvious  in  the  case  of  muscle,  at  this  stage  of  oUr 
progress. 

(The  regularity  with  which  one  phase  succeeds  another  in  a 
single  contraction ;  the  essentially  rhythmic  (vibratory)  char- 
acter of  tetanus,  fatigue  and  recovery ;  the  recurrence  of  in- 
crease and  decrease  in  the  muscle  and  nerve  currents — ^in  fact, 
the  whole  history  of  muscle  is  ^a  admirable  commentary  on 
the  truth  of  the  law  of  rhythm,  into  which  in  further  detai? 
space  will  not  permit  us  to  enter. 


"•^MM 


•f 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


207 


individuals  6f 
38S,  and  other 
raise  numer- 
lound  or  race- 
on  mechanical 
ound  that  one 
same  race  in 
the  form  to 
er  the  muscles 
a  shortening 
»n ;  or  whether 
of  them  more 
icated,  and  we 
w  that  in  races 
ir  fellows,  the 
greater  power ; 
unt,  it  is  likely 
I  nature  of  the 
ergizing  influ- 
er  great  excite- 
in  man  those 
ive  the  muscle 
ve-centers,  it  is 
)  of  nerve-force 
iiry  to  originate 
of  training  to 
in  the  capacity 
lesses  lie;  and 
of  rest  before 
at  all— io  that 
d,  and  thus  be 
n. 

lautifuUy  illus- 
nnscle ;  at  least 
is  stage  of  otir 

ids  another  in  a 
ibratory)  char- 
surrenoe  of  in- 
rrents — ^in  fact, 
lommentary  on 
further  detail 


U[t  is  a  remarkable  fact  that  the  endurance  of  man,  especially 
civilized  man,  seems  to  be  greater  than  that  of  any  other  mam- 
mal. It  may  be  hazardous  to  express  a  dogmatic  opinion  as  to 
the  reason  of  this,  but  the  influence  of  thelmindjover  the  body 
w  unquestionably  greater  in  man  than  in  any  other  animal ; 
and,  if  we  are  correct  in  assigning  so  much  importance  to  the 
influence  of  the  tiervous  system  in  maintaining  the  proper 
molecular  balance  which  is  at  the  foimdation  of  the  highest 
good  of  an  organism,  we  certainly  think  that  it  is  in  this  direc- 
tion we  must  look  for  the  explanation  of  the  above-mentioned 
fact,  and  much  more  that  would  otherwise  be  obscure  in  man's 
functional  life. 

ToaetioBal  Variatirai, — We  have  endeavored,  in  treating  this 
subject  of  muscle,  to  point  out  how  the  phenomena  vary  with 
the  animal,  the  kind  of  muscle,  and  the  circumstances  under 
which  they  are  manifested.  It  may  be  shown  that  every  one 
of  the  qualities  which  a  muscle  possesses,  varies  with  the  tem- 
perature, the  blood-supply,  the  duration  of  its  action,  the  char- 
acter of  the  stimulus,  and  other  modifying  agents.  Not  only 
are  there  great  variations  for  different  groups  of  animals,  but 
lesser  ones  for  individuals ;  though  the  latter  are  made  more 
evident  indirectly  than  when  tested  by  the  usual  laboratory 
methods ;  but  tliey  must  be  taken  account  of  if  we  would  iu- 
derstand  animals  as  they  are.  Some  of  these  will  be  referred 
to  later. 

If  a  muscle-cell  be  regarded  in  the  aspect  that  we  are  now 
emphasizing,  its  study  will  tend  to  impr^  those  fundamental 
biological  laws,  the  comprehension  of  which  is  of  more  impor- 
tance than  the  acquisition  of  any  number  of  facts,  which,  how- 
evtsr  interesting,  can,  when  isolated,  profit  little. 

(Jfccperiment  has  not  done  much  directly,  and  it  seems  can 
not  at  present,  for  the  phjrsiology  of  man,  though  more  may  be 
accomplished  as  regards  muscle  and  nerve  than  some  other 
tissues.  It  is,  of  course,  possible  to  measure  the  rapidity  of 
the  passage  of  a  nervous  impulse  and  to  study  electrical  phe- 
nomena generally  to  some  extent.  Putting  all  that  is  known 
together,  it  would  appear  that,  without  referring  to  minor  dif- 
ferences which  unquestionably  exist,  the  muscle  and  nerve 
physiology  of  man  corresponds  pretty  closely  with  that  of  one 
of  the  highest  mammals,  and,  as  compared  with  the  lower  ver- 
tebrates, his  muscles  and  nerves  possess  an  irritability  of  a 
very  exalted  type,  with,  however,  a  corresponding  loss  or  dif- 
ference in  other  directions. 


mmmmmmm 


208 


ANIMAL  PHYSIOLOGY. 


Baamuy  of  fh«  Fhyiiology  of  Mvid*  and  V«rf«.— The  move- 
ments  of  a  muscle  are  distinguished  from  those  of  other  forms 
of  protoplasm  by  their  marked  definiteness  and  limitation. 

The  contraction  of  a  muscle-fiber  (cell)  results  in  an  increase 
in  its  short  transverse  diameter,  and  a  diminution  of  its  long 
diameter,  without  appreciable  change  in  its  total  bulk. 

Muscle  and  nerve  are  not  automatic,  but  are  irritable. 
Though  muscle  normally  receives  its  stimulus  through  a  nerve, 
it  possesses  independent  irritability. 

Stimuli  may  be  mechanical,  chemical,  thermal,  electrical,  and 
in  the  case  of  muscle,  nervous ;  and  to  be  effective  they  must 
be  applied  suddenly  and  last  for  a  brief  but  appreciable  time. 

Electrical  stimulation,  especially,  is  only  effective  when 
there  is  a  sudden  change  in  the  force  or  direction  of  the  cur- 
rents.   This  applies  to  both  muscle  and  nerve. 

A  muscular  contraction  consists  of  three  phases:  the  latent 
period,  the  period  of  rising,  and  the  period  of  falling  energy, 
or  of  contraction  and  relaxation. 

When  the  phase  of  relaxation  is  minimal  and  that  of  con- 
traction approaches  continuity,  a  tetanxis  results.  The  contrac- 
tions of  the  muscles  in  situ  are  tetanic,  and  are  accompanied 
by  a  low  sound,  evidence  in  itself  of  their  vibratory  character. 

The  prolonged  contraction  of  a  muscle  leads  to  fatigue; 
owing  in  part,  at  least,  to  the  accumulation  of  waste-products 
within  the  muscle  which  depress  its  energies. 

This  is  a  necessary  consequence  of  the  fact  that  all  proto- 
plasmic activity  is  accompanied  by  chemical  change,  and  that 
some  of  these  processes  result  in  the  formation  of  products 
which  are  hurtful  and  are  usually  rapidly  expelled. 

Muscular  contraction  is  accompanied  by  chemical  changes, 
in  which  the  formation  of  carbon  dioxide,  and  some  substance 
that  causes  an  acid  reaction  to  take  the  place  of  an  alkaline  or 
neutral  one.  Since  free  oxygen  is  not  required  for  the  act  of 
contraction,  but  is  still  used  up  by  a  contracting  muscle,  it  may 
be  assumed  that  the  oxygen  that  plays  a  part  in  actual  con- 
traction is  intra-molecular. 

Chemical  changes  are  inseparable  from  the  vital  processes 
of  all  protoplasm,  and  the  phenomena  of  muscle  show  that 
they  are  constantly  in  operation,  but  exalted  during  ordinary 
contraction  and  that  tetanic  condition  which  precedes  and 
may  end  in  coagulation  of  muscle  plasma  and  the  formation  of 
myosin.  The  latter  is  a  r^ult  of  the  disorganioation  of  muscle, 
and  has  points  of  resemblance  to  the  coagulation  of  the  blood. 


mfan 


APPLICATIONS  OF  THE  GRAPHIC  METHOD. 


909 


The  move- 
of  other  forms 
imitation. 

in  an  increase 
ion  of  its  long 
1  hnlk. 

are  irritable. 
m>ugh  a  nerve, 

,  electrical,  and 
stive  they  must 
reciable  time, 
effective  when 
ition  of  the  cur- 

ases:  the  latent 
falling  energy, 


knd  that  of  con- 
The  contrac- 
re  accompanied 
Ltory  character, 
iads  to  fatigue; 
waste'prodncts 

t  that  all  proto- 
hange,  and  that 
ion  of  products 
)lled. 

lemical  changes, 
some  substance 
>f  an  alkaline  or 
)d  for  the  act  of 
ig  muscle,  it  may 
"t  in  actual  oon- 

«  vital  processes 
nscle  show  that 
during  ordinary 
sh  precedes  and 
the  formation  of 
Eation  of  muscle, 
ion  of  the  blood. 


mm>: 


(The  contraction  of  a  muscle,  i^d  the  passage  of  a  nervous 
impulse,  ore  accompanied  by  electrical  changes.  Whether  cur- 
rents exist  in  uninjured  muscle  and  nerve  is  a  matter  of  con- 
troversy. All  physiologists  agree  that  they  exist  in  muscle 
(and  nerve)  during  functional  activity.  This  electrical  condi- 
tion Is  termed  the  "  negative  variation  "  by  those  believing  in 
currents  of  rest,  and  the  "  current  of  action  **  by  those  holding 
opposite  opinions.  The  current  is  of  momentary  duration,  and 
is  manifested  during  the  latent  period  of  muscle,  in  which  also 
the  chemical  changes  take  place ;  so  that  a  muscular  contrac- 
tion must  be  regarded  as  the  outcome  of  the  events  of  the 
latent  period,  which  is,  therefore,  though  the  shortest,  the  most 
important  of  the  phases  of  a  muscular  contraction. 

(j>uring  the  passage  of  a  constant  (polarizing)  cunent  from 
a  battery  through  a  nerve,  it  undergoes  a  change  in  its  irrita- 
bility and  shows  a  variation  in  the  electro-motive  force  of  the 
ordinary  nerve-current  (eleotrotonus).  This  fact  is  of  thera- 
peutic importance.  The  electrical  phenomena  of  nerve  are  alto- 
gether more  prominent  than  the  chemical,  iif»  reverse  of  which 
is  true  of  muscle.  The  activity  of  a  muscle  (and  nerve  proba- 
bly) is  accompanied  by  the  generation  of  heat,  an  exaltation  of 
which  takiss  place  during  muscular  contraction. 

Rigor  mortis  causes  an  increase  in  temperature  and  the 
chemical  interchanges  which  accompany  the  other  phenomena. 
A  muscle  may  also  become  rigid  by  passing  into  rigor  cdloria. 
Living  muscle  is  translucent,  alk^ine  or  neutral  in  reaction, 
and  elastic ;  dead  muscle,  opaque,  acid  in  reaction,  and  devoid 
of  elasticity,  but  firmer  than  living  muscle,  owing  to  coagula- 
tion of  the  muscle-plasma.  Dead  nerve  undergoes  similar 
changes. 

The  elasticity  of  muscle  is  restricted  but  perfect  within  its 
own  limits.  It  differs  from  that  of  inorganic  bodies  in  that  the 
increments  of  extension  are  not  directly  proportional  to  the  in- 
crements of  the  weight.  When  overstretched,  muscle  does  notr 
return  to  its  original  length  (loss  of  elasticity>,  hence  the  serious) 
nature  of  sprains. 

It  is  important  to  regard  muscular  elasticity  as  an  expres- 
sion of  vital  propertie& 

llie  work  done  by  a  muscle  is  ascertained  by  multiplying 
the  load  lifted  by  the  height;  and  the  capacity  of  an  individual 
muscle  will  vary  with  its  length,  the  arrangement  of  its  fibers, 
and  the  area  of  its  cross-section  (i.  e.,  on  the  number  of  fibers). 

The  work  done  may  be  regarded  as  a  function  of  the  resist- 

14 


j| 


■--1 


210 


ANIMAL  PHTSIOLOOT. 


ance  (load),  as  the  contraction  is  also  a  function  of  the  stimulus. 
The  separation  of  a  muscle  from  its  nerve  by  section  of  the  lat- 
ter leads  to  certain  changes,  most  rapid  in  the  nerve,  which 
show  that  the  two  are  so  related  that  prolonged  independent 
vitality  of  the  muscle  is  impossible,  and  make  it  highly  proba- 
ble that  muscle  is  constanUy  receiving  some  beneficial  stimulus 
from  nerve,  which  is  exalted  and  manifest  when  contraction 
takes  place. 

The  study  of  the  development  of  the  electrical  cells  of  cer- 
tain fishes  shows  that  they  are  greatly  modified  muscles  in 
which  contractility,  etc.,  has  been  exchanged  for  a  very  decided 
exaltation  of  electrical  properties.    It  is  likely,  though  not) 
demonstrated,  that  all  forms  of  protoplasm  undergo  electricals 
changes — ^that  these,  in  fact,  like  chemical  phenomena,  are  vital^ 
constants.  ^ 

The  phases  of  the  contraction  of  smooth  muscular  tissue  are 
all  of  longer  duration ;  the  contraction-wave  passes  in  different 
directions,  and  may  spread  into  celln  devoid  of  nerves,  which 
we  think  not  unlikely  also  to  be  the  case,  though  less  so,  for  all 
forms  of  muscle. 

The  smooth  muscle-cell  must  be  regarded  as  a  more  primi- 
tive, less  8peciali2sed,  form  of  tissue.  Variations  in  all  the  phe- 
nomena of  muscle  with  the  animal  and  the  circumstances  are 
clear  and  impressive.  Finally,  muscle  illustrates  an  evolution 
of  structure  and  function,  and  the  law  of  rhythm;^" 


THE  NEBY0U8  STBTESL-OENERAL  CONSIDERATIONS. 

Since  in  the  higher  vertebrates  the  nervous  system  is  domi- 
nant, regulating  apparently  every  process  in  the  organism,  it 
will  be  well  before  proceeding  further  to  treat  of  some  of  its 
functions  in  a  general  way  to  a  greater  extent  than  we  have  yet 
done. 

Manifestly  it  must  be  highly  important  that  an  animal  shall 
be  able  to  place  itself  so  in  relation  to  its  surroundings  that  it 
may  adapt  itself  to  them.  Prominent  among  these  adaptations 
are  certain  movements  by  which  food  is  secured  and  dangers 
avoided.  The  movements  having  a  central  origin,  a  peripheral 
mechanism  of  some  kind  must  exist  so  as  to  place  the  centers 
in  connection  with  the  outer  world.  Passing  by  the  evolution 
of  the  nervous  system  for  the  present,  it  is  found  that  in  verte- 
brates generally  there  is  externally  a  modification  of  the  epi- 


^IftlBllfMyjpJCtiiii 


n[iw«iiiisrnftiBiiiiiiii>iMitii 


THE  NKRVOUS  STSTEM— GENERAL  CONSIDERATIONS.     211 


the  stimulus, 
ion  of  the  lat- 
nerve,  which 
independent 
highly  proba- 
ficial  stimulus 
m  contraction 

al  cells  of  cer- 
ed  muscles  in 
a  very  decided 
7,  though  not> 
ergo  electrical< 
mena,areyiti^ 

Bular  tissue  are 

ises  in  different 

nerves,  which 

1  less  so,  for  all 

}  a  more  primi- 
I  in  all  the  phe- 
tmmstances  are 
es  an  evolution 
m/" 


IDERATIONS. 

system  is  domi- 
the  organism,  it 
it  of  some  of  its 
han  we  have  yet 

i  on  animal  shall 
'oundings  that  it 
hese  adaptations 
ired  and  dangers 
gin,  a  peripheral 
place  the  centers 
by  the  evolution 
md  that  in  verte- 
lation  of  the  epi- 


•iiMT'Tiiilinifflfllllltf"'' 


thelial  covering  of  the  body  {end-organ)  in  which  a  nerve  ter- 
minates, which  latter  may  be  traced  to  a  cell  or  cells  removed 
from  the  surface  {center),  and  from  which  in  most  cases  other 
nerves  proceed. 

(The  nervous  system,  we  may  remind  the  student,  consists  in 
vertebrates  of  icentem'in  which  nerve-cells  abound,  imited  by 
nerve-fibers  andlby  the  most  delicate  form  of  connective  tissue 
known,  in  connection  with  which  there  are  incased  strands  of 
protoplasm  or  nerves  as  outgrowths.  The  main  centers  are,  of 
course^  tggr^fated  ia  the  brain  and  spinal  cord^ 

It  is  possible  to  conceive  of  the  work  of  a  nervous  system 
carried  on  by  a  single  cell  and  an  afferent  and  efferent  nerve ; 
but  inasmuch  as  such  an  arrangement  would  imply  that  the 
central  cell  should  act  the  part  of  both  receiving  and  origi- 
nating impulses  (except  it  were  a  mere  conductor,  in  which  case 
there  would  be  no  advantage  whatever  in  the  existence  of  a  cell 
at  all),  according  to  the  principle  of  the  physiological  division 
of  labor,  we  might  expect  that  there  would  be  at  least  tjgp  cen- 
tral  cells— one  toreceive  and  the  other  to  transmit  impulses — 
oratleast  that  there  should  be  some  qiecialiaation  among  the 
central  cells;  and  we  shall  have  good  reason  later  to  believe 
that  this  has  reached  a  surprising  degree  in  the  highest  ani- 
mals. 

[Moreover^  it  would  be  a  great  advantage  if  the  termination 
of  the  ingoing  (afferent)  nerve  should  not  lie  exposed  on  the 
surface,  but  be  protected  by  some  form  of  cell  that  had  also  the 
power  to  transmit  to  it  the  impressions  received  from  without, 
in  a  form  suitable  to  the  nature  of  the  nerve  and  the  needs  of 
the^organism. 

[So  that  a  complete  mechanism  in  its  simplest  form  would 
f urmsh :  1.  A  peripheral  cell  or  nerve  end-organ.  3.  An  affer- 
ent or  sensory  nerve.  3.  Two  or  more  central  cells.  4.  An 
efferent  nerve,  usually  connected  with — 5.  A  muscle  or  other 
form  of  cell,  the  action  of  which  may  be  modified  by  the  out- 
going nerve,  or,  as  we  should  prefer  to  say,  by  the  central  nerv- 
ous cells  through  the  efferent  nerve.  The  advantages  of  the 
principal  cells  ^ing  within  and  protected  are  obvious. 

When,  then,  an  impression  made  on  the  peripheral  cell  is 
carried  inward,  there  modified,  and  results  in  an  outgoing  nerv- 
ous imptdse  answering  to  the  afferent  one,  giving  rise  to  a  mus- 
cular contraction  or  other  effect  not  confined  to  the  recipient 
cells,  the  process  is  termed  rejlesc  acHon.-^ 

(^The  great  size,  the  multiplicity  of  forms,  the  distinct  out- 


■'■* 
3f 


9ia 


ANIMAL  PHTSIOLOOT. 


r\ 


line  and  large  nuclei  of  nerve-cells,  suggest  the  probability 
that  they  play  a  very  important  part,  and  such  is  found  to  be 
the  case.  Indeed,  in  some  sense  the  rest  of  the  nervous  system 
may  be  said  to  exist  for  them. 

Probably  nerve-cells  do  sometimes  act  as  mere  conductors 
of  nervous  impulses  originating  elsewhere,  but  such  is  their 
lowest  function.  Accordingly,  it  is  found  that  the  nature  of 
any  reflex  action  depends  most  of  all  on  the  behavior  of  the 
central  cells. 

Clt  can  not  be  too  well  borne  in  mind  that  nerves  are  con- 
ductors and  such  only,    '^ey  never  originate  impulBes. 

The  properties  considered  in  the  last  chapter  are  common  to 
all  kinds  of  nerves  known ;  and  though  we  must  conceive  that 
there  are  some  differences  in  the  form  of  impulses,  these  are  to 
be  traced,  not  to  the  nerve  primarily,  but  to  the  organ  in  which 
it  ends  peripherally  or  to  the  central  cells. 

To  return  to  reflex  action,  it  is  found  that  the  muscular  re- 
sponse to  a  peripheral  irritation  varies  with  the  point  stimu- 
lated, the  intensity  of  the  stimulus,  etc.,  but  is,  above  all,  de- 
termined by  the  central  cells. 

Nerve  influence  may  be  considered  as  following  lines  of 
least  resistance,  and  there  is  much  evidence  to  show  that  an 
impulse  having  once  taken  a  certain  path,  it  ij  easier  for  it  to 
pass  in  this  direction  a  second  time,  so  that  we  have  the  founda- 
tion of  the  laws  of  habit  and  a  host  of  interesting  phenomena 
in  this  simple  principle. 

It  is  found  that,  in  a  frog  deprived  of  its  brain  and  sus- 
pended by  the  under  jaw,  there  is  no  movement  unless  some 
stimulus  be  applied ;  but  if  this  be  done  under  suitable  condi- 
tions, instructive  results  follow,  which  we  now  proceed  to  indi- 
cate briefly.  The  experiments  are  of  a  simple  character,  which 
any  student  may  carry  out  for  himself. 

S^niamtaL— Preparing  a  frog  by  cutting  off  the  whole 
of  the  upper  jaw  and  brain-case  after  momentary  ancesthesia, 
suspend  the  animal  by  the  lower  jaw  and  wait  till  it  is  perfect- 
ly quiet.  Add  to  water  in  a  beaker  sulphuric  acid  till  it  tastes 
distinctly  but  not  strongly  sour,  to  be  used  as  a  stimulus.  1. 
Apply  a  small  piece  of  bibulous  paper,  moistenoi  with  the  acid, 
to  the  iKier  part  of  the  thigh  of  the  animal.  The  leg  will  be 
drawn  up  and  the  paper  probably  removed.  Remove  the  paper 
and  cleanse  the  spot.  2.  Apply  a  similai^  piece  of  paper  to  the 
middle  of  the  abdomen ;  one  or  both  legs  will  probably  be 
drawn  up,  and  wipe  off  the  offending  body.    3.  Let  the  foot  of 


he  probability 
is  found  to  be 
lervous  system 

ere  conductors 

t  such  is  their 

the  nature  of 

>ehavior  of  the 

leryes  are  w)n- 

opnljses. 

are  common  to 

it  conceive  that 

ses,  these  are  to 

organ  in  which 

te  muscular  re- 
le  point  stimu- 
I,  above  all,  de- 

iowing  Imes  of 

0  show  that  an 
easier  for  it  to 
lave  the  f ouiida- 
ing  phenomena 

brain  and  sus- 
9nt  unless  some 

suitable  condi- 
proceed  to  indi- 
iharacter,  which 

U  off  the  whole 
tary  anesthesia, 
till  it  is  perfect- 
icid  till  it  tastes 

1  a  stimulus.  1. 
(3i  with  the  acid. 

The  leg  will  be 
lemove  the  paper 
)  of  paper  to  the 
ill  probably  be 
.  Let  the  foot  of 


THE  NERVOUS  8YSTBM-0ENERAL  CONSIDERATIONS.     218 
thefroff  hang  in  the  liquid;  after  a  few  moments  it  will  be 

will  be  drawn  up.  5.  Apply  stronger  acid  to  the  i°"d«  f  *^« 
right  thigh;  the  whole  frog  may  be  convulsed,  or  the  left  leg 
m!y  be  put  in  action  after  the  right.  Even  if  ^^^  ^t^^^J  "\K 
^^r  be  applied  near  the  anus,  it  will  be  removed  by  thft  hind- 
W  6^  Beneath  the  skin  of  the  back  (posterior  lymph-sac) 
inject  a  few  drops  of  liquor  strychnia  of  the  P^"?7^J^ 
after  a  few  minutes  apply  the  same  sort  of  stimulus  to  the 
thigh  as  before.     The  effects  follow  more  quickly  and  are 


IhmmammmouuaI 


WNMIIV  dNTM" 


'INHHrrailYOINTM 


AUTOatATNi 


/•IMOIIV  CIU.  «M0 

AmntNT  nhwi 


r  MOTOM  ecu.  ANO 
trnMNTMRM 


rMOTM  ecu  wrm 

imMNTMCIWC 


much  more  marked-the  animal,  it  may  be,  passing  intoa  gen- 

^'IC.t^ents  may  be  varied,  but  ^ce  to  es^li^ 
the  following  conclusions:  1.  The  stimulus  is  not  immediate- 
ly effective,  but  requires  to  act  for  a  certain  variable  period, 
depending  chiefly  on  the  condition  of  the  central  nervous  sys- 
tern  2.  The  movements  of  the  muscles  harmonize  (are  oo-ordi- 
nat^d),and  tend  to  accomplish  some  end-are  purposive,    if 


214 


ANIMAL  PHYSIOLOGY. 


the  nerve  alone  and  not  the  skin  be  stimulated,  there  may  be  a 
spasm  only  and  not  adaptive  movement.  3.  Nervous  impulses, 
when  very  abundant,  may  pass  along  unaccustomed  or  less  ac- 
customed paths  (experiment  4  and  6).  This  is  sometimes  spoken 
of  as  the  radiation  of  nervous  impulses. 

The  sixth  experiment  is  very  important,  for  it  shows  that 
the  result  varies  far  more  with  the  condition  of  the  nervous 
centers  (cells)  than  the  stimulus,  the  part  excited,  or  any  other 
factor. 

Antomatiiin. — But,  seeing  that  these  central  cells  have  such 
independence  and  controlling  power,  the  question  arises.  Are 
these,  or  are  there  any  such  cells,  capable  of  originating  im- 
pulses in  nerves  wholly  independent  of  any  stimulus  from 
without  ?  In  other  words,  have  the  nerve-centers  any  true 
automatism  ?  Apparently  this  quality  is  manifested  by  imi- 
cellular  organisms  of  the  rank  of  Amoeba.  Has  it  been  lost, 
or  has  it  become  a  special  characteristic  developed  to  a  high 
degree  in  nerve-cells  ? 

We  shall  present  the  facts  and  the  opinions  based  on  them 
as  held  by  the  majority  of  physiologists,  reserving  our  own 
criticisms  for  another  occasion :  1.  The  medulla  oblongata  is 
supposed  to  be  the  seat  of  numerous  small  groups  of  cells,  to  a 
large  extent  independent  of  each  other,  that  are  constantly 
sending  out  nervous  impulses  which,  pixxseeding  to  certain  sets 
of  muscles,  maintain  them  in  rhythmical  action.  One  of  the 
best  known  of  these  centers  is  the  respiratory.  3.  The  poste- 
rior lymph  hearts  of  the  frog  are  supplied  by  nerves  (tenth 
pair),  which  are  connected,  of  course,  with  the  spinal  cord. 
When  these  nerves  are  cut,  the  hearts  for  a  time  cease  to  beat, 
but  later  resume  their  action.  3.  The  heart  beats  after  all  its 
nerves  are  cut,  and  it  is  removed  from  the  body,  for  many  hours, 
in  cold-blooded  animals.  4.  The  contractions  of  the  intestine 
take  place  in  the  absence  of  food,  and  in  an  isolated  piece  of 
the  gut.  The  intestine,  it  will  be  remembered,  is  abundantly 
supplied  with  nerve-elements.  5.  In  a  portion  of  the  ureters, 
from  which  it  is  believed  nerve-cells  are  absent;  rhytlimical 
action  takes  place. 

Oondmioim— -1.  Whether  the  action  of  the  respiratory  aa 
similar  centers  could  contimie  in  the  absence  of  all  stimuli  can 
not  be  considered  as  determined.  2.  That  there  are  regular 
rhythmical  discharges  from  the  spinal  nerve-cells  along  the 
nerves  to  the  lymph  heartis  seems  also  doubtful.  3.  Later  in- 
vestigations render  the  automaticity  of  the  heart  more  unoer- 


? 


THE  NERVOUS  SYSTEM— GENERAL  CONSIDERATIONS.     216 


re  may  be  a 

rous  impulses, 

(med  or  less  ac- 

letimes  spoken 

it  shows  that 
of  the  nervous 
i,  or  any  other 

'cells  have  such 
on  arises.  Are 
)riginating  im> 
stimulus  from 
nters  any  true 
ifested  by  uni- 
%a  it  been  lost, 
oped  to  a  high 

based  on  them 
trying  our  own 
ia  oblongata  is 
ips  of  cells,  to  a 
are  constantly 
ar  to  certain  sets 
)n.    One  of  the 

3.  The  poste- 
f  nerves  (tenth 
be  spinal  cord. 
le  cease  to  beat, 
ats  after  all  its 
for  many  hours, 
>f  the  intestine 
olated  piece  of 
is  abundantly 
of  the  ureters, 
nt,-  rhythmical 


espiratory  an 
all  stimuli  can 
re  are  regular 
sells  along  the 
1.  3.  Later  in- 
't  more  unoer- 


J) 


tain  than  ever,  so  that  the  result  stated  above  (3)  must  not  be 
interpreted  too  rigidly. 

Similar  doubts  hang  about  the  other  cases  of  apparent  au- 
tomatism. 

As  regards  the  various  comparatively  isolated  collections  of 
cells  known  as  ganglia,  the  evidence,  so  far  as  it  goes,  is  against 
their  possessing  either  automatic  or  reflex  action;  and  new 
views  of  their  nature  will  be  presented  in  due  course. 

Herroui  InhiUtton.  —  If  the  pneumogastric  nerve  passing 
from  the  medulla  to  the  heart  of  vertebrates  be  divided  and 
the  lower  (peripheral)  end  stimulated,  a  decided  change  in  the 
action  of  the  heart  follows,  which  may  be  in  the  direction  of 
weakening  or  slowing,  or  positive  arrest  of  its  action. 

Assuming,  for  the  present,  that  the  cells  (center)  of  the  me- 
dulla have  the  power  to  bring  about  the  same  result,  it  is  seen 
that  such  nervous  influence  is  preyentijire  or  inhibitory  of  the 
normal  cardiac  beat,  so  that  the  vagus  is  tenned  an  inhibitory 
nerve.  Such  inhibition  plays  a  very  important  part  in  the 
economy  of  the  higher  animals,  as  will  become  more  and  more 
evident  as  we  proceed.  The  nature  of  the  influences  that  pro- 
duce such  remarkable  results  will  be  discussed  when  we  treat 
of  the  heart 

An  illustration  will  probably  serve  in  the  mean  time  to  make 
the  meaning  of  what  has  been  presented  in  this  chapter  more 
clear  and  readily  grasped. 

In  the  management  of  railroads  a  very  great  variety  of 
complicated  results  are  brought  about,  owing  to  system  and 
orderly  arrangement,  by  which  the  wishes  of  the  chief  mana- 
ger are  carried  out. 

Telegraphing  is  of  necessity  extensively  employed.  Sup- 
pose a  message  to  be  conveyed  from  one  office  to  another,  this 
may  (1)  simply  pass  through  an  intermediate  office,  without 
special  cognizance  from  the  operator  in  charge ;  (2)  the  operator 
may  receive  and  transmit  it  unaltered ;  (3)  he  may  be  required 
to  send  a  message  that  shall  vary  from  the  one  he  receives  in  a 
greater  or  less  degree ;  or  (4)  he  may  arrest  the  command  alto- 
gether, owing  to  the  facts  which  he  alone  knows  and  upon 
which  he  is  empowered  always  to  act  according  to  his  best  dis- 
cretion. 

(in  the  first  instance,  we  have  an  analogy  with  the  passage 
of  a  nervous  impulse  through  central  fibers,  or,  at  all  events, 
unaffected  by  cells ;  in  the  second,  the  resemblance  U  to  cells 
acting  as  conductors  merely ;  in  the  third,  to  the  usual  behavior 


»«fe»iiA*aik£(Mit>^.aKlW«i*!v,ii*^^ 


216 


ANIMAL  PHYSIOLOGY. 


of  the  cells  in  reflex  action ;  and,  in  tlie  fourth,  we  have  an  in- 
stance of  inhibition.  The  latter  may  also  be  rendered  clear  by 
the  case  of  a  horse  and  its  rider.  The  horse  is  controlled  by  the 
rider,  who  may  be  compared  to  the  center,  through  the  reins 
answering  to  the  nerves,  though  it  is  not  possible  for  either  rider 
or  reins  to  originate  the  movements  of  the  animal,  except  as 
they  may  be  stitnuli,  which  latter  are  only  effective  when  there 
are  suitable  conditions— when,  in  fact,  the  subject  is  irritable 
in  the  physiological  sense. 


'  THE  CIRCULATION  OF  THE  BLOODT^ 

Every  tissue,  every  cell,  requiring  constant  nourishment, 
some  means  must  necessarily  have  been  provided  for  the  con- 
veyance of  the  blood*  to  a^l  parts  of  the  organism.  We  now 
enter  upon  the  consideration  of  the  mechanisms  by  which  this 
is  accomplished  and  the  method  of  their  regulation. 

Let  us  consider  possible  mechanisms,  and  then  inquire  into 
their  defects  and  the  extent  to  which  they  are  found  embodied 
in  nature. 

Th«it  there  must  be  a  central  pump  of  some  kind  is  evident. 
Assume  that  it  is  one-chambered,  and  with  an  outflo-r  p^-ie 
which  is  continued  to  form  an  inflow-pipe.  This  might  'L'?>  , 
vided  with  valves  at  the  openings,  by  which  energy  woul 
saved  by  the  prevention  of  regurgitation.  In  such  a  syi  .  - 
things  must  go  from  bad  to  worse,  as  the  tissues,  by  constantly 
using  up  the  prepared  material  of  the  blood,  and  adding  to  it 
their  waste  products,  would  effect  their  own  gradual  starvation 
and  poisoning. 

It  might  be  conceived,  however,  that  waste  at  all  events  was 
got  rid  of  Vy  the  blood  being  conducted  through  some  elimi- 
nating organs ;  and  assume  that  one  such  at  least  is  set  aside 
for  respiratory  work.  If  the  blood  in  its  course  anjrwhere 
passed  through  such  organs,  the  end  would  be  attained  in  some 
degree ;  but  if  the  division  of  labor  were  coosiderabld,  we  should 
suppose  that,  gaseous  interchange  being  so  very  important  as 
we  have  been  led  to  see  from  the  study  of  the  chapters  on  gen- 
eral biology,  and  on  muscle,  organs  to  accomplish  this  work 
might  receive  the  blood  in  due  course  and  return  it  to  the  cen- 
tral pump  in  a  condition  eminently  fit  from  a  respiratory  point 

of  view. 

Such,  however,  would  neceBsarily  be  associated  with  a  more 


THE  CIBODLATION  OF  THE  BLOOD. 


217 


re  have  an  in- 
dered  clear  by 
itroUed  by  the 
ugh  the  reins 
'or  either  rider 
mal,  except  as 
ve  when  there 
ict  is  irritable 


:  nourishment, 
ed  for  the  con- 
ism.  We  now 
by  which  this 
ion. 

m  inquire  into 
rand  embodied 

dnd  is  evident, 
n  outflow  7^P© 
I  might  be  <  - 
lergywoul 
such  a  syi ;.  .. 
,  by  constantly 
nd  adding  to  it 
dual  starvation 

b  all  events  was 
gh  some  elimi> 
tast  is  set  aside 
iirse  anjrwhere 
;tained  in  some 
>tbld,  we  should 
y  important  as 
lapters  on  gen- 
lish  this  work 
a  it  to  the  oen- 
spiratory  point 

ad  with  a  more 


complicated  pump ;  and,  if  this  were  so  constructed  as  to  pre- 
vent the  mixture  of  blood  of  different  degrees  of  functional 
value,  higher  ends  would  be  attained. 

Turning  to  the  channels  themselves  in  which  the  blood 
flows,  a  IHtle  consideration  will  convince  one  that  rigid  tubes 
are  wholly  unfit  for  the  purpose.  Somewhere  in  the  courbe  of 
the  circulation  the  blood  must  flow  sufficiently  slowly,  and 
through  vessels  thin  enough  to  permit  of  that  interchange  be- 
tween the  blood  and  the  tissues,  through  the  medium  of  the 
lymph,  which  is  essential  from  every  point  of  view.  The  main 
vessels  must  have  a  strength  sufficient  to  resist  the  force  with 
which  the  blood  is  driven  into  them. 

Now,  it  is  possible  to  conceive  of  this  being  accomplished 
with  an  intermittent  flow ;  but  manifestly  it  would  be  a  great 
advantage,  from  a  nutritive  aspect,  that  the  flow  and  therefore 
the  supply  of  tissue  pabulum  be  constant.  With  a  pump  regu- 
larly intermittent  in  action,  provided  with  valves,  elastic  tubes 
having  a  resistance  in  them  somewhere  sufficient  to  keep  them 
constantly  over-distended,  and  a  collection  of  small  vesselt;  with 
walls  of  extreme  thinness,  in  which  the  blood-current  is  great- 
ly slackened,  a  steady  blood-flow  would  be  nudntained,  as  the 
student  may  readily  convince  himself,  by  a  few  experiments  of 
a  very  simple  kind : 

1.  To  show  the  difference  between  rigid  tubes  and  elastic 
ones,  let  a  piece  of  glass  rod,  drawn  out  at  one  end  to  a  small 
diameter,  have  attached  to  the  other  end  a  Higginson's  (two- 
bulb)  syringe,  communicating  with  a  vessel  containing  water. 
Every  time  the  bulb  is  squeezed,  water  f<  )W8  from  the  end  of 
the  glass  rod,  but  the  outflow  is  perfectly  intermittent. 

2.  On  the  other  hand,  with  a  long  elastic  tube  of  India-rub- 
ber, ending  in  a  piece  of  glass  rod  drawn  out  to  a  point  as  be- 
fore, if  the  action  of  the  pump  (bulb)  be  rapid  the  outflow  will 
be  continuous.  An  apparatus  that  every  practitioner  of  medi- 
cine requires  to  use  answers  perha|N9  still  better  to  illustrate 
these  and  other  principles  of  the  circulation,  such  as  the  pulse, 
the  influence  of  the  force  and  frequency  of  the  heart-beat  on  the 
blood-pressure,  etc.  We  refer  to  a  two-bulb  atomiser,  the  bulb 
nearer  the  outflow  serving  to  maintain  a  constant  air-pressure. 

We  may  now  examine  the  most  perfect  form  of  heart 
known,  that  of  the  mammal,  in  order  to  ascertain  how  far  it 
and  its  adjunct  tubes  answer  to  a  priori  expectations. 

Tha  IfaiiiiatiaB  BMuri— In  order  that  the  student  may  gain 
a  correct  and  thorough  knowledge  of  the  anatomy  of  the  heart 


218 


ANIMAL  PHT8IOL0OT. 


and  the  working  of  its  various  parts,  we  recommend  him  to 
pursue  some  such  course  as  the  following : 

1.  To  consult  a  number  of  plates,  such  as  are  usually  fur- 
nished in  works  on  anatomy,  in  order  to  ascertain  in  a  general 
way  the  relations  of  the  heart  to  other  organs,  and  to  the  chest 
wall,  as  well  as  to  become  familiar  with  its  own  structure. 

2.  To  supplement  this  with  reading  the  anatomical  descrip- 
tions, without  too  great  attention  to  details  at  first,  but  with 
the  object  of  getting  his  ideas  clear  so  far  as  they  go. 

3.  Then,  with  plates  and  descriptions  before  him,  to  examine 
several  dead  specimens  of  the  heart  of  the  sheep,  ox,  pig,  or 
other  mammal,  first  somewhat  generally,  then  systematicidly, 
with  the  purpose  of  getting  a  more  exact  knowledge  of  the 

various  structures  and 
their  anatomical  as  well 
as  physiological  relations. 

We  would  not  have 
the  student  confine  his 
attention  to  any  single 
form  of  heart,  for  each 
shows  some  one  structure 
better  than  the  others; 
and  the  additional  advan- 
tages of  comparison  are 
very  great.  The  heart  of 
the  ox,  from  its  sise,  is 
excellent  for  the  study  of 
valvular  action,  and  the 
framework  with  which 
the  muscles,  valves,  and 
vessels  are  connected; 
while  the  heart  of  the  ^ig 
(and  dog)  resemble  the 
human  organ  more  close- 
ly than  most  others  that 
can  be  obtained^ 

It  will  be  found  very 
helpful  to  perform  some 
of  the  dissections  under 
water,  and  by  the  use  of 
this  or  some  other  fluid 
the  action  of  the  valves 
may  be  learned  as  it  can 


no.  196.— The  left  auricle  wad  Tentriole  o|Miied  and 

f  Uielr  welle  removed  to  ibow  their  oantiee 

ThomaoB).    1,  rlRbt  jmlmoiiMT  vein  cut 

"  caWtjr  or  Mt  euricle;  |,  thick  imll  of 


■Mrt'of 
(Zleii 


■hort :  1'  caWtjr  oT  (rft  euricle ;  f,  thick  mUI  of 
left  ventricle:  4,  portion  o(  the  Mwae  with  papiUarr 
muacle  attached ;  S,  6',  the  other  papiUaiT  mua- 
clee ;  8,  one  eegment  of  the  mitral  valre ;  7,  in 
aorta  la  placed  over  the  wmihuar  valvaa. 


THE  CIBCULATION  OF  THE  BLOOD. 


Sltf 


nmend  him  to 

■e  usaally  fur- 
in  in  a  general 
nd  to  the  chest 

structure, 
omical  descrip- 

first,  but  with 
>ygo. 

lim,  to  examine 
leep,  ox,  pig,  or 
systematically, 
owledge  of  the 
structures  and 
tomical  as  well 
ogical  relations, 
ould  not  have 
nt  confine  his 
to  any  single 
heart,  for  each 
ne  one  structure 
Lan  the  others; 
dditional  ad  van- 
comparison  are 
A.  The  heart  of 
From  its  sice,  is 
for  the  study  of 
action,  and  the 
rk  with  which 
sles,  valves,  and 
are  connected; 
I  heart  of  the  ipig 
j)  resemble  the 
rgan  more  clocfe- 
nost  others  that 
»taihed» 

[1  be  found  very 
A)  perform  some 
iissections  under 
id  by  the  use  of 
lome  other  fluid 
m  of  the  valves 
earned  as  it  can 


in  no  other  way.  By  a  little  manipulation  the  heart  may  be  so 
held  that  water  may  be  poured  into  the  orifices,  prepared  by  a 
removal  of  a  portion  of  the  blood-vessels  or  the  auricles,  when 
the  valves  may  be  seen  closing  together,  and  thus  revealing 
their  action  in  a  way  which  no  verbal  or  pictorial  representa- 
tions can  do  at  all  adequately. 


-<" 


>aut< 


su:r 


i.f.i 


HtLl 


MMT 


V.r# 


Vm.  107.— View  of  Om  oriileM  of  tto  hawt  (Rm  briow,  the  whole  of  Om  vnitrielM  hairtng 
been  cut  ewagr  (after  Huxiqr).  KAV,  richt  •uricufe-Tentrleular  orlllce,  eumuiHled  by 
the thnw flan,  t.t).l,  t.v.t,  f. «. a, of  theVtoMpid  valve,  which «w ■tretehed br  weMita 
attached  to  tliftc*ordiBletul<iM«.  liir,  lettaiirieuk>-Teiitrieularorillae,ete.  i>i4,orUlce 
of  the  pulinonanr  aiterr.  the  lemlhiiiar  valvM  wipweHted  aa  havinc  mat  and  ekMed 
together.   .<10,  orifloe  of  the  aorta. 

A  heart  thoroughly  boiled  and  allowed  to  get  cold  shows, 
on  being  pulled  somewhat  apart,  the  course,  attachment,  and 
other  features  of  the  fibers  very  well,  as  also  the  skeleton  of 
the  organ,  which  may  be  readily  sepan»ted. 

When  this  has  all  been  done,  the  half  is  not  yet  accom- 
plished. A  visit  to  an  abattoir  will  now  repay  amply  for  the 
time  spent.  Animals  are  there  killed  and  eviscerated  so  rapidly 
that  an  observer  may  not  only  gain  a  good' practical  acquaint- 
ance with  the  relations  of  the  heart  to  other  parts,  but  may 
often  see  the  organ  still  living  and  exemplifying  that  action 
peculiar  to  it  as  it  gradually  approaches  quiescence  and  death 
—a  matter  of  the  utmost  importance. 

If  the  student  will  ther  compare  what  he  has  learned  of  the 
mammalian  heart  in  this  way  with  the  behavior  of  the  heart 
of  a  frog,  snake,  fish,  turtle,  or  other  animal  that  may  be  killed 
after  brief  ether  narcosis,  w^.thout  cessation  of  the  heart's  ao- 


220 


ANIMAL  PHYSIOLOGY. 


tion  he  will  have  a  broader  basis  for  his  cardiac  physiology 
than  is  usual ;  and  we  think  we  may  promise  the  medical  stu- 

dent,  who  will  in  tnis 
XA         ^.^ss^BSBs-^  and  other  ways  that 

may  occur  to  him 
supplement  the  usual 
work  on  the  human 
cadaver,  a  pleasure 
and  profit  in  the 
study  of  h«irt- dis- 
ease which  come  in 
no  other  way. 

With  the  view  of 
assisting  the  obser- 
vation of  the  student 
as  regards  the  heart 
of  the  mammal,  we 
would  call  special  at- 
tention to  the  follow- 
ing   points     among 
others:  Its  method  of 
on  the  left  pMt  or  i.^ K  «M.  ««».«-  »  — u-r-"»ui    Suspension,  chiefly  by 
^i&SS?«.'^2Sfw'»SS    its  Veat  vessels;  the 
•en**-  strong  fibrous  frame- 

work for  the  attachment  of  valves,  vessels,  ^f*!  ™^f?f- ^^^] 
the  great  complexity  of  the  arrangement  of  the  latter ;  the 
various  lengths,  mode  of  attachment,  and  the  strength  of  the 
inelastic  chordae  tendineie ;  the  papillary  muscles  which  doubt- 
less  act  at  the  moment  the  valves  flap  l>ack,  thus  preventang 
the  latter  l^eing  carried  too  far  toward  the  auricles,  the  pocket- 
ing  action  of  the  semilunar  valves,  with  their  strong  margin 
i^d  meeting  nodules  {corpora  aurarUii) ;  the  relative  thickness 
of  auricles  and  ventricles,  and  the  much  «^ter^cknes«  of 
the  walls  of  the  left  than  of  the  right  ventricle-difiEerences 
which  are  related  to  the  work  these  parts  perform. 

The  latter  may  be  well  seen  by  making  transverse  sections 
of  the  heart  of  an  animal,  especially  one  that  has  been  blea  to 
death,  which  specimen  also  shows  how  the  contraction  of  the 
heart  obliterates  the  ventricular  cavity. 

tt  ^11  also  be  well  worth  -'  ile  to  follow  up  the  course  of 
the  coronary  arteries,  noting  e,    ecially  their  point  of  origm. 

•Se  examination  of  the  valves  of  the  smaller  hearts  of  cold- 
bloodrLimals  is  a  matter  of  greater  difficulty  and  is  f  aoih- 


Huxley).    PA, pulmonMjr  artery,  wjjtt  «» Jjv^^!^ 


8 


THE  CIRCULATION  OP  THE  BLOOD. 


821 


iac  physiology 
le  medical  stu- 
vho  will  in  this 
bher  ways  that 
occur  to  him 
)ment  the  usual 
on  the  human 
er,  a  pleasure 
profit    in    the 

of  h«irt-dis- 
which  come  in 
ter  way. 
1th  the  view  of 
ling  the  obser- 
n  of  the  student 
igards  the  heart 
10  mammal,  we 
d  call  special  at- 
on  to  the  f oUow- 

points     among 
rs:  Its  method  of 
ension,  chiefly  by 
;reat  vessels;  the 
ig  fibrous  f  rame- 
od  muscle-fibers; 
I  the  latter;  the 
i  strength  of  the 
Bles  which  doubt- 
,  thus  preventing 
ricles,  the  pooket- 
(ir  strong  margin 
relative  thickness 
>ater  thickness  of 
fcricle— -dififerences 

fonp. 

ransverse  sections 
t  has  been  blea  to 
contraction  of  the 

JT  up  the  course  of 
point  of  origin. 
Her  hearts  of  cold- 
culty  and  is  facili- 


tated by  dissection  under  water  with  the  help  of  a  lens  or  dis- 
secting microscope;  but  even  without  these  instruments  much 
may  be  learned,  and  certainly  that  the  valves  are  relatively  to 
those  of  the  mammaUan  heart  imperfectly  developed,  will  be- 
come very  clear. 

ClBCULATION  OF  THE  BLOOD  IN  THE  MAMMAL. 

It  is  highly  important  and  quite  possible  in  studying  the 
circulation  to  form  a  series  of  mental  pictures  of  what  is  trans- 
piring    It  will  be  borne  in  mind  that  there  is  a  set  of  elastic 
tubes  of  relatively  thick  walls,  standing  open  when  cut  across, 
dividing  into  smaller  and  smaller  branches,  and  finally  ending 
in  vessels  of  more  thar-      ')web  fineness,  and  opening  out  into 
others,  that  become  u   <  <r  and  larger  and  fewer  and  fewer,  till 
they  are  gathered  up  into  two  of  great  sise  which  form  the  nght 
auricle.   The  larger  pipes  consist 
everywhere  of  elastic  tissue  prop- 
er, muscular  tissue  (itself  elas- 
tic), fibrous  tissue,  and  a  flat  epi- 
thelial lining,  so  smooth  that  the 
friction  therefrom  must  be  mini- 
mal as  the  blood  flows  over  it. 

The  return  tubes  or  veins  are 
like  the  arteries,  but  so  thin  that 
their  walls  fall  together  when  cut 
across.    They  are  different  from 
all  the  other  blood-tubes  in  that 
they  possess  valves  opening  to- 
ward the  heart  throughout  their 
course.    The  veins  are  at  least 
twice  as  numerous  as  the  arte- 
ries, and  their  capacity  many 
times  greater.   The  small  vessels 
or  capillaries  are  so  abundant 
and  wide-spread  that,  as  is  well 
known,  the   smallest  cut  any- 
where gives  rise  to  aflowof  blood, 
owing  to  section  of  some  of  these 
tubes,  which,  it  will  be  remem- 
bered, are  not  visible  to  the  un-  . 
aided  eye.     It  is  estimated  that  their  united  area  is  se-eral 
hundred  (600  to  800)  times  that  of  the  arteries. 


no.  190.-V«rtouf  I 


us  laren  of  Uw  w«ita„ot  » 
j|«iam(Likn9ols).  «« endothdluiii ; 
<  e  taitwiial  elMllc  tambw :  e.  m,  oircu- 
Lf'iSaar  flb£«  of  tlie  middle  oo«t ; 
c.  t.  oonnecthre  tiMue  of  the  outer  oo«t, 
orT.adTentttia. 


si^mi^'^sssmimB^i 


s»ssssr-jw»isti*f% 


222 


ANIMAL  PHYSIOLOGY. 


If  we  suppose  the  epithelial  Uning  pushed  out  of  a  small 
artery  we  have,  so  far  as  structure  alone  goes,  a  good  idea  of  a 
capillary-i.  e.,  its  Walls  are  but  one  cell  thick,  and  these  cells 


VW.  MOl 


Fio.  aoa-Vrin  with  Triw*  W««  <flP«  JWPS*. 
iSo  JM.-Velii  with  Ti^reB  ckiMMl,^  Wood  |wi 


FM.ain. 

Oil  by  a  hrtcnl  bnndi  bdow  (Diriton). 


though  long  are  extremely  thin,  so  that  it  is  quite  easy  to  im- 
derstond  how  it  is  that  the  amoeboid  corpuscles  can,  under  cer- 


-■h!f,=^lSSSJS^'^^5^ 


tain  circumstances,  push  their  way  through  its  probably  semi- 

^'''^mthat  has  been  said,  it  will  be  seen  that  the  whole  col- 
lection  of  vascular  tubes  may  be  compared  to  two  mverted  fun- 


it  the  whole  col 

wo  inverted  fun- 


to  Olwlrato  ike  ivIatHw  nranoitloM  oC  Um  •ansala 
iwrti  <li  fte  wchIt  tftUm  (aftw  Tee).    A,  Mrl»Tci>  m^O 


THB  CIBOULATION  OF  THB  BLOOD. 


388 


McMoiMd  are*  of  the 

■    ■   ijV.i 


nels  or  cones  with  the  smaller  end  toward  the  heart  and  the 
widest  portions  representing  the  capillaries. 


Thb  Action  or  ths  Mammalian  Hbast. 

Verjr  briefly  what  takes  place  may  be  thus  stated:  The 
right  auricle  contracting  squeeses  the  blood  through  the  au- 
riculo-ventricular  opening  into  the  right  ventricle,  never  quite 
emptying  itself  probably ;  immediately  after  the  right  ventricle 
contracts,  by  which  its  valves  are  brou^t  into  sudden  tension 
and  apposition,  thus  preventing  reflux  into  the  auricle ;  while 
the  blood  within  it  takes  the  path  of  least  resistance,  and  the 
only  one  open  to  it  '  ito  the  pulmonary  artery,  and  by  its 
branches  is  conveyed  to  the  capillaries  of  the  lungs,  from 
which  it  is  returned  freed  from  much  of  its  carbonic  anhy- 
dride and  replenished  with  oxygen,  to  the-left  auricle,  whence 
it  proceeds  in  a  similar  manner  into  the  great  arterial  main, 
the  aorta,  for  general  distribution  throughout  the  smaller 
arteries  and  the  capillaries  to  the  most  remote  as  w6ll  as  the 
nearest  parts,  from  which  it  is  gathered  up  by  the  veins  and 
returned  laden  with  many  impurities,  and  robbed  of  a  large 
proportion  of  its  useful  matters,  to  the  right  side  of  the  heart. 

It  will  be  remembered  that  corresponding  subdivisions  of 
each  side  of  the  heart  act  simultaneously,  and  that  any  decided 


i^sms^^ims^si 


'm^^^iummmmmKsmmmm 


9H 


ANIMAL  PHYSIOLOGY. 


departure  from  this  harmony  of  rhythm  would  lead  to  serious 
disturbance. 


Superior  VenftOav*. 


InferiqrVenfcCaTfc 


CapUUriMof  UTer. 
Portal  Vein. 


CanUIariMOftlie 
H)!ad,etc. 


FulmaMrr  Capn- 
luiM. 


Main  Arterial  Trunk. 


CapiUariesof 
Splanchnic  Area. 


CapOlariea  of  Trunk 
and  Lower  Ez- 
tremitiee.        , 


Sr  BdSl«2S^1S«^t  parta  <rf  the  ayatein  is  only  Tery  generally  I 


rindtoated. 


The  Vblocity  of  thk  Blood  and  Blood-Prbssueb.' 

If  the  relative  capacity  and  arrangement  of  the  various 
parts  of  the  circulatory  system  be  as  has  been  represented,  it 
follows  that  we  may  predict  with  some  confidence,  apart  from 
experiment,  what  the  speed  of  the  flow  and  the  vascular  ten- 
sion must  be  in  different  parts  of  the  course  of  the  circulataon^ 

We  should  suppose  that,  in  the  nature  of  the  case,  the  ye- 
locity  would  be  greatest  in  the  large  arteries,  gradually  dimin- 
Tu>  the  capillaries,  in  which  it  would  be  much  the  s  owest 
and,  getting  by  degrees  faster,  would  reach  a  speed  m  the  largest 
veins  approaching  that  of  the  corresponding  arteries. 


THE  CIRCULATION  OP  THE  BLOOD. 


225 


lead  to  serious 


lof  the 

.etc. 


'Cmta- 


KiUnAitertalTniiik. 


C* 


urilUuiMof 
Splanchnic . 


Area. 


CapUlariM  <rf  Tnink 
and  Lower  Ex- 
tremities. 


rtheUood.  Thoogfathe 
Illation  are  renreaented 
t  they  are  not  independ- 
wnUly  indicated. 


d-Pbbssube.' 

of  the  various 
n  represented,  it 
ence,  apart  from 
;he  vascular  ten- 
the  circulation, 
the  case,  the  ve- 
^adually  dimin- 
iich  the  slowest, 
ied  in  the  largest 
ieries. 


The  methods  of  determining  the  velocity  of  the  blood-stream 
have  not  entirely  surmounted  the  difficulties,  but  they  do  give 
results  in  harmony  with  the  above-noted  anticipations. 

The  area  of  the  great  aortic  trunk  being  so  much  less  than 
that  of  the  capillaries,  the  flow  in  that  vessel  we  should  expect  to 
be  very  much  swifter  than  in  the  arterioles  or  the  capillaries. 
Moreover,  there  must  be  a  great  difference  in  the  velocity  during 
cardiac  systole  and  diastole,  and  according  as  the  beat  of  the 
heart  is  forcible  or  otherwise.  But,  apart  from  these  more  ob- 
vious differences,  there  are  variations  depending  on  complex 
changes  in  the  peripheral  circulation,  owing  to  the  frequent 
variations  in  the  diameter  of  the  arterioles  in  different  parts, 
as  well  as  differences  in  the  resistance  offered  by  the  capillaries, 
the  causes  of  which  are  but  ill  understood,  though  less  obscure, 
we  think,  than  they  are  often  represented  to  be.  Since,  for  the 
maintenance  of  the  circulation,  the  quantity  of  blood  enter- 
ing and  leaving  the  heart  must  be  equal,  in  consequence  of  the 
sectional  area  of  the  great  veins  that  enter  the  heart  being 
greater  than  that  of  the  aorta,  it  follows  that  the  venous  flow 
even  at  its  quickest  is  necessarily  slower  than  the  arterial 

OompanitiT*. — There  must  be  great  variations  in  velocity  in 
different  animals,  as  such  measurements  as  have  been  made 
demonstrate.  Thus,  in  the  carotid  of  the  horse,  the  speed  of 
the  blood-current  is  calculated  as  about  306  mm.,  in  the  dog  at 
from  266  to  357  mm.  These  results  can  not  be  considered  as 
more  than  fair  approximations. 

Highly  important  is  it  to  note  that  the  rate  of  flow  in  the 
capillaries  of  all  animals  is  very  slow  indeed,  not  being  as  much 
as  1  mm.  in  a  second  in  the  larger  mammala  The  time  occu- 
pied by  the  circulation  is  also,  of  course,  variable,  being  as  a 
rule  shorter  the  smaller  the  animal.  As  the  result  of  a  niun- 
ber  of  calculations,  though  by  methods  that  are  more  or  less 
faulty,  the  following  law  may  be  laid  down  as  meeting  approxi- 
mately the  facts  so  far  as  warm-blooded  animals  are  concerned : 

The  circulation  is  effected  by  27  heart-beats;  thus,  for  a 
man  with  a  pulse  of  81,  the  time  occupied  in  the  completion  of 
the  course  of  the  blood  from  and  to  the  heart  would  be  H  =  3 ; 
i.  e.,  the  circulation  is  completed  three  times  in  one  minute,  or 
its  period  is  twenty  seconds ;  and  it  is  to  be  well  borne  in  mind 
that  by  far  the  greater  part  of  this  time  is  occupied  in  travers- 
ing the  capillariea 

15 


'ismmms^imi^kmammnfSe^vmmmMmamm.^mw'UmiiLMi  -uij'yik'i-'smimsisan^^siimm: 


226 


ANIMAL  PHTSIOLOOT. 


The  Circulation  undkr  thb  Microscope. 

There  are  few  pictures  more  instractive  and  impressive  than 
a  view  of  the  circulation  of  the  blood  under  the  microscope. 
It  is  well  to  have  similar  preparations,  one  under  a  low  power 
and  another  under  a  magnification  of  300  to  500  diameters.  With 
the  former  a  view  of  arterioles,  veins,  and  capillaries  may  be 


Fm.  Wl  rUMtlimiif  llw  will  lift  fl<n'if<iii<  M 1111111  iiiiilii  ■low  iiMtnirjIiii  iiimi'ii  riiinilin 
the  blood-TCMels.  and  in  one  oomer  the  pigment-spota  (after  Huri^).  a,  amau  arteriea 
(arteriolea):  «,  email  velaa.  Tba  mailer  Teeeela  are  the  caitOlarlw;,  Ite  coorae  at  the 
Mood  la  Indloated  by  arrowa. 

obtained  at  once.  Many  different  parts  of  animals,  may  be  used, 
as  the  web  of  the  frog's  foot,  its  tongue,  lung,  or  mesentery ; 
the  gill  or  tail  of  a  small  fish,  tadpole,  etc. 

The  relative  size  of  the  vessels ;  the  speed  of  the  blood-flow ; 
the  greater  velocity  of  the  central  part  of  the  stream ;  the  aggre- 
gation of  colorless  corpuscles  at  the  sides  of  the  vessels,  and  the 
occasional  passage  of  one  through  a  capillary  wall,  when  the 
exposure  has  lasted  some  time ;  the  crowding  of  the  red  cells ; 
their  plasticity;  the  small  size  of  some  of  the  capilleries,  barely 


THE  CIRCULATION  OP  THE  BLOOD. 


227 


lOPE. 

ipressive  than 
e  microscope. 
•  a  low  power 
meters.  With 
laries  may  be 


nltftiic  power,  ritowing 
g^^AjnwU  •rteriw 
icaT  The  couna  ot  the 

lals.maybeused, 
g, or  mesentery; 

•f  the  blood-flow; 
sream;theaggre- 
le  vessels,  and  the 
y  wall,  when  the 
:  of  the  red  cells; 
cutpille  ries,  barely 


allowing  the  corpuscles  to  be  squeezed  through ;  the  changes  m 
the  velocity  of  the  current,  especially  in  the  capillaries ;  its  pos- 
sible  arrest  or  retrocession;  the  velocity  in  one  so  much  greater 
than  iu  its  neighbor,  without  very  obvious  cause-all  this  and 
much  more  forms,  as  we  have  said,  a  remarkable  lesson  for  the 
thinking  student.  This,  like  all  microscopic  views,  especially 
if  motion  is  represented,  has  its  fallacies.    It  is  to  be  remem- 


itnae).    V,y*uu»tnir, 

■■■■jsxm  at  ■naUer  tw^^ 


•mpowdi 


Tut  UB.— Circulation  htthe  weboC  the  {roc's  toot  ^'■ 
thetta^SSSa  bTMchee  K  v,  v),  corned  w^  ^  « 
hi  dotted  o*er  idth  plgnent  BiMMit- 

bered  that  the  movements  are  all  magnified,  or  else  one  is  »pt 
to  suppose  the  capillary  circulation  extremely  rapid,  whereaa 
it  is  Uke  that  of  the  most  sluggish  part  of  a  stream,  and  very 
irr^ular. 

The  Chabacters  of  the  Blood-Flow. 

If  an  artery  be  opened,  the  blood  is  seen  to  flow  from  it  in 
a  constant  stream,  with  periodic  exaggerations,  which,  it  w 
found,  answer  to  the  heart-beats;  in  the  case  of  vents  and 
capillaries  the  flow  ;  -Iso  constant,  but  shows  none  of  the 
spurting  of  the  arte^ u?:  -tream,  nor  has  the  cardiac  beat  appar- 
ently  an  equal  modifying  effect  upon  it. 

We  have  already  explained  why  the  flow  should  be  constant, 
though  it  would  be  well  to  be  clearer  as  to  the  peripheral  re- 
sistance.   Tla  amount  of  frictioA  from  linings  co  smooth  as 


SlSSSSSSSSsSftSKs^S^Tt- 


L:..:iJJJ-USm! 


228 


ANIMAL  PHTSIOLOOT. 


those  of  the  blood-vessels  can  not  be  considerable.  Whence, 
then,  arises  that  friction  which  keeps  the  arterial  vessels  always 
distended  by  its  backward  influence  ?  The  microscopic  study 
of  the  circulation  helps  to  answer  this  question.  The  plas- 
ticity of  the  corpuscles  and  of  the  vessel  walls  themselves 
must  be  taken  into  account,  in  consequence  of  which  a  drag- 
ging influence  is  exerted  whenever  the  corpuscles  touch  the 
wall,  which  must  constantly  happen  with  vast  numbers  of 
them  in  the  smallest  vessels  and  especially  in  the  capillaries. 
The  arrangement  of  capillaries  into  a  mesh-work,  must  also,  in 
consequence  of  so  many  angles,  be  a  source  of  much  friction. 

The  action  of  the  corpuscles  on  one  another  may  be  com- 
pared to  a  crowd  of  people  hurrying  along  a  narrow  passage— 
the  obstruction  qomes  from  interaction  of  a  variety  of  forces, 
owing  to  the  crowd  itself  rather  than  the  nature  of  the  thor- 
oughfare. We  must  set  down  a  great  deal  to  the  influence  of 
the  corpuscles  on  one  another,  as  they  &i<3  carried  along,  accord- 
ing to  mechanical  principles ;  but,  as  we  shall  see  later,  other 
and  more  subtile  factors  play  a  part  in  the  capillary  circulation. 
Owing  to  the  peripheral  resistance  and  the  pumping  force  of 
the  heart,  the  arteries  become  distended,  so  that,  during  cardiac 
diastole,  their  recoil,  owing  to  the  closure  of  the  semilunar 
valves,  forces  on  the  blood  in  a  steady  stream.  It  follows,  then, 
that  the  main  force  of  the  heart  is  spent  in  distending  the 
arteries,  and  that  the  immediate  propelling  force  of  the  circu- 
lation is  the  elasticity  of  the  arteries  in  which  the  heart  stores 
up  the  energy  of  ite' systole  for  the  moment. 


Blood-Pbbssurb. 

Keeping  in  mind  our  schematic  representation  of  the  circu- 
lation, we  should  expect  that  the  blood  must  exercise  a  certain 
pressure  everywhere  throughout  the  vascular  system ;  that  this 
blood-pressure  would  be  highest  in  the  heart  itself ;  considera- 
ble in  the  whole  arterial  system,  though  gradually,  diminishing 
toward  thu  capillaries,  in  which  it  would  be  feeble ;  lower  still 
in  the  smaller  veins ;  and  at  its  minimum  where  the  great  veins 
enter  the  heart.  Actual  experiments  confirm  the  truth  of  these 
views ;  and,  as  the  subject  is  one  of  considerable  importance, 
we  shall  direct  attention  to  the  methods  of  estimating  and  re- 
cording an  animal's  blood-'pressure. 

First  of  all,  the  well-known  fact  that,  when  an  artery  is  cut, 
the  issuing  stream  spurts  a  certain  distance,  as  when  a  water- 


THE  CIRCULATION  OP  THE  BLOOD. 


229 


ble.    Whence, 
vessels  always 
'oscopic  study 
ion.    The  plas- 
Is  themselves 
which  a  drag- 
cles  touch  the 
numbers  of 
the  capillaries. 
z,  must  also,  in 
uch  friction, 
r  may  be  com- 
rrow  passage — 
riety  of  forces, 
le  of  the  thor- 
he  influence  of 
d  along,  accord- 
see  later,  other 
ary  circulation, 
mping  force  of 
,  during  cardiac 
the  semilunar 
It  follows,  then, 
distending  the 
'ce  of  the  circu- 
the  heart  stores 


on  of  the  circu- 
[ercise  a  certain 
^stem;  that  this 
»elf ;  considera- 
bly, diminishing 
dble ;  lower  still 
» the  great  veins 
le  truth  of  these 
kble  importance, 
imating  and  re- 

an  artery  is  cut, 
3  when  a  water- 


main,  fed  from  an  elevated  reservoir,  bursts,  or  a  'hydrant  is 
opened,  is  itself  a  proof  of  the  existence  of  blood-pressure,  and 
is  a  crude  measure  of  the  amount  of  the  pressure. 

One  of  the  simplest  and  most  impressive  ways  of  demon- 
strating blood-pressure  is  to  connect  the  carotid,  femoral,  or 
other  large  artery  of  an  animal  by  means  of  a  small  glass  tube 
(drawn  out  in  a  peculiar  manner  to  favor  insertion  an^  reten- 
tion by  ligature  in  the  vessel),  known  as  a  cannula,  by  rubber 
tubing,  with  a  long  glass  rod  of  bore  approaching  that  of  the 
artery  opened,  into  which  the  blood  is  allowed  to  flow  through 
the  above-mentioned  connections,  while  it  is  maintained  in  a 
vertical  position. 

To  prevent  the  rapid  coagulation  of  the  blood  in  such  ex- 
periments, it  is  customary  to  fill  the  cannula  and  other  tubes 
to  a  certain  extent,  at  least,  with  a  solution  of  some  salt  that 
tends  to  retard  coagulation,  such  as  sodium  carbonate  or  bicar- 
bonate, magnesium  sulphate,  etc.  If  other  connections  are 
made  in  a  similar  way  with  smaller  arteries  a&d  veins,  it  may 
be  seen  that  the  height  of  the  respective  columns,  represe^nting 
the  blood-pressure,  varies  in  each  and  in  accordance  with  ex- 
pectations. 

While  all  the  essential  facts  of  blood-pressure  and  many 
others  may  be  ilbistrated  by  the  above  simple  methods,  it  is 
inadequate  whe.i  exact  measurements  are  to  be  made  or  the 
results  to  be  recorded  for  permanent  preservation ;  hence  appa- 
ratus of  a  somewhat  elaborate  kind  has  been  devised  to  accom- 
plish these  purposes. 

The  graphic  methods  are  substantially  those  already  ex- 
plained in  connection  with  the  physiology  of  muscle;  but, 
since  it  is  often  desirable  to  maintain  blood-pressure  experi- 
ments for  a  considerable  time,  instead  of  a  single  cylinder,  a 
series  so  connected  as  to  provide  a  practically  endless  roll  of 
paper  (Fig.  308)  is  employed. 

When,  in  the  sort  of  experiments  referred  to  above,  the 
height  of  the  fluid  used  in  the  glass  tube  4o  prevent  coagula- 
tion just  suffices  to  prevent  outflow  from  the  artery  into  the 
connections,  we  have,  of  course,  in  this  a  measure  of  the  blood- 
pressure  ;  however,  it  is  convenient  in  most  instances  to  use 
mercury,  contained  in  a  glass  tube  bent  in  the  form  of  a  U,  for 
a  measure,  as  shown  in  the  subjoined  illustration.  It  is  also 
desirable,  in  order  to  prevent  outflow  of  the  blood  into  the 
apparatus,  to  get  up  a  pressure  in  the  U-tube  or  manometer  as 
near  as  may  be  equal  to  that  of  the  animal  to  be  employed  in 


HS»umR 


mammmmnam 


i80 


ANIMAL  PHYSIOLOGY. 


.1* 


riB.  wt.-k 


(•«?!:?:2*«fL»*»j?srs2: 


««.M*n.  mad  In  rnkUiiK  a  Mood-|ir«wii»  npwtnM"*  <*™*'™r2{iBmlBthem»- 


i>.uii.jii>:iii;<m<«Wwti"H""' 


iHtiiM 


THE  CIBCULATION  OF  THE  BLOOD. 


281 


bottle ;  ea,  the  oarotid,  in  wbidi  to  placed  the  cmiuU,  Mid  below  tbe  latter  a  foroepa,  whicb 
may  be  removed  when  the  Uood-preanre  to  to  be  actuailjr  meaaured.  The  regtofration  at 
the  height,  variation,  etc.,  of  Uood-preaaure,  to  beat  made  on  a  contimioua  roil  of  papw,  aa 
■eeninng  tOB. 

the  experiment.  This  may  be  effected  in  a  variety  of  ways, 
one  of  the  most  convenient  of  which  is  by  means  of  a  vessel 
containing  some  saturated  sodium  carbonate  or  similar  solu- 
tion in  connection  with  the  manometer. 

It  is  important  that  the  pressure  should  express  itself  as 
directly  and  truthfully  on  the  mercury  of  the  manometer  as 
possible,  hence  the  employment  of  a  tube  with  rigid  walls,  yet 
capable  of  being  bent  readily  in  different  directions  for  the  sake 
of  convenience. 

Mercury,  on  account  of  its  inertia,  is  not  free  from  objec- 
tion ;  and  when  very  delicate  variations  in  the  blood-pressure — 
e.  g.,  feeble  pulse-beats — are  to  be  indicated,  it  fails  to  express 
them,  in  which  case  other  fluids  may  be  employed. 


■to.  m.— Large  kymotraph,  with  oonttnwiua  iM  of  paper  (roatarl  The  olook-work  ma- 
ehiMtr  unrolto  the  paper  from  tbe  roU  O,  oaittaa  tt  amdoUilr  of«r  Oie  ojUndar  B,  and  then 
wtBda  it  up  into  Uw  roU  A.  Two  eleatro-mailnetio  marlcera  are  aeen  in  poaitton  feoording 
tnterv'^li  of  time  on  the  mortnr  roll  of  paper.  A  mawNMetar  mar  b"  Axed  in  any  oon- 
Tenient  poritlaii. 

It  will  be  noted  that  when  an  ordinary  cannula  is  used,  in- 
serted as  it  is  lengthvrise  into  the  blood-vessel,  the  pressure 
recorded  is  not  that  on  the  side  of  the  vessel  into  which  it  is 
inserted  as  when  a  H  -  piece  is  used,  but  of  the  vessel,  of  which 
the  one  in  question  is  a  branch.  The  blood-pressure,  in  the 
main  arterial  trunk  for  example,  must  depend  largely  on  the 
force  of  the  heart-beat ;  consequently  it  would  be  expected,  and  it 


^♦ife^^iiiBigsiMajwcMMiWfeiiawa^ 


282 


ANIMAL  PHYSIOLOGY. 


is  actually  found,  that  the  pressure  varies  for  different  animals, 
size  having,  of  course,  in  most  instances  a  relation  to  the  result. 
It  has  been  estimated  that  in  the  carotid  of  the  horse  the  arte- 
rial pressure  is  150  to  200  mm.  of  mercury,  of  the  dog  100  to  175, 
of  the  rabbit  60  to  90.  /ManVblood>pressure  is  not  known,  but 
is  probably  high,  we  may  suppose  not  less  thim  150  to  200  mm. 
After  the  fikct  that  there  is  a  certain  considerable  blood- 
pressure,  the  other  most  important  one  to  notice  is  that  this 
blood-pressure  is  constantly  varying  during  the  experiment, 
and,  as  we  shall  give  reason  to  believe,  in  the  normal  animal ; 
and  to  these  variations  and  their  causes  we  shall  presently  turn 
our  attention. 

THE  HEART. 

The  heart,  being  one  of  the  great  centers  of  life,  to  speak 
figuratively,  it  demands  an  unusually  close  study. 


•s 


The  Cardiac  Movkments. 

There  is  no  special  difficulty  in  ascertaining  the  outlines  of 
the  heart  by  means  of  percussion  on  either  the  dead  or  the 
living  subject,  Quite  otherwise  is  it  with  the  changes  in  form 
which  accompany  cardiac  action.  Attempts  have  been  made  to 
ascertain  the  alterations  in  position  of  the  heart  with  respect 
to  other  parjts,  and  especially  its  own  alterations  in  shape  dur- 
ing a  systole,  the  chest  being  unopened,  by  the  use  of  needles 
thrust  into  its  substance  through  the  thoracic  walls  ^  but  the 
results  have  proved  fallacious.  Again,  casts  have  been  made 
of  the  heart  after  death,  in  a  condition  of  moderate  extension, 
prior  to  rigor  mortis;  and  also  when  contracted  by  a  hardening 
fluid.  7^ese  methods,  like  all  others  as  yet  employed,  are  open 
to  serious  objections. 

Following  the  rapidly  beating  heart  of  the  mammal  with 
the  eye  produces  uncertainty  and  confusion  of  mind.  We  look 
to  instantaneous  photography  to  furnish  a  possible  way  out  of 
the  difficuttyT 

r  it  may  be  very  confidently  said  that  the  mode  of  contrac- 
tion of  the  hearts  of  different  groups  of  vertebrates  is  i^ariable^ 
though  it  seems  highly  probable  that  the  divergences  for  mam- 
mals are  slight.  The  most  that  can  be  certainly  afllrmed  of 
the  mammalian  heart  is,  that  during  contraction  of  the  ventri- 
cles they  become  more  conical ;  that  the  long  diameter  is  not 
appreciably  altered ;  that  the  antero  -  posterior  diameter  is 


iniliil  iKiii 


miiifaliliil'iri'i 


THE  CIRCULATION  OP  THE  BLOOD. 


288 


[erent  animals, 
to  the  result, 
lorse  the  arte- 
gr  100  to  176, 
|iot  known,  but 
to  200  mm. 
lerable  blood- 
Ice  is  that  this 
le  experiment, 
formal  animal ; 
presently  turn 


f  life,  to  speak 


the  outlines  of 
le  dead  or  the 
hanges  in  form 
e  been  made  to 
irt  with  respect 
s  in  shape  dur- 
)  use  of  needles 
walls  ^,  but  the 
ftve  been  made 
srate  extension, 
by  a  hardening 
>loyed,  are  open 

9  mammal  with 
aind.  We  look 
ible  way  out  of 

ode  of  contrao- 
»tes  is  i^ariable^ 
ences  for  mam- 
nly  aflHrmed  of 
a  of  the  ventri> 
diameter  is  not 
or  diameter  is 


lengthened ;  and  that  the  left  ventricle  at  least  turns  on  its  own 
axis  from  left  to  right.  This  latter  may  be  distinctly  made  out 
by  the  eye  in  watching  the  heart  in  the  opened  chest. 

The  Impulse  of  the  Heart. 

When  one  places  his  hand  over  the  region  of  the  heart  in 
man  and  other  mammals,  he  experiences  a  sense  of  pressure 
varying  with-the  part  touched,  and  from  moment  to  momep^ 
Instruments  constructed  to  convey  this  movement  to  recording 
levers  also  teach  that  certain  movements  of  the  chest  wall  cor- 
respond with  the  propagation  of  the  pulse,  and  therefore  to  the 
systole  of  the  heart.  It  can  be  recognized,  whether  the  hand 
or  an  instrument  be  used,  that  all  parts  of  the  chest  wall  over 
the  heart  are  not  equally  raised  at  the  one  instant.  If  the  beat- 
ing heart  be  held  in  the  hand,  it  will  be  noticed  that  during 
systole  there  is  a  sudden  hardening.  The  relation  of  the  apexi 
to  the  chest  wall  is  variable  for  different  mammals,  and  with  \ 
different  positions  of  the  body  in  man. 

^As  a  result  of  the  investigation  which  this  subject  ha^  re- 
ceived, i|i  may  be  inferred  that  the  sudden  tension  of  the  heart, 
owing  to  the  ventricle  contracting  over  its  fluid  contents,  causes 
in  those  cases  in  which  during  diastole  the  ventricle  lies  against 
the  chest  wall,  a  sense  of  pressure  beneath  the  hand,  which  is 
usually  accompanied  by  a  visible  movement  upward  in  some 
part  of  the  thoracic  wall,  and  downward  in  adjacent  parts. 
The  exact  characters  of  the  cardiac  impulse  are  very  variable 
with  different  human  subjects.  The  term  "  apex-beat "  is  fre- 
quently employed  instead  of  cardiac  impulse,  on  the  assump- 
tion that  the  apex  of  the  heart  is  brought  into  sudden  contact 
with  the  thoracic  walls  from  which  it  is  supposed  to  recede 
during  diastole.  But,  in  some  positions  of  the  body  at  all 
events  in  a  certain  proportion  of  cases,  the  apex  of  the  heart 
lies  against  the  chest  wall  during  diastole,  so  that  in  these 
instances  certainly  such  a  view  would  not  be  wholly  correct. 
But  we  would  not  deny  that  in  some  subjects  there  may  be  a 
genuine  knock  of  the  apex  against  the  walls  of  the  chest  during 
the  ventricular  systole. 

lit  will  not  be  forgotten  that  the  heart  lies  in  a  pericardial 

(sac,  moistened  with  a  small  quantity  of  albuminous  fluid ;  and 

that  by  this  sac  the  organ  is  tethered  to  the  walls  of  the  chest 

by  its  mediastinal  fastenings;  so  that  in  receding  from  the 

chest  wall  the  latter  may  be  drawn  after  it ;  though  this  might 


SinM««i.>^ii,iilj* 


eimulmi 


234 


ANIMAL  PHTSIOLOOT. 


also  follow  from  the  intercostal  muscles  being  simply  unsup- 
ported when  the  heart  recedes. 

Invbstioation  of  thb  Hkart-Beat  fbom  within. 

By  the  use  of  apparatus  introduced  within  the  heart  of  the 
mammal  and  reporting  those  changes  susceptible  of  graphic 
record,  certain  tracings  have  been  obtained  about  the  details  of 


Fio.  int.— Marey't  oardiao  MMUid  wiiieh  mar  ba  UMid  to  asplan  the  diainben  at  Urn  haait 
(aftei  Foater).  a,  ia  made  of  rubber  aireldied  over  a  wire  framework,  with  metallic 
■npporta  above  and  below ;  b,  la  a  long  tube. 

which  here  are  uncertainty  and  disagreement,  though  they 
seem  to  establish  the  nature  of  the  main  features  of  the  cardiac 
beat  clearly  enough.    An  interpretation  of  such  tracings  in  the 


Bight  aurtole. 


Bight  Tentarlcto. 


Cardiac  impiilae. 


Fta.  WO.— Slmultaneotia  tradnga  from  the  interior  of  the  right  auricle,  from  the  Interior  of  the 
right  tentrlde,  and  of  the  oardiao  impute,  in  the  hone  (after  Obauveau  and  Marejr). 
Tracinga  to  be  read  from  left  to  right,  and  the  ref erenoea  abora  are  in  the  order  from  wn 
to  bottom.  A  completo  cardiac  cycle  la  included  between  the  thick  TerUeal  Unea  I  and  u. 
The  thin  vertical  Itnea  indicate  tenoia  of  a  aeoond.  The  gradual  riae  of  nreaMire  within  the 
Tentrlcle  (middle  tnudng)  during  diaat«de,  the  auddeo  riae  with  the  mtoie,  ita  nalntenanoe 
with  oacillationa  for  an  apiMveiable  time,  it*  aoddan  Call,  eto.,  are  all  well  ahown.  Tberaia 
diiagraement  aa  to  the  exact  meaning  of  the  minor  ourraa  In  the  larger  onea. 

light  of  our  general  and  special  knowledge  warrants  the  fol- 
lowing statement. 


w^'«'<>iW^»W'>'^',wi.»iaiii<tfiAiiiiaBii<CTi(rtwMiiiii'(>i 


iMMP 


THE  GIBCULATION  OF  THE  BLOOD. 


985 


I  simply  unsup- 


WITHIN. 

le  heart  of  the 
lible  of  graphic 
it  the  details  of 


dumben  oC  the  hewt. 
mework,  with  metallic 


1.  Both  auricular  and  ventricular  systole  are  sudden,  but 
the  latter  is  of  very  much  greater  duration. 

2.  While  the  chest  wall  feels  the  ventricular  systole,  the  au- 
riculo-ventricular  valves  shield  the  auricle  from  its  shock. 

3.  During  diastole  in  both  chambers  the  pressure  rises 
gradually  from  the  inflow  of  blood ;  and  the  auricular  contrac- 
tion produces  a  brief,  decided,  though  but  slight  rise  of  press- 
ure in  the  ventricles. 

4.  The  onset  of  the  ventricular  systole  is  rapid,  its  maximum 
pressure  suddenly  reached,  and  its  duration  considerable. 

The  relations  of  these  various  events,  their  duration,  and  the 
corresponding  movements  of  the  chest  wall,  may  be  learned  by 
a  study  of  the  above  tracing  which  the  student  will  find  worthy 
of  his  close  attention. 


it,  though  they 
as  of  the  cardiac 
I  tracings  in  the 


V 


BVtwiriole. 


Bight  rentricle. 


OirdlM  impulM. 


,  from  the  interior  of  the 
ChauTceu  Mid  Meresr). 
i«  in  the  order  from  top 
dr  Tertieal  Itnce  I  and  n. 
M  of  srcMure  within  the 
mtifle,  lie  mninteiwnae 
III  well  ilMwii.   There  ie 


rarrants  the  f ol- 


Thb  Cabdiac  Sounds. 

Two  sounds,  differing  in  pitch,  duration,  and  intensity,  may 
be  heard  over  the  heart,  ^Len  the  chest  is  opened  and  the 
heart  listened  to  by  means  oi'  a  stethoscope.  These  sounds  may 
also  be  heard,  and  present  the  same  characters  when  the  heart 
is  auscultated  through  the  chest  wall ;  hence  the  cardiac  im- 
pulse can  take  no  essential  part  in  their  production. 

The  sounds  are  thought  to  be  fairly  well  represenic  ^,  so  far 
as  the  human  heart  is  concerned,  by  the  syllables  lub,  dv/p; 
the  first  soimd  being  longer,  louder,  lower-pitched,  and  "  boom- 
ing" in  quality;  the  second  short,  sharp,  and  high-pitched. 

In  the  exposed  heart,  the  first  sound  is  heard  most  distinct- 
ly over  the  base  of  the  organ  or  a  little  below  it;  while  the  sec- 
ond is  communicated  most  distinctly  over  the  roots  of  the  great 
vessels — that  is  to  say,  both  spunds  are  heard  best  over  the 
auriculo- ventricular  and  semiliuiar  valves  respectively.  When 
the  oh«3t  wall  intarvenes  between  the  heart  and  the  ear,  it  is 
foimd  that  the  second  sound  is  usually  heard  most  distinctly 
over  the  second  costal  cartilage  on  the  right ;  and  the  first  in 
the  fifth  costal  interspace  where  the  heart's  impulse  is  also 
often  most  distinct.  In  these  situations  the  arch  of  the  aorta 
in  the  one  case,  and  the  ventricular  walls  in  the  other,  are  close 
to  the  situations  referred  to  during  the  cardiac  systole;  hence 
it  is  inferred  that,  though  the  sounds  do  not  originate  directly 
beneath  these  spots,  they  are  best  propagated  to  the  chest  widl 
at  these  points. 

There  are,  however,  individual  differences,  owing  to  a  va- 


iii»rtniiiiiiiiii«,-a.,-,.»--i'»i 


286 


ANIMAL  PHTSIOLOOT. 


riety  of  causes,  which  it  is  not  always  possible  to  explain  fully 
in  each  case,  but  owing  doubtless  in  great  part  to  variations  in 
the  anatomical  relations. 

The  Oaiism  of  the  Bowids  of  fhe  Heart— There  is  general  agree- 
ment in  the  view  that  the  second  sound  is  owing  to  the  closure 
of  the  semilunar  valyes  of  the  aortic  and  pulmonary  vessels ; 
the  former,  owing  to  their  greater  tension  inconsequence  of  the 
higher  blood-pressure  in  the  aorta,  taking  much  the  larger  share 
in  the  production  of  the  sound,  as  may  be  ascertained  by  listen- 
ing over  these  vessels  in  the  exposed  heart.  When  these  valves 
are  hooked  back,  the  second  sound  disappears,  so  that  there  can 
be  no  doubt  that  they  bear  some  important  relation  to  the  cau- 
sation of  the  sound. 

In  regard  to  the  first  sound  of  the  heart  the  greatest  diver- 
sity of  opinion  has  prevailed  and  still  continues  to  exist.  The 
following  among  other  views  have  been  advocated  by  physi- 
ologists : 

1.  The  first  sound  is  caused  by  the  tension  and  vibration  of 
the  auriculo-ventricular  valves. 

2.  The  first  sound  is  owing  to  the  contractions  of  the  large 
mass  of  muscle  composing  the  ventricles. 

3.  The  sound  is  directly  traceable  to  eddies  in  the  blood. 

In  favor  of  the  first  view  it  was  argued  that  by  agreement 
the  second  sound  was  valvular,  and  why  not  the  first  ?— And 
again  that  malformations  of  the  valves  gave  rise  to  "  murmurs  " 
("  bruits"),  whicu  either  obscured  or  replaced  the  true  sound. 

The  second  opinion  was  supported  by  the  fact  that  the  larger 
the  heart  the  more  powerful  the  sound ;  that  when  the  blood 
was  cut  off  from  the  heart  by  ligature  of  the  vessels  success- 
ively, the  sound  coidd  still  be  heard ;  that  with  fatty  degenera- 
tion of  the  muscle-fibers  of  the  heart,  it  had  been  found  that 
the  sound  was  weak — and  similar  arguments. 

Recently  it  has  been  contended  very  strongly  that  the  first 
sound  may  be  heard  by  a  double  stethoscope  placed  6ver  an  ex- 
cised, bloodless,  mammalian  heart,  or  even  ventricle,  while  it 
still  beats. 

The  third  opinion  was  less  vigorously  upheld,  but  certain 
experiments  and  physical  phenomena  were  pointed  to  in  sup- 
port of  it. 

Against  the  arguments  adduced  above  it  may  be  stated  that 
the  first  sound  may  be  conceived  as  overpowered  by  a  hruU 
without  being  replaced  by  it  in  the  proper  sense  of  the  word. 
It  is  well  known  that  the  cardiac  muscle  is  peculiar,  occupying 


«^W)n  ?^'WWBiwtanaewqwwJ^'-fti'JWf-.»gfli 


tm^M-m 


THE  CIRCULATION  OP  THE  BLOOD. 


987 


►  explain  fully 
}  variations  in 

general  agree- 
:  to  the  closure 
Lonary  vessels ; 
sequence  of  the 
he  larger  share 
iined  by  listen- 
en  these  valves 

>  that  there  can 
bion  to  the  cau- 

greatest  diver- 
I  to  exist.  The 
ated  by  physi- 

nd  vibration  of 

}ns  of  the  large 

n  the  blood, 
t  by  agreement 
the  first  ?— And 
3  to  "murmurs" 
lie  true  sound, 
t  that  the  larger 
when  the  blood 
vessels  success- 
fatty  degenera- 
oeen  found  that 

jly  that  the  first 
aced  6ver  an  ex- 
mtricle,  while  it 

lield,but  certain 
>inted  to  in  sup- 
ay  be  stated  that 
<rered  by  a  bruit 
ense  of  the  word, 
juliar,  occupying 


in  structure  a  position  intermediate  between  the  stnped  vol- 
untary fibers  and  the  smooth  muscle-cells.  Numerous  mvesti- 
gationshave  shown  that  the  heart  is  not  susceptible  of  true 


Fm.Sll. 


na.fll«. 
F,«   «l.-lCJ««»0Plc  •Pp»««»-  «5L "K^Sr  tb.  ta«t     The  cro«trto,  dhrtalow. 

""oSi ;  ■c^towchliig  oelta. 

tetanic  contraction,  certainly  not  the  heart  of  the  mammal ;  so 
that  it  is  customary  to  term  the  cardiac  contraction  Pe^teltic. 
If  this  view  be  correct,  how  could  there  be  a  sound  P«>du^  by 
muscular  contraction  alone  P    To  this  it  haj  been  wphed  that 
the  sudden  tension  of  the  ventricuh^r  wall  when  tightened  over 
the  blood  may  give  rise  to  vibrations  that  account  for  the 
sound;  and recentinvestigationshave shown thatthevibi^ions 
that  rive  rise  to  the  sound  emitted  by  a  contracting  skelet^ 
muscle  may  be  fewer  than  was  once  supposed.    The  statement 
that  a  sound  may  be  heard  from  the  excised  ^'e'^*""}^^^^®' *^^ 
circumstances  above  mentioned  has  not  beeu  demed;  but  ite 
sourcehas  been  traced  to  the  action  of  *^«  j\f 'V!*^^*^*^' 
stethoscope!,  e.,  some  beUeve  the  sound  to  ^'JT*^"  ^ 
of  extrinsic  origin.    Most  physicians  would  be  very  l^th  to 
abandon  the  view  that  the  valves  are  always  to  be  taken  into 
seripus  account  as  a  factor  in  the  eausation  of  the  ^""JT' 
.--Sut.  looking  at  the  whole  question  broadly,  is  it  not  unrea. 
(sonable  to  explain  the  sound  resulting  from  such  a  complexact 
Mthe  contraction  of  the  heart  and  what  it  implies  m  the  light 
W  any  single  factor  ?    That  such  narrow  and  exclusive  vie^ 
should  have  been  propagated,  even  by  eminent  physiologiste. 
should  admonish  the  student  to  receive  with  great  caution  ex- 


288 


ANIMAL  PHT8I0L0OT. 


planationa  of  the  working  of  complex  organs,  based  on  a  single 
experiment,  observation,  or  argument  of  any  kind. 

The  view  we  recommend  the  student  to  adopt  in  the  light  of 
our  present  knowledge  is,  that  the  first  sound  is  the  result  of 
several  causative  factors,  prominent  among  which  are  the  sud- 
den tension  of  the  auriculo- ventricular  valves,  and  the  contrac- 
tion of  the  cardiac  muscle,  not  leaving  out  of  the  account  the 
possible  and  probable  influence  of  the  blood  itself  through 
eddies  or  otherwise;  nor  would  we  ridicule  the  idea  that  in 
some  cases,  at  all  events,  the  sound  may  be  modified  in  qiiality 
and  intensity  by  the  shock  given  to  the  chest  wall  during  sys- 
tole. 

Bndo-Cardiac  Prkssubks. 

Bearing  in  mind  the  relative  extmt  of  the  pulmonary  and 
systemic  portions  of  the  circulation,  we  should  suppose  that 
the  resistance  to  be  overcome  in  opening  the  aortic  valves  and 
lifting  the  column  of  blood  that  keeps  them  pressed  together, 
would  be  much  g^reater  in  the  left  ventricle  than  in  the  right ; 
or,  in  other  words,  that  the  intra-ventricular  pressure  of  the 
left  side  of  the  heart  would  greatly  exceed  that  of  the  right, 
and  this  is  confirmed  by  actual  experiment. 

By  means  of  an  instrument  known  as  the  maximum  and 
minimum  manometer,  the  highest  and  lowest  pressure  within 
any  chamber  of  the  heart  may  be  learned  approximately.  As 
a  specimen  measurement  it  may  be  stated  that  it  has  been 
found  that  in  a  dog  the  greatest  pressure  was  140  mm.  of  mer- 
cury for  the  left  ventricle,  for  the  right  only  60,  and  for  the 
right  auricle  20.  But  it  is  also  found— a  matter  not  quite  so 
obvious — ^that  Sk  minimum  pressure  proportionate  to  the  maxi- 
mum may  exist  in  all  the  chambers  of  the  heart;  and  the  press- 
ure may  fall  below  that  of  the  atmosphere,  or  be  negative.  By 
the  same  method  it  was  found  that  in  a  dog  the  negative  pressure 
varied  between  —62  and  —20  mm.  of  mercury  for  the  left  ven- 
tricle and  — 17  to  — 16  mm.  for  the  right,  with  — 12  to  —7  mm.  for 
the  right  auricle.  As  will  be  shown  later,  part  of  this  diminished 
preiteure  is  due  to  the  effect  of  the  respix-atory  movements ;  and, 
indeed,  more  recent  experiments  seem  to  show  that  ordinarily, 
with  the  heart  beating  with  its  usual  rate  and  force,  the  nega- 
tive pressure  or  suck  from  its  own  action  is  comparatively 
slight.  The  discussion  of  the  cause  of  this  negative  pressure, 
like  the  related  subject  of  the  cause  of  the  heart's  diastole,  has 
given  rise  to  much  difference  of  opinion. 


I'l '  iDi  wmmMJWiJriw 


jaowwiwiMiULBiiimftiiKir  m 


THE  CIBCULATION  OF  THE  BLOOD. 


289 


111 


led  on  a  single 
d. 

in  the  light  of 
8  the  result  of 
are  the  snd- 
d  the  contrac- 
he  account  the 
itself  through 
e  idea  that  in 
ified  in  quality 
all  during  sys- 


mlmonary  and 
d  suppose  that 
>rtic  valves  and 
ressed  together, 
ui  in  the  right ; 
pressure  of  the 
at  of  the  right, 

)  maximum  and 
pressure  within 
roximately.  As 
bat  it  has  been 
140  mm.  of  mer- 
60,  and  for  the 
ter  not  quite  so 
ate  to  the  maxi- 
t;  and  the  press- 
be  negative.  By 
negative  pressure 
for  the  left  ven- 
12  to —7  mm.  for 
f  this  diminished 
aovements;  and, 
'  that  ordinarily, 
1  force,  the  neg^ 
is  comparatively 
)gative  pressure, 
irt's  diastole,  has 


Some  find  it  difficult  to  understand  how  the  heart  after  sys- 
tole may  regain  its  original  form  apart  from  the  assistance  of 
diastolic  muscles,  which  are  assumed  to  act  so  as  to  antagonize 
those  causing  systole. 

Others  think  the  elasticity  of  the  heart's  muscle  sufficient  of 
itself  to  account  for  the  organ's  return  to  its  original  form. 

But  there  is  surely  a  misconception  involved  in  both  of 
these  views. 

If  small  portions  of  the  heart  of  the  frog,  tortoise,  or  other 
cold-blooded  animal,  just  removed  from  the  body,  be  observed 
under  a  microscope  it  will  be  seen  that  they  alternately  con- 
tract and  relax.  Now,  it  is  only  necessary  to  suppose  that  the 
relaxation  of  the  heart  is  complete  after  each  systole,  to  under- 
stand how  even  an  empty  heart  regains  its  diastolic  form. 

That  there  should  be  a  negative  pressure  in,  say,  the  left 
ventricle,  follows  naturally  enough  from  the  fact  that  not  only 
are  the  contents  of  the  ventricle  expelled  with  great  sudden- 
ness, but  that  its  walls  remain  (see  Figa  210  and  214)  pressed 
together  for  a  considerable  portion  of  the  time  occupied  by  the 
whole  systole;  so  that  in  relaxation  it  follows  that  there  must 


no.  SlS.-1>ia«ram  riMmlK  *>»  NiatlTO  Mglit  o(  tto  blood-imMira  In  dMOraat  pM^ 

TMoolar  nralani  toflarrm).   A,  taMrt ;  a,  artattotai :  «,  mall  vrins ;  il,  wtartea ;  e,  cm>- 

Mood gilwwiiTilirifafdby the ht^teot Ui*«  "^     .-~~-i— .  «^ 

pwwe,  apiirazimatoljr,  in  mm.  of  merourjr. 


vo«  1.  v.)  sftmosphorfc 
ThenmdMnoB  the*  Ml  gtni  the 


be  an  empty  cavity  to  fill,  or  that  there  must  be  an  aspiratory 
effect  toward  the  ventricle ;  hence  also  one  factor  in  the  closure 
of  the  semilunar  valves. 


mJWil.WWUMlUJi.l'Ui.-Mlu* 


240 


ANIMAL  PHrSIOLOOY. 


It  thus  appears  that  the  heart  is  not  only  a  force>pump  but 
also  to  some  extent  a  e.  c't'  ;^  >nmp;  and,  if  so,  the  aspirating 
effect  must  express  itself  >  ■  vhe  threat  veius,  lacking  valves  as 
they  do,  at  their  entrance  i  'A^-i  heart ;  hence,  with  each  dias- 
tole the  blood  would  be  sucked  on  into  the  auricles,  a  result 
that  is  intensified  by  the  respiratory  movements  of  the 
thorax. 

BelatiT*  Time  ooovpisd  byth*  ▼•rioni  FhMM«f  th*  Cardiae  0yd*. 
— The  old  and  valuable  diagram  reproduced  below  is  meant  to 
convey  through  the  eye  the  relations  of  the  main  events  in  a 
complete  beat  of  the  heart  or  cardiac  cycle.     The  relative 

length  of  the  sounds;  the 
long  period  occupied  by  the 
pause ;  the  duration  of  the 
ventricular  systole,  which 
it  is  to  be  observed  is  in 
excess  of  that  of  the  first 
sound,  are  among  the  chief 
facts  to  be  noted. 

The  tracings  of  Chau- 
veau  and  Marey,  obtained 
from  the  heart  of  the  horse> 
which  has  a  very  slow 
rhythm,  show  that  of  the 
whole  period,  the  auricular 
systole  occupies  |  or  ^  of 
a  second ;  the  ventricular 
systole,  f  or  ^  of  a  sec- 
ond ;  and  the  diastole,  f  or  ^  of  a  second. 

With  the  more  rapid  beat  in  man  (70  to  80  per  minute),  the 
duraticm  of  the  cardiac  cycle  may  be  estimated  at  about  ^  of 
a  second,  and  the  probable  proportions  for  each  event  are  about 
these:  The  auricular  systole,  ^  of  a  second;  the  ventricular 
systole,  ^  of  a  second ;  and  the  pause,  ^  of  a  second. 
^  It  will  be  noted  that  the  pause  of  the  heart  is  M^ual  in  dura- 
/  tion  to  the  other  events  put  together;  and  even  assuming  that 
there  is  some  expenditure  of  energy  in  the  return  (relaxation) 
of  the  heart  to  its  passive  form,  there  still  remains  a  consider- 
able interval  for  rest,  so  that  this  organ,  the  very  type  of  cease- 
less activity,  has  its  periods  of  complete  repose. 


Fio.  814.  — Dia^raiii  nptmeaOat  the  moweauita 
•ndMMadaoC  IIm  aautdumgrncariimocrck 

(aflarSharpejr). 


THE  CIRCULATION  OP  THE  BLOOD. 


241 


'orce-pump  but 
the  aspirating 
king  valves  as 
with  each  dias- 
iricles,  a  result 
ements  of    the 

OazdlMCTol*. 

ow  is  meant  to 

lain  events  in  a 

The  relative 

ihe  sounds;  the 

occupied  by  the 

duration  of  the 

systole,  which 

observed  is  in 

)hat  of  the  first 

among  the  chief 

noted. 

usings  of  Chau- 
Marey,  obtained 
eart  of  the  horse> 
us    a   very   slow 
how  that  of  the 
iod,the  auricular 
supies  I  or  A  of 
the  ventricular 
or  ^  of  a  Bee- 
per minute),  the 
id  at  about  -^  of 
li  event  are  about 
;  the  ventricular 
i  second. 

is  equal  in  dura- 
>n  assuming  that 
turn  (relaxation) 
mains  a  consider- 
ery  type  of  cease- 


The  Work  of  the  Heart. 

Since  the  pressure  against  which  the  heart  works  must,  as 
we  shall  see,  vary  from  moment  to  moment,  and  sometimes  very 
considerably,  the  work  of  the  heart  must  also  vary  within  wide 
limits,  even  making  allowance  for  large  adaptability  to  the  bur- 
den to  be  lifted ;  for  it  will  be  borne  in  mind  that  the  degree 
to  which  the  heart  empties  its  chambers  is  also  variable. 

'  If  one  knew  the  quantity  of  blood  ejected  by  the  left  ven- 
tricle, and  the  rate  of  the  beat,  the  calculation  of  the  work 
done  would  be  an  easy  matter,  since  the  former  multiplied  by 
the  latter  would  represent,  as  in  the  case  of  a  skeletal  muscle, 
the  work  of  the  muscles  of  the  left  ventricle ;  from  which  the 
work  of  the  other  chambers  might  be  approximately  calculated. 

The  work  of  the  auricles  must  be  slight,  considering  that  the 
filling  of  the  ventricles  is  not  dependent  solely  upon  their  con- 
traction, that  they  empty  themselves  very  imperfectly,  and 
that  the  tracing  on  Marey's  curves  (Fig.  210),  representing  the 
effect  of  their  contraction  on  the  intraventricular  pressure  is 
but  smalL  Notwithstanding,  as  they  largely  determine  by 
their  contraction  and  the  quantity  they  throw  into  the  ventri- 
cles how  full  the  latter  shall  be  in  a  given  instance,  they  really 
have  a  very  large  share  in  determining  the  total  work  of  the 
ventricles  and  the  whole  heart. 

/^>  The  right  ventricle,  it  is  estimated  does  from  one  fourth  to 
^one  third  the  work  of  th<i  left ;  not,  of  course,  because  it  throws 
out  less  blood,  for  if  this  were  the  case  the  left  side  of  the  heart 
must  soon  become  empty,  not  to  mention  other  disturbances  of 
the  vascular  equilibrium,  but  because  of  the  relatively  less 
resistance  offered  by  the  pulmonary  vessels. 
/nAU  attempts  to  estimate  exactly  the  quantity  ejected  by  the 
left  ventricle  seem  to  show  that  this  varies  very  greatly,  after 
due  allowance  is  made  for  the  imperfection  of  the  methods  and 
the  great  discrepancies  in  the  results  of  different  observers. 
Perhaps  six  ounces,  or  about  180  grammes,'may  be  taken  as  an 
average  for  the  left  ventricle  of  man.  Assuming  that  his  aortic 
blood-pressure  is,  say  200  mm.  of  mercury  or  3*21  metres  of 
blood,  the  work  of  this  chamber  for  each  beat  would  be  180  X 
3*21 ,  or  578  gramme-metres.  If  the  heart  beats  seventy  times  per 
minute,  the  work  for  the  day  would  be  678  X  70  X  60  X  24  =  68,- 
262,400  gramme-metres.  Or,  upon  the  same  basis,  and  assuming 
that  the  blood  makes  up  about  the  one  thirteenth  of  the  weight 
of  the  individual,  in  a  man  of  143  pounds,  the  whole  of  the 
1« 


»fi'?'r'lRRp«ft2Jl55i^)ii,^i7iE*r^*?^^ 


iffr-'i^yj'-'ic^?y?!s^-:ff;:^A^vn"g?v'rv^*-;'^i^j*'.g'^'vMr' 


■■UII.AWW  'VMWWI.W.It'" 


242 


ANIMAL  PHTSIOLOOY. 


blood  would  pass  through  the  heart  in  about  thirty  beats,  or 
in  l§ss  than  half  a  minute. 

CjVhen  we  calculate  the  work  done  by  the  heart  for  certain 
intervals,  as  the  day,  the  week,  month,  year,  and  especially  for 
a  moderate  lifetime,  and  compare  this  with  that  of  any  ma- 
chine it  is  within  the  highest  modem  skill  to  construct,  the 
great  superioidty  of  the  vital  pump  in  endurance  and  working 
capacity  will  be  very  apparent ;  not  to  take  into  the  account  at 
all  its  wonderful  adaptations  to  the  countless  vicissitudes  of  life, 
without  which  it  would  be  absolutely  useless,  even  destructive 
w  the  organism. 

Some  of  these  variations  in  the  working  of  the  heart  we  may 
now  to  advantage  consider. 


Variations  in  the  Cardiac  Pulsation. 

These  may  be  ascertained  either  by  the  investigation  of  the 
arteries  or  of  the  heart,  for  every  considerable  alteration  in  the 
working  of  the  heart  expresses  itself  also  through  the  arterial 
system.  In  speaking  of  the  pulse,  the  reference  is  principally 
to  the  arteries,  but  in  each  case  we  may  equally  well  think  of 
the  heart  primarily  as  acting  upon  the  arteries. 

1.  The  frequency  of  the  heart-beat  varies,  as  might  be  sup- 
posed, with  a  great  multitude  of  conditions,  the  principal  of 
which  are :  age,  being  most  f  isequent  at  birth,  when  it  may  be 
140  per  minute,  gradually  8lov.nng  to  old  age,  when  it  may  fall 
to  60.  In  feeble  old  age  the  heart-beat  may,  like  many  other  of 
the  functions  of  the  body,  approximate  the  infantile  condition, 
being  very  frequent,  small,  feeble,  and  easily  disturbed  in  its 
rhythm. 

It  is  a  matter  of  no  small  importance  to  the  medical  student 
to  be  aware  of  the  normal  rate  for  different  periods  of  life, 
hence  we  give  below  a  pretty  full  statement  of  the  variations 
with  age.  It  will  be  understood  that  the  numbers  are  only  ap- 
proximative, and  that  large  allowance  must  be  made  for  indi- 
vidual deviations :  .    . 

At  4  years,  96-94 

6  '  "      94-90 

10      "      90-86 

16      "      80-76 

Sex.— The  cardiac  beat  is  more  frequent  in  females ;  aMwre, 
more  frequent  in  the  short ;  posture,  most  rapid  in  the  standing 
position,  slower  when  sitting,  and  slowest  in  the  recumbent 


At  birth,  130-140 
lyear,  120-180 
2  years,  100-110 
8      "     100-  96 


At  20  years,  78-72 
80  "  76-70 
60     "      70-66 


THE  CIRCULATION  OP  THE  BLOOD. 


243 


thirty  beats,  or 

sart  for  certain 
i  especially  for 
lat  of  any  ma- 
j  construct,  the 
se  and  working 
a  the  account  at 
lissitudes  of  life, 
)ven  destructive 

be  heart  we  may 


A.TION. 

istigation  of  the 
alteration  in  the 
agh  the  arterial 
36  is  principally 
ly  well  think  of 

• 

s  might  be  sup- 
the  principal  of 
when  it  may  be 
when  it  may  fall 
ke  many  other  of 
Eantile  condition, 
disturbed  in  its 

)  medical  student 
t  periods  of  life, 
9f  the  variations 
ibers  are  only  ap- 
e  made  for  indi- 

iO  years,  78-72 
80  "  75-70 
50     "       70-66 

females;  ataiure, 
id  in  the  standing 
in  the  recumbent 


posture ;  season,  more  frequent  in  summer ;  period  of  the  day, 
more  frequent  in  the  afternoon  and  evening ;  elevation  of  iem- 
perature,the  inspiratory  act;  emotions  and  mental  activity,  eating, 
muscular  exercise,  etc.,  render  the  heart-beats  more  frequent. 

2.  The  length  of  the  systole,  though  variable,  is  more  con- 
stant than  that  of  the  diastole.  The  estimated  limits  of  the 
systole  may  be  stated  as  '327  to  *301  second. 

3.  The  force  of  the  puiaation  varied  very  greatly  and  exer- 
cises an  important  influence  on  the  blood-pressure,  and  the 
velocity  of  the  blood-stream.  As  a  rule,  when  the  heart  beats 
rapidly,  especially  for  any  considerable  length  of  time,  the  force 
of  the  individual  pulsations  is  diminished. 

4  The  heart-beat  may  vary  much  and  in  ways  it  is  quite 
possible  to  estimate,  both  directly  by  the  hand  placed  over  the 
organ  on  the  chest,  by  the  modifications  of  the  cardiac  sounds, 
and  by  the  use  of  Instruments.  It  is  wonderful  how  much  in- 
formation may  be  conveyed,  without  the  employment  of  any 
instruments,  through  palpation  and  auscultation,  to  one  who 
has  long  investigated  the  heart  and  the  arteries  with  an  intelli- 
gent, inquiring  mind ;  and  we  strongly  recommend  the  student 
to  commence  personal  observations  early  and  to  maintain  them 
persistently. 

y\  Physicians  recognize  the  pulse  (and  heart)  as  "  slow  "  as  dis- 
4ing^iished  from  "  infrequent,"  "  slapping,"  "  heaving,"  "  thrill- 
ing," "1  founding,"  etc. 

Now,  if  with  these  terms  there  arise  in  the  mind  correspond- 
ing mental  pictures  of  the  action  of  the  heart  under  the  cir- 
cumstances, well ;  if  not,  there  is  a  very  undesirable  blank. 
How  the  student  may  be  helped  to  a  knowledge  of  the  actual 
behavior  of  the  heart  under  a  variety  of  conditions  we  shall 
endeavor  to  explain  later. 

Apart  from  all  the  above  peculiarities,  the  heart  may  cease 
its  action  at  regular  intervals,  or  at  intervals  which  seem  to 
possess  no  definite  relations  to  each  other — that  is,  the  heart 
may  be  irregular  in  its  action,  which  may  be  made  evident 
either  to  the  hand  or  the  ear. 

There  are  certain  deviations  from  the  quicker  rhythm  which 
occur  with  such  n;gularity  and  are  so  dependent  on  events  that 
takes  place  in  other  parts  of  the  body  that  they  may  be  con- 
sidered normal.  Reference  will  shortly  be  made  to  these  and 
the  causes  of  the  variations  enumerated  in  this  sectio  .. 

Oompantivt.— The  following  table  gives  the  mean  number  of 
cardiac  pulsations  per  minute  (after  Oamgee*) : 


244 


ANIMAL  PHYSIOLOaT. 


SPKCIBS. 

Adnlt. 

Tonth. 

Old  age. 

Horse 

8fr-40 
46-50 
45-50 
70-  80 

m-m 

90-100 
190-140 

60-72 

65-  75 

60-  70 

85-  95 

100-110 

110-120 

180-140 

82-  88 

Aw  and  mule 

Ox.     

55-  60 
40-  45 

Sheen  and  sroat 

65-  60 

piT^/!^^.::::::: :::::::::::::: 

65-  60 

Doir 

60-  70 

Cat 

100-120 

The  variations  with  age,  for  the  horse  and  the  ox,  are  as  fol- 
lows, according  to  Kreutzer :  ' 


Horw, 

At  birth. 100-120 

When  14  days  old 80-96 

When  8  months  old 68-76 

When  6  months  old 04-72 

Whenlyearold 4&- 56 

When  2  years  old 40-48 

When  8  years  old 88-48 

When  4  years  old 88-60 

When  aged 82-40 


Ox. 

Atbirth...     92-182 

When  4-5  days  old 100-120 

When  14  days  old 68 

When  4-6  weeks  old 64 

When  6-12  months  old 56-68 

For  the  young  cow 46 

For  the  four-yeai>old  ox 40 


Thb  Pulse. 

Natiu'ally  the  intermittent  action  of  the  heart  gives  rise  to 
corresponding  phenomena  in  the  elastic  tubes  into  which  it 
may  be  said  to  be  continued,  for  it  is  very  desirable  to  keep  in 
mind  the  complete  continuity  of  the  vascular  system. 

The  following  phenomena  are  easy  of  observation :  When  a 
finger-tip  is  laid  on  any  artery,  an  interrupted  pressure  is  felt ; 
if  the  vessel  be  laid  bare  (or  observed  in  an  old  man),  it  may 
be  seen  to  be  moved  in  its  bed  forward  and  upward ;  the  press- 
ure i8  loss  the  farther  the  artery  from  the  heart ;  if  the  vessel 
be  opened,  blood  flows  from  it  continuously,  but  in  spurts ;  if 
one  finger  be  laid  on  the  carotid  and  another  on  a  distant  ves- 
sel, as  one  of  th^  arteries  of  the  foot,  it  may  be  observed  (though 
it  is  not  easy,  from  difficulty  in  attending  to  two  events  hap- 
pening so  very  close  together)  that  the  beat  in  the  nearer  ves- 
sel precedes  by  a  slight  interval  that  in  the  more  distant. 

Investigating  the  latter  phenomenon  with  instruments,  it  is 
found  that  an  appreciable  interval,  depending  on  the  distance 
apart  of  the  points  observed,  intervenes. 

Whau  is  the  explanation  of  these  facts  ? 

The  student  may  get  at  this  by  a  few  additional  observa- 
tions that  can  bo  Easily  made. 


1. 

r2 

Old  age. 

82-88 

rs 

56-60 

70 

40-  46 

ffi 

66-60 

10 

66-60 

20 

60-70 

40 

100-120 

9  OX,  are  as  fol> 

r. 

02-182 

100-120 

68 

1 64 

old 66-68 

46 

d  ox 40 


art  gives  rise  to 
IS  into  which  it 
rable  to  keep  in 
jrstem. 

vation :  When  a 
pressure  is  felt ; 
Id  man),  it  may 
nrard ;  the  press- 
rt ;  if  the  vessel 
mt  in  spurts;  if 
on  a  distant  ves* 
observed  (though 
two  events  hap- 
1  the  nearer  ves- 
re  distant, 
nstruments,  it  is 
on  the  distance 


litional  observa- 


THE  CIRCULATION  OP  THE  BLOOD. 


245 


If  water  be  sent  through  a  long  elaittic  tube  (so  coiled  that 
points  near  and  remote  may  be  felt  at  the  same  time)  by  a  bulb 
syringe,  imitating  the  heart,  and  against  a  resistance  made  by 
drawing  out  a  glass  tube  to  a  fine  XK>int  and  inserting  it  into 
tne  terminal  end  of  the  rubber  tube,  an  intermittent  pressure 
like  that  occurring  in  the  artery  may  be  observed ;  and  further 


Fio.  916.— Mwey'a  meotntxm  for  showtnK  Um  mode  in  whidi  ths  duIm  la  propagated  in  tlie 
arteriea.  B,  a  niSber  pump,  with  TaiTea  to  pravent  regurgitation.  The  wonting  of  tlie 
apparatus  will  be  apparent  mm  Um  inepeotion  of  the  iigure. 

that  it  does  not  occur  at  precisely  the  same  moment  at  the  two 
points  tested. 

Information  more  exact,  though  possibly  open  to  error,  may 
be  obtained  by  the  use  of  more  elaborate  apparatus,  and  the 
graphic  method. 

Fig.  216  gives  an  idea  of  the  main  features  of  th9  pulse-trac- 
ings of  an  arterial  scheme  or  arrangement  of  tubes  in  supposed 
imitation  of  the  conditions  existing  in  ^e  vascular  system  of 
the  mammalian  body.  Attention  is  especially  directed  to  the 
abrupt  ascent,  the  more  gradual  descent,  uid  the  secondary 
waves,  which  are  either  waves  of  oscillation  or  reflex  waves. 

It  may  also  be  noticed  that  the  rise  is  later  as  the  part  of 
the  tube  at  which  it  occurs  is  more  distant  from  the  pump ; 
also  that  it  gets  gradually  less  in  height  and  at  the  same  time 
that  all  the  secondary  waves  are  diminished  or  iotally  disap- 
pear ;  and  with  the  exception  of  the  latter  these  results  hold 
good  of  the  pulse  in  the  arteries  of  a  living  animal. 

By  measurement  it  has  been  ascertained  that  in  man  the 
pulse- wave  travels  at  the  rate  of  from  five  to  ten  metres  per  sec- 
ond, being  of  course  very  variable  in  velocity.  It  would  seem 
that  the  more  rigid  the  arteries  the  more  rapid  the  rate,  for  in 


Mi*tm 


WW  wwmi  ifMtiiniHiiwMiminHww*^ 


246 


ANIMAL  PHYSIOLOGY. 


children  with  their  more  elastic  arteries  the  speed  is  slower; 
and  the  same  principle  is  supposed  to  explain  the  higher  veloci- 


wvXaKaAaaaKaa/vvvvv 


alaat  an  elMtlc  tube  Into  which  fluid  la  foroed  By  the  sudden  rtroke  of  a  pump.  The 
imU  indicate  the  onwaiil  and  the  reflected  wafja  the  gradual  flattenUiK  and  \otal  or 
partial  extinction  of  the  wuvee  are  noteworthy  (after  Harey). 

ty  noticed  in  the  arteries  of  the  lower  extremities.  But  with 
such  a  speed  as  even  five  metres  a  second  it  is  evident  that  witU 
a  systole  of  moderate  duration  (say  "3  second)  the  most  distant 
arteriole  will  have  been  reached  by  the  pulse-wave  before  that 
«ysfcole  is  completed. 

It  is  known  that  the  blood-current  at  its  swiftest  has  no 
Huch  speed  as  this,  never  perhai  s  exceeding  in  man  half  a  metre 
per  second,  so  that  the  pulse  and  t^^e '  lood-current  must  be  two 
total)  J  distinct  things. 


iwiniiwar' I 'I'litunii 


mmm 


THE  CIRCULATION  OP  THE  BLOOD. 


247 


The  student  may  very  simply  iUustrate  this  matter  for  him- 
self. By  tapping  sharply  against  a  pipe  through  which  a 
stream  is  flowing  slowly  and  quietly,  a  wave  may  be  seen  to 
arise  and  pass  with  considerable  velocity  along  the  moving 
water,  and  with  a  speed  far  in  excess  of  the  rapidity  of  the  main 
current.  When  the  left  ventricle  throws  its  six  ounces  of  blood 
into  vessels  already  full  to  distention,  there  must  be  consider- 
able concussion  in  consequence  of  the  rapid  and  forcible  nature 
of  the  cardiac  systole,  and  this  gi\  es  rise  to  a  wave  in  the  blood 
which,  as  it  passes  along  its  isurface,  causes  each  part  of  every 
artery  in  succession  to  respond  by  an  elevation  above  the  gen- 
eral level,  and  it  is  this  which  the  finger  feels  when  laid  upon 
an  artery. 

That  there  is  considerable  distention  of  the  arterial  system 
with  each  pulse  may  be  realized  in  various  ways,  as  by  watch- 
ing and  feeling  an  artery  laid  bare  in  its  course,  or  in  very 
thin  or  very  old  people,  and  by  noticing  the  jerking  of  one  leg 
crossed  over  the  other,  by  which  method  in  fact  the  pulse-rate 
may  be  ascertained.    And  that  not  only  the  whole  body  but^ 
the  entire  room  in  which  a  person  sits  is  thrown  into  vibration  '. 
by  the  heart's  beat,  may  be  learned  by  the  use  of  a  telescope  to  \ 
observe  objects  in  the  room,  which  may  thus  be  seen  to  be  in) 
motion. 

FeatoTM  of  an  Artorial  PulM-Tnuifaf . — In  order  to  judge  of  the 
nature  of  arterial  tracings,  it  is  important  that  the  circum- 
stances under  which  they  are  obtained  shoiild  be  known. 

The  movements  of  the  vessel  wall  in  most  mammals  stiit- 


n  plwwd  a>  om.  uMi 
roke  of  »  pump.  The 
iteUening  Mid  total  or 


ties.  But  wit>j 
idiant  that  wiiii 
he  most  distant 
ave  before  that 

jwiftest  has  no 
an  half  a  metre  < 
mt  must  be  two 


Fio.  mr.—Mbrer'i  ImprovMt  n;>hyKiiK«Ta|ih  MTMyrad  for  UkloR  •  tnwlnc.  A,  Heel  spring ; 
B.  ttttt  lever ;  C,  wriUiw-terer ;  C\  Urn  free  wrftiag  end  ;  D,  acrew  forl>riiiRinK  B  in  con- 
tact with  C ;  a,  lUde  wlHi  Mnoked  paper :  B,  olook-work ;  L,  wsrew  for  increaaiBK  the 
preesure :  .W.  dial  Indlcattnff  the  amount  of  iMc«nire ;  K,  K,  atrape  forjteing  the  InMru- 

*   **- -  ^  -' '    -  *'  —■    '       or  M|iport  (By rum  Bnmwsll). 


mnnt  to  the  arm,  and  the  latter  to  the  dPUble-lncUiied 


iMIIWWWmK'WWgW 


248 


ANIMAL  PHTSIOLOOY. 


able  for  experiment  and  in  man  is  so  slight  that  it  becomes  ne- 
cessary to  exaggerate  them  in  the  tracing,  hence  long  levers  are 
used  to  accomplish  this. 

The  sphygmograph  is  the  usual  form  of  instrument  em- 
ployed for  the  purpose.  It  consists,  essentially,  of  a  clock-work 
for  moving  a  smoked  surface  (mica  plate  commonly)  on  which 

the  movements  of  a  lever-tip, 
answering  to  those  of  a  button 
placed  on  the  artery,  are  re- 
corded. 

Considering  the  nature  of  the 
pulse  and  the  apparatus  em- 
ithe  eMenaupMtot  the  inatnim^  ployed  to  Write  its  characters,  it 
B",ottbe1dtorfieverisinco^Mir«1Si   will    be  seen  that  the  possible 

the  writityt-lerer,  C.    'Smn  iiK>?«meiit    __„____  _*  ->«_-»_  ___  ».,,,„«_^„„ 

or  the  Htoei  qpriiig  at  A",  comninnicA.   sources  Of  error  are  numerous. 

IS^iaffi^-K^S'^^^Sl.'SfflSl?'"        Different  observers  have,  as 

a  matter  of  fact,  even  with  the 
same  sort  of  instrnaient  obtained  tracings  differing  not  a  little 
in  character.  Aa  tht>  subjoined  figures  show,  the  pressure  ex- 
erted upon  a  vessel  may  so  alter  the  result  that  entire  features 
of  the  tracing  may  actually  disappear.  The  sphygmograph, 
even  in  the  most  skillful  hands,  has  proved  somewhat  disap- 
pointing OS  a  physiological  and  especially  as  a  clinical  instru- 
ni  tnt,  though  it  is  not  without  a  certain  value. 

We  shall  do  well  to  inquire  whether  there  are  any  features 
in  common  in  tracings  obtained  in  various  ways,  and  which 
have  therefore  in  all  probability  a  real  foundation  in  nature. 

An  inspection  of  a 

ISST^'Sr,  AAAAMAAMAAAyU 

diverse  cdnditions, 
seems  to  show  that  in 
all  of  them  there  oc- 
curs, more  or  less 
marked,  the  follow- 
ing :  1.  \n  upward 
curve.  2.  A  downward 
curve,  rendered  irreg- 
ular by  the  occurrence 
of  peaks  or  crests  and 
notclies.  The  first  of  these  are  termed  the  predicrotic  notch  and 
crest.,  Hi^d  the  succeeding  ones  the  dicrotic  notch  and  crest. 
The  latter  woem  to  be  the  more  constant. 


Fw.  119.— Pnlae-tnMdiiK  from  carotid  artaiT  oT  healthy 
mM  (after  MoemiJ;  <r,  ooairoeiioemeat  oC  ezpaMlon 
<rfaiwi7;  4,nnDiiitt  of  flntrlw;  C,  diorotio  Keawl- 
aiy  WATD ;  «,  pcvdiorotio  Meondary  wave ;  p,  Mtoh 
pTBCiwMiigthle;  P.«ucc«edto|t— ooadpty  wa^e.  dnro 
above  to  Uiat  made  by  a  toBing-fork  with  ten  double 
vlbratkNia  In  a  leoond. 


mmm*  -"  i '  —h 


TH£  CIRCULATION  OF  THE  BLOOD. 


349 


it  becomes  ne- 
long  levers  are 

nstrument  em- 
of  a  clock-work 
only)  on  which 
of  a  lever-tip, 
>8e  of  a  button 
artery,  are  re- 
he  nature  of  the 
apparatus   em- 
ts  characters,  it 
at  the  possible 
ire  numerous, 
ervers  have,  as 
,  even  with  the 
»ring  not  a  little 
he  pressure  ex- 
t  entire  features 
sphygmograph, 
omewhat  disap- 
i  clinical  instru- 

ire  any  features 
vays,  and  which 
ion  in  nature. 


roUd  artary  of  hMlthy 
enoemeM  ot  expaMton 
riw;  C,  diorotio  waaMl- 
wdMy  «»▼• ;  p.  Match 
moobOpit  wave.  Carro 
lag-fork  with  ten  double 


icrotic  notch  and 
notch  and  crest. 


That  these  are  genuine,  answer  of  real  and  corresponding 
elevations  of  the  arterial  wall  and  of  the  blood-current  itself, 
seems  probable  from 
the  study  of  a  hcemau- 
togram.  The  latter  may 
be  obtained  by  allowing 
the  blood  from  a  cut 
artery  to  spurt  against 
a  piece  of  paper  drawn 
in  front  of  the  blood- 
stream. It  is  also  as- 
serted that  by  a  tele- 
phonic connection  with 
an  artery  both  the  pri- 
mary pulse-wave  and 
the  dicrotic  wave  may 
be  heard.  More  rarely 
there  are  interruptions 
in    the    first     upward 

curve,  termed  antwrotio  curves,  as  distinguished  from  those  in 
the  downward  curve  known  as  kcUaerotic. 

It  has  been  generally  admitted  that  the  first  marked  upward 

curve  is  due  to  the  systolic 
shock. 

The   following    are,  in 

an.-AoM)rotioiNii»tnM3incfn>mcaroUdof  brief,  some  of  the  views 
''^^^  that  have  been  entertained 

in  regard  to  the  minor  features  of  the  tracings : 

(a.)  That  the  predicrotic  wave-crest  is  owing  to  the  sudden 
arrest  of  the  flow  from  the  ventricle. 

(6.)  That  the  dicrotic  wave  is  a  wave  of  oscillation. 


Fig.  tn.'  -PulM-ciirve  from  radial  of  man.  Tkken  with 
aa  eztnHraaoular  praawire  of  70  nun.  of  taeroarj. 
The  cwTfed  Intermpted  Mnee  ibow  the  dtatanoefrom 
oneaMithertaitinieot  the  «hlef  phawa  ot  the  potae- 
wvn.  x,thecoiiimenoement,aiMl^,theclaaeaf  ex- 
paiMJkiii  of  atterr ;  p,  predicrotic  notidi :  d,  dicrotic 
notdi;  Cdicroao  orea*  '  " 

the  pok^dicrotlc  notdi. 


mcroHc  noion :  a,  aioroiic 
/>,  poat-dicrotle  creat ;  /, 


^fYWW 


Fm, 


Fto.  SSiS.— Two  grades  of  marked  dicrotiam  in  radial  pulae  of  man  (typhoid  f^verv 

(c.)  That  it  is  a  wave  of  reflection  from  the  periphery. 

(d.)  That  it  is  caused  by  the  sudden  closiire  of  the  aortic 
valves. 

It  appears  to  be  now  pretty  well  agreed  that  the  theory  of 
reflection  is  untenable  on  physical  principles;  that  a  high 
blood-f>re88ure  tends  to  render  the  kataomtic  markings  less 


i-«aa'i<MihilBlii>inwli.mMi< 


:~rrr'..'".\"m-mm!m 


wfmm 


950 


ANIMAL  PHYSIOLOGY. 


distinct,  and  the  reverse  when  the  pressure  is  low,  as  after 
hiemorrhages.     These  features  are  especially  marked  m  the 


no.  ns.— Normal  putae^sarre  in  the  aorU  from  the  dog. 

dicrotic  pulse  of  fever,  ete.,  when  the  blood-pressure  is  low  and 
may  be  recognized  even  by  the  hand.    The  anacrotic  crests 

and  notches  are  abnormal,  and  probably 
»  due  to  excessive  rigidity  of  the  arteries. 

Certain  it  is  that,  without  any  change 
in  the  heart-beat,  changes  in  the  tracings 
may  arise,  owing  to  modifications  in  the 
periphery  of  the  vascular  system.  We  do 
not  propose  to  discuss  the  above-men- 
ito.  «»*-^^'»«S[^"^£  tioned  views  of  the  causation  of  the  minor 
the^^^wcMTUina  features  of  the  tracings  in  detail,  about 
'**°'  which  the  greatest  diflferences  of  opinion 

still  prevail.  Even  if  all  the  characteristics  of  an  arterial 
tracing  could  be  ob- 
tained from  an  arti- 
ficial schema,  it 
would  not  follow 
that  the  conditions 
in  each  case  were 
the  same ;  in  fact, 
as  we  view  the  mat- 
ter, it  would  be  all 
but  impossible  that 
such  should  be  the 
case. 

Bubbev  tubes  are 
not  comparable  to 
arteries;  and  espe- 
cially not  to  arteri- 
oles and  capillaries. 
Bearing  in  mind  the 
peculiar  nature  of  the  blood-corpuscles;  their  relation  to  the 
walls  of  the  vessels  in  which  they  flow;  the  relation  of  the 


Fio.  aB.^bifliMBoe  of 
the  exterior  o(,the 


!«■  in  the  pNMure  Mipiied  to 
(eztr»-vMculMr)  on  the  form  of 


^SMTwUh  an  extHWUftwHa  Brewire  of,  ino,  TO  mm.. 
In  a',  to  80  mm.,  rati  in  a",  to 


mm.  merciuy. 


8MMI« 


THB  CIRCITLATION  OF  THB  BLOOD. 


251 


low,  as  after 
larked  in  the 


ire  is  low  and 
uacTotic  crests 
and  probably 
the  arteries, 
at  any  change 
m  the  tracings 
Lcations  in  the 
^stem.  We  do 
le  above-men* 
>n  of  the  minor 
1  detail,  about 
ices  of  opinion 
of  an  arterial 


le  prMMm  applied  to 
■acuter)  on  the  ronn  of 
»  mMi  of  twenM'-MTMi 
Hure  of,  in  o,  TV  mm., 
im.m««ui7. 


relation  to  the 
relation  of  the 


no.  ns.— IXorotlc  pulM-curre  due  to  luemoRliagie.  Ftam 
carotid  o(  rabbit,  with  extra-Taacular  prcwwire  of,  in  a, 
BO  mm.,  6,  of  40  mm.,  c,  of  W  mm.,  and  d,  of  10  mm. 
vaeKurr.  (Thia  and  the  precc«ling  lix  tracinfi  from 
Foater.I 


blood  to  the  nutrition  of  the  tissues;  the  fact  that  all  the  tubes 
that  compose  the  vascular  system  are  made  up  of  living  cells ; 

that   some    of    these  ,^ ^ 

cells  (in  arterioles  and 
capillaries)  are  in  a 
semi-fluid  condition — 
in  a  word,  that  the 
conditions  of  the  cir- 
culation as  a  whole 
are  aui  generis,  be- 
cause of  their  vitality 
— it  seems  to  us  amaz- 
ing that  purely  physical  explanations,  such  as  would  answer 
for  a  pump  and  set  of  rubber  tubes,  should  ever  have  been 
deemed  satisfactory.  The  whole  subject  seems  to  be  involved 
in  a  gross  misconception,  and  should  be  regarded,  we  must 
think,  from  an  entirely  new  standpoint. 

Temnis  Pnlas. — Apajrt  from  the  variations  in  the  caliber  of 
the  great  veins  near  the  heart,  constituting  a  sort  of  pulse, 
though  due  to  variations  in  intra-cardiac  pressure,  a  venous 
pulse  proper  is  rare  as  a  normal  feature.  One  of  the  best- 
known  examples  of  such  occurs  in  the  salivary  gland.  When, 
during  secretion,  the  arterioles  are  greatly  dilated,  a  pulse  may 
be  witnessed  in  the  veins  into  which  the  capillaries  open  out, 
owing  to  diminution  in  the  resistance  which  usually  is  suffi- 
ciently great  to  obliterate  the  pulse-wave. 

PsyudogioaL — In  severe  cases  of  heart-disease,  owing  to 
cardiac  dilatation  or  other  conditions,  giving  rise  to  incompe- 
tency of  the  tricuspid  valves,  there  may  be  with  each  ventricu- 
lar systole  a  back-flow,  visible  in  the  veins  of  the  neck. 
A>^  A  venous  pulse  is  a  phenomenon,  it  will  be  evident,  that 
always  demands  special  investigation.  It  means  that  the  usual 
bounds  of  nature  are  for  some  good  reason.being  over^stepped. 

Oomparatlti. — Before  entering  on  the  consideration  of  j^ue- 
nomenathat  all  are  agreed  are  purely  vital^we  call  attention  to 
the  circulation  in  forms  lower  than  the  mammal,  in  order  to 
give  breadth  to  the  student's  views  and  prepare  him  for  the 
special  investigations,  which  must  be  referred  to  in  subsequent 
chapters ;  and  which,  owing  to  the  praviou^  narrow  limits  (re- 
searches upon  the  frog  and  a  few  well-known  mammals)  having 
at  last  been  overleaped,  have  opened  up  entirely  new  aspects  of 
cardiac  phy8iology-H>ne  might  almost  say  revolutionized  the 
subject. 


X-lV^  .  .  ■sn^'^T*^:;!^  '.v,'; 


252 


ANIMAL   PHYSIOLOGY. 


h 


Owing  to  the  limitations  of  our  space,  the  references  to  lower 
forms  must  be  brief. 

We  recommend  the  student,  however,  to  push  the  subject 
further,  and  especially  to  carry  out  some  of  the  experiments  to 
which  attention  will  be  directed  very  shortly. 

In  the  lowest  organisms  (Infuaorians)  represented  by  Amoe- 
ba, Vorticella,  etc.,  there  are,  of  course,  no  circulatory  organs, 
unless  the  pulsating  vaf:'aoief:  of  some  forms  mark  the  crude 
beginnings  of  a  heart.  It  w  ill  be  bomo  in  mind,^  however,  that 
there  is  a  constant  streaming  of  the  protoplasm  itself  within 
the  organism. 

Among  Goelenterates  (Figs.  254, 255)  the  digestive  system,  as 
yet  but  imperfectly  developed,  seems  to  embody  in  itself  a  sort 
of  combination  of  the  functions  of  the  preparation  and  distribu- 
tion of  elaborated  food ;  and  it  is  worth  while  to  note  that  even 
in  the  highest  animals  the  digestive  tract  remains  in  close  con- 
nection with  the  circulatory  system. 

The  heart  is  first  represented,  as  in  worms,  by  a  pulsatile 
tube,  which  may,  as  in  the  earth-worm,  extend  throughout  the 
greater  part  of  the  length  of  the  animal,  and  has  usually  dorsal 
and  ventral  and  transverse  connections. 

The  dilatations  of  the  transverse  portions  in  one  division 
{metamere)  of  the  animal  seem  to  foreshadow  the  appearance  of 
auricles. 

The  pulsation  of  the  dorsal  vessel  in  a  large  earth-worm  is 
easy  of  observation. 

In  the  mollusks  the  heart  consists  of  a  ventricle  and  one  or 
more  auricles,  and  these  chambers  give  off  and  receive  large 
vessels  (Fig.  227). 

These  hearts  may  be  observed  ptdsating  with  the  naked  eye 
or  a  lens  in  the  clam,  oyster,  or  snail,  and  are  to  be  looked  for 
in  the  first  two  on  the  side  of  the  animal  toward  the  hinge  of 
the  shell. 

It  is  worthy  of  note  that  in  cephalopod  mollusks  (Cuttle- 
fish, Poulpe)  there  are  branchial  hearts,  which  may  be  re- 
garded in  the  light  of  pulsatile  venous  expansions,  a  remnant, 
perhaps,  of  conditions  found  in  lower  forms,  in  which  we  have 
seen  that  the  rhythmically  contracting  tube  plays  a  prominent 

In  amphioxus,  which  is  often  instanced  as  the  lowest  verte- 
brate, the  blood-vessels,  including  the  portal  vein,  are  pulsatile, 
while  there  is  no  distinct  and  separate  heart ;  but,  in  connection 
with  the  above  observations  in  cephalopods,  it  is  to  be  r** 


THE  CIRCULATION  OP  THE  BLOOD. 


868 


mces  to  lower 

h  the  subject 
xperiments  to 

ited  by  AmoB- 
latory  organs, 
»rk  the  crude 
however,  that 
itself  within 

iive  system,  as 
In  itself  a  sort 
1  and  distribu- 
note  that  even 

8  in  close  con- 
by  a  pulsatile 
hroughout  the 
usually  dorsal 

n  one  division 

9  appearance  of 

earth-worm  is 

cle  and  one  or 
i  receive  large 

1  the  naked  eye 
>  be  looked  for 
•d  the  hinge  of 

jUusks  (Cuttle- 
ch  may  be  re- 
ons,  a  remnant, 
which  we  have 
lys  a  prominent 

he  lowest  verte- 

in,  are  pulsatile, 

at,  in  connection 

it  is  to  be  r*- 


marked  that  in  this  creature  there  are  contractile  dilatations  at 
the  bases  of  the  branchial  arteries. 


"^Ai  y<! 


ory  orgaaa  o«  the  cuttle-<M>  (Siipfa  oAeJuoUf),  trfewed  from 
).  B^t^lm ;  C,  wntride :  ^o  Hid  Jo',  Mtwior  and  poate- 
V&,  M^Mlor  Teuk  «ink :  re",  iwrtntor  ym^  '^Zt^i  "^ 
KJr,  advriieiit  brMwhtel  TC«da  (htmnchm  •rterjM) ;  Kh, 
of  tlM  Mme ;  At,  AV,  MiriclM  reoeirlng  the  revebent 


Fia.  Mf7.— Circulatory  and 
the  donal  aide  (aftei 
rior  aorta ;  V.  lateral 
appendasea  of  the  veius; 
branchial  heart;  Ap,  a|  " 
branchial  yvm»\»  (branc 

In  some  Ascidians  the  heart  is  of  a  somewhat  crescentic 
form,  and  has  the  remarkable  property  of  beating  for  a  time  in 
one  direction,  then  stopping  and  reversing  its  rhythm.  In  a 
transparent  specimen,  under  the  microscope,  this  can  be  seen 

admirably. 

In  the  crab  the  heart  lies  within  a  pericardium,  loosely  at- 
tached, the  main  vessels  being  connected  with  the  pericardium 
and  not  directly  with  the  heart.  The  heart  sucks  its  blood 
from  the  pericardial  cavity  through  four  valvtdar  openings. 

In  such  a  creature  as  the  scorpion  there  is  a  chambered 
heart,  with  a  division  for  each  principal  segment  of  the  animal's 

body  (Fig.  308). 

While  in  moUusks,  crustaceans,  and  other  groups,  the  vas- 
cular system  does  not  form  a  connected  whole,  the  scorpion  is 
exceptionally  advanced  in  this  respect,  being  provided  with 
capillaries,  or  tubes  closely  representing  them.  Among  most 
of  the  invertebrates  the  blood,  after  leaving  the  arteries,  passes 
into  rather  wide,  irregular  spaces  among  the  various  tissues, 
from  which  it  is  taken  up  by  the  veins  without  the  intervention 
of  an  intermediate  set  of  vessels. 

The  circulatory  system  of  an  insect  or  crustacean  may  be 

i 


k'jM>Wiwwi«w'^i^''W'*M»**i«iiiuii.iiMii'WW4iiiJUWW*  iwa»w 


1^^— -  — 


354 


ANIM/L  PHYSIOLOOT. 


viewed  microscopically  i  a  aquatic  forms,  which  are  often  quite 
transparent,  especially  i  a  the  larval  condition. 


Although  the  respiratory  system  will  be  treated  from  the 
comparative  point  of  view,  the  student  will  do  well  to  note  now 


t'mmiimmmmm 


r 


^, 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


1.0     V^  1^ 


FhotograiJlic 

Sdenoes 

Carporatioii 


as  WIST  MAM  STRHT 

WnSTII,N.Y.  14SI0 

(7l«)l7a>4S03 


-  i^wfiBI 


r 


x 


CIHM/ICMH 
Collection  de 


■-\fmtasfm 


266 


ANIMAL  PHYSIOLOGY. 


k 


-^  Passing  on  to  the  vertebrates,  in  the  lowest  group,  the  fishes, 
the  heart  consists  of  two  chambers,  an  auricle  and  a  ventricle, 
the  latter  being  supplemented  by  an  extension  {bulbu8  arterio- 
stu)  pulsatile  in  certain  species;  and  an  examination  of  the 
course  of  the  circulation  will  show  that  the  heart  is  through- 
out venous,  the  blood  being  oxidized  in  the  gills  after  leaving 
the  former. 

Among  the  amphibians,  represented  by  the  frog,  there  are 
two  auricles  separated  by  an  almost  complete  septum,  and  one 


A^f 


f^ 


rw. 


FM 


Fto. 


.  ni-TlMfNK^heMt,  wen  from  llMfKmL  the  MTtieandMoCtteMt  rite  Iwv<i« 
nniMTed.   «  »  4.)  M,  oMottd ;  cbI,  CMoUd  gItaA ;  ao.  Mrt* ;  omMH^  Miriole  iaur^ 
leftaurMe;  sr.e,traMMnkMpiBHor:|>t.«,TeMc*nkbU(8riar;j».ei(,  pofaiMMMUiMaiH 
tniiik^r,tnuiciNaitMfc)MM;«.vMrtride(Ho«rca).    ^  _.      .  .j      _  v      .•„ 

no.  ■S.-neiMn^MwlMmMiiiid,tlwitauNT«MMMlw«lv  bMBopca^ 

rimhMiricalw  vahM.   (In  I.)  p.«,imlinoMur]r  v^b;  t.«,  rimavcwMiM;  «a'',ria»«u- 
rieotorTidTe.   oSiar  MMfaMt  •■  in  ■%•  Mi  (Howw). 

ventricle  characterised  by  a  spongy  arrangement  of  the  mus- 
cle-fibers of  its  walla. 

In  the  reptiles  the  division  between  the  auricles  is  complete, 
and  there  is  dne  ventricle  which  shows  imperfect  subdivisions. 

In  the  crocodile,  however,  the  heart  consists  of  four  per- 
fectly divided  chambers.  Of  the  two  aortic  arches,  one  arises 
together  with  the  pulmonary  artery  from  the  right  ventricle, 
and,  as  it  ciosses  over,  the  left  communicates  with  it* by  a  small 
opening,  so  that,  although  the  arterial  and  the  venous  blood 
are  completely  separated  in  the  heart,  they  intermingle  outside 
of  this  organ. 

In  birds  the  circulatory  system  is  substantially  the  same  as 
in  mammals ;  but  in  all  vertebrate  forms  below  birds  the  blood 
distributed  to  the  tissues  is  imperfectly  ozidiiied  or  is  partially 
venous. 


^  \ 


roup,  the  fishes, 
ind  a  ventricle, 
bfdbus  arterio- 
tination  of  the 
at  is  through- 
8  after  leaving 

frog,  there  are 
Bptum,  and  one 


»  hft  itde  Iwvf ng  beea 

heU,  IMfalMMMUlMaiH 

opHMd  up  to  ihow  the 
nmemm ;  va",  rimi-Mi- 


at  of  the  mus* 

sles  is  complete, 
ct  subdivisions, 
ts  of  four  per- 
■ches,  one  arises 
right  ventricle, 
th  it' by  a  small 
6  venous  blood 
rmingle  outside 

illy  the  same  as 
birds  the  blood 
d  or  is  partially 


THE  Cl&CULATION  OF  THE  BLOOD.  367 

As  an  example  of  the  influence  of  valves  and  of  blood-press- 
ure on  the  distribution  of  the  blood  we  may  take  the  case  of  the 
turtle,  in  which  the  subject  has  been  most  carefully  studied. 


..«« 


iio. 


m' 


v7,. 


nkt 


{Ul 


•»r.*V 


7*/ 


Fu>.  tM.-TlM  hMrt,  dtane 
tricoIirTahrw  havtac 
tha r^    ^  — 

«ai«»;  A. «, 

~  ;  MctleHali] 
olriiiiktlnii  (iftw  J 


Fw.  MB, 

ftoM  tiw  front,  the  Tentral  wall  and  one  of  the  Miricnlo-Ten- 
'    (1  M  &)  The  rod,  peMring  (ram  the  ventricle  Into 


«.J».«^.' 


W  Ivthe  blood  flowinc  wo  the  oerotid  nnd  aortic 
t»MVBtrjat  iwlmowary  Vein ;  va",  linitwirtaalar 
wtfi  — rhiile  witflenlir  val**;  «a.  «,  eeaifchmar 
'  vaHe  (aeiitiiin)  a(  {qrlanftani ;  p.  CM',  point  of 


SfklSL' 


»<bM).    r. 


.  __, .._jt.  and  I, left anride;  e, carotid artanr; 


The  structure  of  the  heart  and  the  relations  of  its  main  ves- 
sels, etc.,  will  probably  be  sufficiently  dear  upon  an  examina- 
tion of  the  accompanying  figures  and  the  descriptions  beneath 
them. 

The  right  and  left  auricles  pour  their  blood,  kept  somewhat 
apart  by  valves,  into  th^  ooMim  veno9um. 

Two  arterial  arches  arise  from  the  right-hand  part  of  this 
region,  while  the  pulmonary  artery  is  n  branch  carrying  ofl! 
blood  to  the  lungs  from  the  eavum  putmcne.  No  vessels  arise 
from  the  ootmm  turteriotfMn. 

Since  the  blood  flows  in  the  direction  of  least  resistance 
when  the  ventricle  contracts,  the  venous  blood  of  the  cavum 
venoeum  passes  on  into  the  pulm<nkary  artery  in  which  the 
pressure  is,  of  course,  lower  than  in  the  aortic  arches,  bbt,  as 
Uie  sjrstole  continues,  the  arteriikl  blood  of  the  cavum  arterio- 
W 


msmsswmmsgsm 


258 


ANIMAL  PHYSIOLOGY. 


sum  crowds  on  the  venous  blood  and  passes  itself  with  some  of 
the  darker  blood  into  the  aortic  vessels,  in  which  the  arrange- 


Iino.S3B. 


Ito.MB'. 


ment  of  the  valves  assiste  materially.  Note  that,  as  t^  »y^;^J« 
Xm^es,the  imperfect  septum  ^*rfV»^!,?^^tT.^ 
Sd  cavum  venosum  approaches  the  back  of  *1^«^J«^;^*?;"^* 
^us  tends  to  shut  off  ttxe  cavum  pulmone  '«>"?  ^^^'^'^^ 
As  a  result  of  the  entire  arrangement,  the  least  oximaea 
blo^^  to  the  lungs,  and  the  most  aSrated  to  the  head  and 

anterior  narte  of  the  animal.  _.    i.i„  „«,«. 

fe  the  frog  and  otheroreatures,  with  three  fanperfectlysepa. 

rated  heart  cavities,  a  similar  result  is  attained. 

"^^^!L^  in  »*  r"  t.  the  '»^.  .7^^" 
iMmmato,  iiiclodtog  man,  wiU  b*  «w>M«it,  Md  xt  la  en«o»liy 


•aaf 


THE  GIBCULATIOM  OF  THE  BLOOD. 


S69 


lelf  with  some  of 
lich  the  arrange- 


]L.X 


idlp,MR|iid- 
BOSarOagMi- 

C.  V,  oSmm  vnomim.   C.  p. 
fj.   B.AO,. 


ithat,a8thesyetole 
)  cavum  pulmonum 
:  the  heart  wall,  and 
om  the  purer  blood. 
,the  least  oxidiaed 
bted  to  the  head  and 

ee  imperfectly  aepa^ 

ined. 

fo^al  conditions  in 
,  and  it  is  especially 


to  be  observed  that  in  the  case  of  the  foetus  and  these  lower 
groups  of  vertebrates  the  brain  and  anterior  parts — that  is, 
the  most  important  portions  of  the  animal  functionally, 
the  parts  on  which  the  rest  depend  for  their  well-being  (since 
the  brain  is  the  seat  of  all  the  main  directive  centers)— are 
fed  with  the  best  blood  the  organism  possesses,  a  fact  which 
probably  explains  in  part  the  relatively  large  size  of  these 
portions  of  the  body  early  in  foetal  life  and  throughout  its 
duration. 

We  now  urge  upon  the  student  the  importance  of  making 
some  observations  for  himself  upon  the  heart  of  the  frog,  tur^ 
tie,  snake,  fish,  or  other  of  the  cold-blooded  animals.  At- 
tention should  be  given  chiefly  to  the  functions  of  the  heart, 
though  to  do  this  intelligently  it  must  be  preceded  by  some 
study  of  the  anatomy  of  the  organ.  It  will  be  understood  that 
any  directions  we  may  give  for  the  manipulative  part  of  the 
work  will  be  of  the  simplest  kind,  and  rather  suggestive  of  the 
general  method  of  procedure  than  intended  to  illustrate  the 
best  methods. 

In  reality,  it  is  better  for  exact  investigation  of  the  heart 
that  no  auffisthetic  be  given,  and  an  animal  may  be  rendered 
insensible  by  a  sudden  blow  upon  the  head,  which,  as  we  shall 
show  later,  may  be  painless.  However,  it  will  be,  upon  the 
whole,  perhaps,  best  that  the  animal  be  given  a  few  whiffs  of 
dther  beneath  some  (glass)  vessel,  and  as  soon  as  it  becomes 
insensible,  to  withdraw  the  aneesthetic,  remove  or  crush  the 
head  (brain),  so  that  throughout  the  investigation  there  may 
be  neither  interference  with  the  heart  from  this  organ  nor  any 
doubt  about  the  animal's  insensibility. 

It  is  well  to  open  the  abdomen  a  little  below  the  heart,  so 
that  the  latter  may  be  exposed,  with  its  pericardium  intact, 
when  the  relations  of  the  l-aati  to  the  surrounding  parts  may 
be  noticed. 

What  strikes  every  observer  is  the  sluggish  action  of  the 
hearts  of  these  animals— a  great  advantage  in  attenvpting  to 
estimate  roughly  the  relative  time  occupied  by  the  systole  and 
diastole,  of  the  different  chambers;  the  peculiar  vermiform 
nature  of  the  contraction;  the  changes  of  color  dependent  on 
the  degree  to  which  any  chamber  is  filled  with  blood;  and 
many  of  those  minor  details  important  in  nwking  up  a  total 
general  impression,  but  not  readily  expressed  in  words. 

After  the  animal  has  been  bled,  the  heart's  action  may  still 
be  profitably  studied;  and,  finally,  it  may  be  learned  that  the 


iSlifiiHf 


900 


ANIMAL  PHTSIOLOOT. 


V 


heart  will  pulsate  when  removed,  either  entire  or  after  being 
divided  into  sections. 

In  another  specimen  it  would  be  desirable  to  allow  the 
heart,  to  be  kept  bathed  in  serum  or  physiological  saline  solu< 
tion,  to  beat  as  long  as  it  will,  and  to  note  the  various  phases 
of  irregularity,  weakening,  and  cessation  of  action  in  its  dif- 
ferent parts. 

It  is  also  highly  instructive  to  observe  the  effect  of  ligating 
off  certain  of  the  chambers  from  the  rest  of  the  organ.  * 

Any  one  who  makes  a  few  such  observations  will  be  pre- 
pared to  comprehend  readily  any  of  the  experiments  on  ,the 
hearts  of  the  cold-blooded  animals,  and  will  be  able,  especially 
if  he  has  followed  out  earlier  recommendations  as  to  the  study 
of  the  heart  of  the  xdammal,  to  form  a  mental  picture  of  what 
is  transpiring  within  his  own  breast,  which  is  one  of  the  most 
dosirable  accomplishments — ^in  fact,  the  best  test  of  real  knowl- 
edge. 

Whatever  ground  for  differences  of  opinion  there  may  be 
as  to  the  extent  to  which  the  phenomena  we  have  as  yet  been 
describing  are  mechanical  in  their  natiure,  all  are  agreed  that 
such  explanations  are  insufficient  when  applied  to  the  facts 
witb  which  we  have  yet  to  deal  They,  at  all  events,  can  be 
regarded  only  as  the  result  of  vitality. 

C^lien  one  reflects  upon  the  vicissitudes  through  which  an 
animal  must  pass  daily  and  hourly,  necessitating  either  that 
they  be  met  by  modified  action  of  the  organs  of  the  body  or 
that  the  destruction  of  the  organism  ensue,  it  becomes  clear 
that  the  varying  nutritive  needs  of  each  pait  must  be  met  by 
changes  in  the  circulatory  system.  These  changes  may  affect 
any  part  of  the  entire  arrangement,  and  it  rarely  happens,  as 
will  appear,  that  one  part  is  modified  without  a  correspond- 
ing one,  very  frequently  of  a  different  kind,  taking  place  in 
some  other.  What  these  various  correlated  modifications  are, 
and  how  they  are  brought  about,  we  shall  now  atten^pt  to 
describe,  and  it  will  greatly  assist  in  the  comprehension  of  the 
whole  if  the  student  will  endeavor  to  keep  a  clear  mental  pict- 
ure of  the  parts  before  his  mind  throughout,  using  the  figures 
and  verbal  descriptions  only  to  assist  in  the  construction  of 
such  a  mental  image.  We  shall  begin  with  the  vital  pump— 
the  heart. 


■mrr 


■  L.,  ,  .m..!tiU.,..,UU.a.tL.  .-  ■JL-' 


THE  CIBCULATION  OF  THE  BLOOD. 


261 


3  or  after  being 

lie  to  allow  the 
rical  saline  solu- 
a  various  phases 
iction  in  its  dif- 

effect  of  ligating 
le  organ.  * 
ions  will  be  pre- 
leriments  on  ,the 
M  able,  especially 
IS  as  to  the  study 
il  picture  of  what 
B  one  of  the  most 
«st  of  real  knowl- 

ion  there  may  be 
)  have  as  yet  been 
11  are  agreed  that 
plied  to  the  facts 
all  events,  can  be 

through  which  an 
itating  either  that 
ms  of  the  body  or 
e,it  becomes  clear 
li  must  be  met  by 
changes  may  affect 
rarely  happens,  as 
hout  a  correspond- 
id,  taking  place  in 
1  modifications  are, 
ill  now  attempt  to 
>mprehension  of  the 
a  clear  mental  pict- 
it,  using  the  figures 
the  construction  of 
th  the  vital  pump— 


Thk  Beat  of  the  Heart  and  its  Modifications. 

As  has  been  already  noted,  the  cardiac  muscle  has  features 
peculiar  to  itself,  and  occupies  histologically  an  intermediate 
place  between  the  plain  and  the  striped  muscle-cells,  and  that 
the  contraction  of  the  heart  is  also  intermediate  in  character, 
and  is  best  seen  in  those  forms  of  the  organ  which  are  some- 
what tubular  and  beat  slowly.  But  the  contraction,  though 
peristaltic,  is  more  rapid  t<han  is  usually  the  case  in  other 
organs  with  the  smooth  form  of  muscle-fiber. 

The  heart  behaves  under  a  stimulus  in  a  peculiar  manner. 
The  effect  of  a  single  induction  shock  depends  on  the  phase  of 
contraction  in  which  the  heart  is  at  the  moment  of  its  applica- 
tioi\f  Thus  at  the  commencement  of  a  systole  there  is  no  visi- 
ble effect,  while  beats  of  unusual  character  result  at  other 
times.  But  tetanus  can  not  be  induced  by  any  form  or  method 
of  stimulation.    The  latent  period  of  cardiac  muscle  is  long. 

In  a  heart  at  rest  a  single  stimulus  (as  the  prick  of  a  needle) 
usually  calls  forth  but  one  contraction. 

The  Nervous  System  in  Relation  to  the  Heart. 

^he  attempts  to  determine  just  why  the  heart  beats  at  all, 
and  especially  the  share  taken  by  the  nervous  system,  if  any 
direct  one,  are  beset  with  great  difficulty ;  though,  as  we  shall 
attempt  to  show  later,  this  subject  also  has  been  cramped  within 
too  narrow  limits,  and  hence  regarded  in  a  false  light. 

Till  comparatively  recently  the  frog's  heart  alone  received 
much  attention,  if  we  except  tiiioee  of  certain  well-known  mam- 
mala  In  the  heart  of  the  frog  there  are  ganglion-cells  in  vari- 
ous parts,  especially  numeroufi  in  the  sinus  venosus  (or  expan- 
sion of  the  great  veins  whero  tbey  meet  the  auricles) ;  also  in 
the  auricles,  more  especially  •  ■  ^be  septum  (ganglia  of  Bemak), 
while  they  are  absent  from  th  greater  part  of  the  ventricle, 
though  found  in  the  auriculo- ventricular -groove  (ganglia  of 
Bidder). 

Recently  it  has  been  found  that  ganglion-cells  occur  in  the 
ventricles  of  warm-blood  animals.  In  the  hearts  of  the  dog, 
calf,  sheep,  and  pig,  which  are  those  lately  subjected  to  investi- 
gation, it  is  found  that  the  nerve-cells  do  not  occur  near  the 
apex  of  the  ventricles,  but  mainly  in  the  middle  and  basal  por- 
tions, being  most  abundant  in  the  anterior  and  posterior  inter- 
ventricular furrows  and  in  the  left  ventricle.    But  there  are 


liiiiiH 


368 


ANIMAL  PHTSIOLOOT. 


differences  for  each  group  of  animals;  thus,  these  ganglion- 
cells  are  most  abundant,  so  far  as  the  mammals  as  yet  inves- 
tigated are  concerned,  in  the  ventricles  of  the  pig,  and  least  so 
in  those  of  the  dog.  In  the  cat  they  are  also  scanty.  Oanglion- 
cells  occur  in  the  auricles,  and  are  especially  abundant  near  the 
terminations  of  the  great  veins. 

It  has  long  been  known  that  the  heart  of  a  frog  removed 
from  the  body  will  pulsate  for  hours,  especially  if  fed  with 
serum,  blood,  or  similar  fluids;  and  that  it  may  be  divided  in 
almost  any  conceivable  way,  even  when  teased  up  into  minUte 
particles,  and  still  continue  to  beat.  The  apex,  however,  when 
separated  does  not  beat.  Ttt  even  this  quiescent  apex  may  be 
tot  pulsating  if  tied  upon  the  end  of  a  tube,  through  which  it 
may  be  fed  under  pressure. 

We  may  here  point  out  that  the  whole  heart  or  a  part  of  it 
may  be  made  to  describe  its  action  by  ihe  graphic  method  in 
various  ways,  the  principles  underlying  which  are  either  that 
the  heart  pulls  upon  a  recording  lever  (lifts  it)  acts  against  the 
fluid  of  a  manometer ;  or,  inclosed  in  a  vessel  containing  oil  or 
similar  fluid,  moves  a  piston  in  a  cylinder. 

It  has  also  long  been  known  that  a  ligature  drawn  around 
the  sinus  venoeus  (in  the  frog)  at  its  junction  with  the  auricles 
stopped  the  heart  for  a  certain  period,  and  this  experiment  (of 
Stanniua)  was  thought  to  demonstrate  that  the  heart  was  ar- 
rested becatise  the  nervous  impulses  proceeding  to  the  ganglion- 
cells  along  the  cardiac  nerves  or  ganglia  of  this  region  were 
cut  off  by  the  ligature ;  in  other  words,  the  heart  ceased  to  beat 
because  ibe  outside  machinery  on  which  the  action  of  the  inner 
depended  was  suddenly  disconnected.  Other  explanations  have 
been  offered  of  this  fact. 

^ithin  the  last  few  years  great  light  has  been  thrown  upon 
the  whole  subject  of  cardiae  physiology  in  consequence  of  in- 
vestigators having  studied  the  hearts  of  various  cold-blooded 
animals  and  of  several  invertebrates.  The  hearts  of  the  Che- 
loniana  (tortoises,  turtles)  have  received  special  attention,  and 
their  investigation  has  been  fruitful  of  results,  to  the  general 
outcome  of  which,  as  well  as  those  accruing  from  recent  com- 
parative studies  as  a  whole,  we  can  alone  refer. 

Very  briefly,  the  following  are  some  of  the  main  facts : 

1.  In  all  cold-blooded  animate  the  order  in  which  the  sub- 
divisions of  the  heart  cease  to  pulsate  when  kept  under  the 
same  conditions  is  invariable,  viz.,  ventricle,  auricles,  sintis. 

d.  The  sinus  and  auricles^  when  separated  by  section,  Hga* 


THB  CIBCULATION  OF  THB  BLOOD. 


968 


these  ganglion- 

as  yet  inves- 

)ig,  and  least  so 

mty.  Ganglion- 

jnndant  near  the 

a  frog  removed 
[ially  if  fed  with 
y  be  divided  in 
np  into  minilte 
«,  however,  when 
cent  apex  may  be 
through  which  it 

«rt  or  a  part  of  it 
ipraphic  method  in 
ch  are  either  that 
it)  acts  against  the 
il  containing  oil  or 

tnre  drawn  around 
n  with  the  auricles 
this  experiment  (of 
b  the  heart  was  ar- 
ing  to  the  gangUon- 
t>f  this  region  were 
beart  ceased  to  beat 
>  action  of  the  inner 
r  explanations  have 

s  been  thrown  upon 
,  consequoice  of  in- 
arious  cold-blooded 
9  hearts  of  the  Che- 
wcial  attention,  and 
suits,  to  the  general 
g  from  recent  com- 
)fer. 

the  main  facts : 
ir  in  which  the  sub- 
lien  kept  under  the 
B,  auricles,  sinus. 
Aed  by  section,  Hgar 


ture,  or  otherwise,  either  together  or  singly,  continue  to  beat, 
whether  amply  provided  with  or  surrounded  by  blood. 

8.  The  ventricle  thus  separated  displays  less  tendency  to 
beat  independent  of  some  stimulus  (as  feeding  under  pressure), 
though  a  very  weak  one  usually  suffices — i.  e.,  its  tendency  to 
spontaneous  rhythm  is  less  marked  than  is  the  case  with  the 
other  parts  of  the  heart.  These  remarks  apply  to  the  hearts 
of  Chtioniana — ^fishes,  snakes,  and  some  other  cold-blooded 
animals. 

4.  In  certain  fishes  (skate,  ray,  shark)  the  beat  may  be.  re* 
versed  by  stimulation,  as  a  prick  of  the  ventricle.  This  is 
accomplished  with  more  difficulty  in  other  cold-blooded  animals, 
and  still  more  so  in  the  mammaL 

6.  In  certain  invertebrates,  notably  the  F&ulpe  (Octopus),  a 
careful  search  has  revealed  no  nerve^sells,  yet  their  hearts  con- 
tinue to  beat  when  their  nerves  are  severed,  on  section  of 
parts  of  the  organ,  etc. 

6.  A  strip  of  the  muscle  from  the  ventricle  of  the  tortoise, 
when  placed  in  a  moist  chamber  and  a  current  of  electricity 
passed  through  it  for  some  hours,  will  commence  to  pulsate  ai^ 
continue  to  do  so  after  the  current  has  been  withdrawn;  and 
this  holds  when  the  strip  is  wholly  free  from  nerve-cella 

From  the  above  facts  certain  inferences  have  been  drawn : 
1.  It  has  been  concluded  that  the  sinus  is  the  originator  and 
director  of  the  movements  of  the  rest  of  the  heart.  2.  That  this 
is  owing  to  the  ganglia  in  its  walls.  While  all  recognize  the 
importance  of  the  sinus,  some  physiologists  hold  to  the  gangli- 
onic influence  as  essential  to  the  heart-beart,  still ;  while  others, 
influenced  by  the  facts  mentioned  above,  are  disposed  to  regard 
them  as  of  very  doubtful  importance — at  all  events,  as  origina- 
tors of  the  movements  of  the  heart 

The  tendency  now  seems  to  be  to  attach  undue  importance 
to  the  spontaneous  contractility  of  the  heart-muscle;  for  it  by 
no  means  follows  logically  that,  because  a  muscle  treated  by 
electricity,  when  out  off  from  the  usual  nerve  influence  that  we 
believe  is  being  constantly  exerted  on  the  heart  like  other  or- 
gans, will  contract  and  continue  to  do  so  in  the  absence  of  the 
stimulus,  it  does  so  normally;  or,  because  some  hearts  beat  in 
the  absence  of  nerve-cells,  that  therefore  nerve-cells  are  of  no 
account  in  any  case.  Such  views,  when  pressed  to  the  extreme, 
lead  to  as  narrow  conceptions  as  those  they  are  intended  to  re- 
place. 

Taking  into  account  the  facts  mentioned  and  others  we  have 


M4 


ANIMAL  PHTtUOLOOT. 


not  space  to  enumerate,  we  submit  the  following  as  a  safe  view 
to  entertain  of  the  beat  of  the  heart  in  the  light  of  our  present 
knowledge : 

Recent  investigations  show  clearly  that  there  are  great  dif- 
ferences in  the  hearts  of  animals  of  diverse  groups,  so  that  it 
is  not  possible  to  speak  of  "the  heart"  as  though  our  remarks 
applied  equally  to  this  organ  in  all  groups  of  animals. 

(It  must  be  admitted  that  our  understanding  of  the  hearts  of 
the  cold-blood  animals  is  greater  than  of  the  mammalian  heart ; 
while,  so  far  as  exact  or  experimental  knowledge  is  concerned, 
the  human  heart  is  the  least  understood  of  all,  though  there  is 
evidence  of  a  pathological  and  clinical  kind  and  subjective 
experience  on  which  to  base  conclusions  possessing  a  certain 
value ;  but  it  is  clear  to  those  who  have  devoted  attention  to 
(Comparative  physiology  that  the  more  this  subject  is  extended 
.the  better  prepared  we  shall  be  for  taking  a  broad  and  sound 
view  of  the  physiology  of  the  human  heart  and  man's  other 
organs. 

Whatever  may  be  said  of  the  invertebrates,  among  which 
greater  simplicity  of  mechanism  doubtless  prevails,  there  can 
be.no  doubt  that  the  execution  of  a  cardiac  cycle  of  the  htert 
in  all  vertebrates,  and  especially  in  the  higher,  is  a  very  com- 
plex .process  from  the  number  of  the  factors  involved,  their  in- 
teraction, and  their  normal  variation  with  circumstances;  and 
we  must  therefore  be  suspicious  of  any  theory  of  excessive  sim- 
plicity in  this  as  well  as  other  parts  of  physiology. 

We  submit,  then,  the  following  as  a  safe  provisional  view  of 
the  causation  of  the  heart-beat : 

1.  The  factors  entering  into  the  causation  of  the  heart-beat 
of  all  vertebrates  as  yet  examined  are :  (a)  A  tendency  to  spon- 
taneous contraction  of  the  muscle-cells  composing  the  organ ; 
(b)  intra-cardiac  blood-pressure;  (c)  condition  of  nutrition  as 
determined  directly  by  the  nervous  supply  of  the  organ  and  in- 
directly by  the  blood. 

3.  The  tendency  to  spontaneous  contraction  of  muscle-cells 
is  most  marked  in  the  oldest  parts  of  the  heart  (a  g.,  sinus), 
ancestrally  (phylogenetically)  considered. 

3.  Intra-oardiac  pressure  exercises  an  influence  in  determin- 
ing the  origin  of  pulsation  in  probably  all  hearts,  though  like 
other  factors  its  influence  varies  with  the  animal  group.  In 
the  moUusk  (and  allied  forms)  and  in  the  fish  it  seems  to  be  the 
controlling  factor. 

4.  We  must  recognize  the  power  one  cell  has  to  excite  when 


THE  CIRCULATION  OP  THE  BLOOD. 


866 


I  as  a  safe  view 
of  our  present 

re  are  great  dif- 
■oups,  so  that  it 
gh  our  remarks 
limals. 

of  the  hearts  of 
immaliau  heart ; 
{e  is  concerned, 
though  there  is 

and  subjective 
eesing  a  certain 
>ted  attention  to 
iject  is  extended 
>road  and  sound 
and  man's  other 

)s,  among  "which 
■evails,  there  can 
iycle  of  the  hbart 
Br,  is  a  very  com- 
Involved,  their  in- 
rcumstances;  and 
r  of  excessive  sim- 
logy. 
rovisional  view  of 

of  the  heart-beat 
tendency  to  spon- 
[KMBittg  the  organ ; 
>n  of  nutrition  as 

the  organ  and  in- 

Dn  of  muscle-cells 
leart  (a  g.,  sinus), 

lence  in  determin- 
earts,  though  like 
ikuimal  group.  In 
ti  it  seems  to  be  the 

has  to  excite  when 


in  action  neighboring  heart-cells  to  contraction.  The  abilityN 
that  one  protoplasmic  cell-mass  has  to  initiate  in  others,  under^ 
certain  circumstances,  like  conditions  with  its  own,  is  worthy  j 
of  more  serious  consideration  in  health  and  disease  than  it  has) 
yet  received. 

5.  The  influence  of  the  cardiac  nerves  becomes  more  pro- 
nounced as  we  ascend  the  animal  scale.  Their  share  in  the 
heart's  beat  will  be  considered  later. 

6.  Apparently  in  all  hearts  there  is  a  functional  connection 
leading  to  a  regular  sequence  of  beat  in  the  different  parts,  in 
which  the  sinus  or  its  representatives  (the  terminations  of  great 
veins  in  the  heart)  always  takes  the  initiative.  One  part  hav- 
ing contracted,  the  others  must  necessarily  follow ;  hence  the 
rapid  onset  of  the  ventricular  after  the  auricular  contraction  in 
the  mammal,  and  the  long  wave  of  contraction  that  seems  to 
pass  evenly  over  the  whole  organ  in  cold-blooded  animals. 

The  basis  of  all  these  factors  is  to  be  sought  finally  in  the 
Cn^iua:cdsorUiv^^^lja£.£xo^^  A  heart  in  its  most  devel- 

oped form  still  retains,  so  to  speak,  the  inherited  but  modifietl 
Amoeba  in  its  every  cell. 

Whether  the  intrinsic  nerve -cells  of  the  heart  take  any 
share  directty  in  the  cardiac  beat  must  be  considered  as  yet 
undetermined.  Possibly  they  do  modify  motor  impulses  from 
nerves,  while  again  it  may  be  that  they  have  an  influence  over 
nutritive  processes  only.  The  subject  requires  further  study, 
both  anatomical  and  physiological. 

Intlukncb  of  the  YAQvar  Nerve  upon  the  Heart. 

The  principal  facts  in  this  connection  may  be  stated  as  fol- 
lows, and  apply  to  all  the  animals  thus  far  examined : 

1.  In  all  cases  the  action. of  the  heart  is  modified  by  stimu- 
lation of  the  medulla  oblongata  or  the  vagus  nerve. 

2.  The  modification  may  consist  in  prompt  arrest  of  the 
heart,  in  slowing,  in  enf  eeblement  of  the  beat,  or  a  combination 
of  the  two  latter  effects^ 

3.  After  the  application  of  the  stimulation  there  is  a  latent 
period  before  the  effect  is  manifest,  and  the  latter  may  outlast 
the  stimulation  by  a  considerable  period. 

4.  In  most  animals  the  sinus  venosus  and  auricles  are  af- 
fected before  the  ventricles,  and  the  vagus  may  influence  these 
parts  when  it  is  powerless  over  the  ventricle. 

5.  After  vagus  inhibition,  the  action  of  the  heart  is  (almost 


AMIMAL  PHYSIOLOGY. 


jlMMilMM^^ 


JiUlJUUiMI 


naUngoa  it. 
foTAOoMider- 


we  may  «y  i^  *,  wki.,g  <»P«*»y  of  th«  h»rt  U  t™- 
porarily  increased.  .fficieDor  ol  the  heart  is  in  pro- 


attotilflttonViiOW. 


^.n  i.  feeble  "'■|;^-'^^^TJi^^pSJ^ttw1.^t 

in  proportion  to  its  needs.  ^Th»"  *  ^"^^      '^ 

de^rves  to  receive  »  8«^«r^^'!^^te  in  histological  altem- 

7.  Section  of  both  vag^  '^''^^JS^Z^i^eZion,  which 
tlonsintheheart'Bstmctu^,c^e^«»t^^^  ^^  ^^ 

strains  of  life. 


.,~>aia'>i"""*"' 


li 


THE  CIHCULATION  OF  THE  BLOOD. 


967 


:  variable,  but 
in  force. 


(AJliliUl/Ul/ 


TbbeNiid(romri«M 
nnieleTM'  ruKIng  on  It. 

■ToOMmd  iMteMMTMl 

k  It  iMtad  for  »  ooiMUer- 


le  heart  is  tem- 

j  heart  is  in  pro- 
1  cases  when  the 


\ 


rgmngv^ililo  001  re  darhred 

light  be  said  to  be 
nportant  law  that 

liistological  altera- 
)generation,  which 
ity  and  eicpoee  it 
tquently  recurring 


8.  In  the  cold-blooded  animals  the  heart  may  be  kept  at  a 
standstill  by  vagus  stimulation  till  it  dies,  a  period  of  hours 
(one  case  of  six  hours  reported  for  the  sea-turtle). 

9.  Certain  drugs  (as  atropine),  applied  directly  to  the  heart, 
or  injected  into  the  blood,  prevent  the  usual  action  of  the 
vagus. 

10.  During  vagus  arrest  the  heart  substance  undergoes  a 
change;  reisulting  in  an  unusual  dilatation  of  the  organ.  This 
may  be  witnessed  whether  the  heart  contains  blood  or  not. 

11.  The  heart  may  be  arrested  by  direct  stimulation,  espe- 
cially of  the  sinus,  and  at  the  points  at  which  the  electrodes  are 
applied  there  is  apparently  a  temporary  paralysis.  The  same 
alteration  in  the  beat  may  be  noticed,  as  when  the  main  trmik 
of  the  vagus  is  stimulated. 

12.  The  heart  may  be  inhibited  through  stimulation  of  vari- 
ous parts  of  the  body,  both  of  the  surface  and  internal  organs 
(reflex  inhibition). 

13.  One  vagus  being  divided,  stimulation  of  its  upper  end 
may  cause  arrest  of  the  heart. 

14.  Stimulation  of  a  small  part  of  the  medulla  oblongata 
will  produce  the  same  result,  provided  one  or  both  vagi  be 
intact. 

15.  Section  of  both  vagi  in  some  animals  (the  dog  notably) 
increases  the  rate  of  the  cardiac  beat.  The  result  of  section  of 
one  pneumogastrio  nerve  is  variable.  The  heart's  rhythm  is 
usufJly  to  some  extent  quickened. 

16.  During  vagus  inhibition  from  any  cause  in  mammals 
and  many  other  animals,  the  heart  responds  to  a  single  stimu- 
lus, as  the  prick  of  a  needle,  by  at  least  one  beat.  An  observer 
studying  for  himself  the  behavior  of  the  heart  in  several  groups 
of  animals  with  an  open  nund,  for  the  purpose  of  observing 
all  he  can  rarther  than  proving  or  disjnroving  some  one  point, 
becomes  strongly  impressed  with  the  variety  in  unity  that  runs 
through  cwrdiao  physiology,  including  the  influence  of  nerve- 
cells  (centers)  through  nerves;  for  it  will  not  be  forgotten  that 
normally  nerves  originate  nothing,  being  conductors  only,  so 
that  when  the  vagus  is  stimulated  by  us  we  are  at  the  most 
but  imitating  in  a  rough  way  the  wcKrk  of  central  nerve-cells. 
We  can  only  mentioiL  a  few  points  to  illustrate  this. 

In  the  frog  a  succession  of  light  taps,  or  a  single  sharp  one 
("Klopfversuch*'  of  Qolta),  wiU  usually  arrest  the  heart  re- 
flmdy;  though  somettmes  it  is  very  difficult  to  accomplish. 
But  in  the  fish  the  ease  with  which  the  heart  may  be  reflexly 


sefwjf! 


MRRKa 


flilWJBWWMliiiitwwjatutiwiwwiiiiwiiiyBWiiilBi^^ 


S168 


ANIMAL  PHYSIOLOGY. 


inhibited  bv  Kentle  stimtilation  of  almost  any  portion  of  the 
::S;^woXrfuL   Again,in  some  animals  the  vagus  arreBt. 


ItVacw. 


B«w(. 


Bmteabofvliadull*. 


^^-s^^sstssLSsss: 


^flgnBkNW'ra> 


y& 


AMwMita 


«h.  lieMt  for  oriy  .  brirf  period,  wh«  it  Vr»k.  .way  toto  !♦. 
ragna  inhibition— i.  ».,  It  *o«»  not  re»pono  w  •  u. 

•^^  ta  ™»jiy  .c««.to  ««i«  to  *«*  *';i!sin;; 


«<lili  Ki'fTii 


her  animals,  the 

loft  daring  the 

a  a  meohanioi^ 

le  heart  reoom- 

yentrioles) ;  hut 

animals.    It  it 


THB  CIRCULATION  OP  THE  BLOOD. 


269 


also  a  fact  that  in  most  of  the  cold-blooded  animals  the  right 
vagus  is  moriB  efficient  than  the  left,  owing,  we  think,  not  to  the 
nerves  themselves  so  much  as  to  their  manner  of  distribution 
in  the  heart — ^the  greater  jMrtion  of  the  driving  part  of  the 
organ,  so  to  speak,  being  supplied  by  the  right  nerve ;  for,  when 
even  a  small  part  of  the  heart  is  arrested,  it  may  be  overcome 
by  the  action  of  a  larger  portion  of  the  same,  or  a  more  domi- 
nant region  (the  sinus  mostly). 

OoMbuUnab— The  inferences  from  the  facts  stated  in  the 
above  paragraphs  are  these:  1.  There  is  in  the  medulla  a  col- 
lection of  cells  (center)  which  can  generate  impulses  that  reach 
the  heart  by  the  vagi  nerves  and  influence  its  muscular  tissue, 
though  whether  directly  or  through  the  intermediation  of 
nerve-cells  in  its  substance  is  imcertain.  It  may  possibly  be  in 
both  ways.  2.  This  center  (cardio-inhibitory)  may  be  influ- 
enced reflexly  by  influences  ascending  by  a  variety  of  nerves 
from  the  periphery,  including  paths  in  the  brain  itself,  as 
shown  by  the  influence  of  emotions  or  the  behavior  of  the 
heart.  3.  The  cardio-inhibitory  center  is  the  agent,  in  part, 
through  which  the  rhythm  of  the  heart  is  adapted  to  the  niBeds 
of  the  body.  4.  The  arrest,  on  direct  stimulation  of  the  heart, 
is  owing  to  the  effect  produced  on  the  terminal  fibers  of  the 
vagi,  as  shown  by  the  dilation,  etc,  corresponding  to  what 
takes  place  when  the  trunk  of  the  nerve  or  the  center  is  stimu- 
lated. 5.  The  quickening  of  the  heart,  following  section  of  the 
vagi,  seems  to  show  that  in  some  animals  the  inhibitory  center 
exercises  a  constant  regulative  influence  over  the  rhythm  of 
the  heart  6.  The  irritability  and  dilatability  of  the  cardiac 
tissue  may  be  greatly  modified  daring  vagus  inhibition.  Some- 
times this  is  evident  before  the  rhythm  itself  is  appreciably 
altered.  7.  The  heart-musole  has  a  latent  period,  like  other 
kinds  of  muscle;  and  cardiac  effects,  when  initiated,  last  a 
variable  period. 

There  are  many  other  obvious  conduirions,  which  the  stu- 
dent will  draw  for  himself. 

But  a  question  arises  in  regard  to  the  significance  of  the 
cardiac  arrest  under  these  oiroumstaBoes,  and  the  altered  action 
that  follows.  The*fact  that,  when  the  heart  is  severed  from  the 
central  nervous  system  by  section  of  its  nerves,  profound 
changes  in  the  minute  structure  of  its  calls  ensue,  points  un- 
mistakably to  some  nutritive  influence  that  must  have  operated 
through  the  vagi  nerves.  That  stimulation  of  the  vagus  re- 
stores regularity  of  rhythm  and  strengthens  the  beat  of  the 


MNi 


wmm 


mmmmm 


270 


ANIMAL  PHTSIOLOOT. 


failing  heart,  is  also  very  saggestive.  That  many  diaorden  of/ 
the  heart  are  (Soincident  with  periods  of  mental  anguish  or) 
worry,  and  that  in  certain  cases  of  severe  mental  application^ 
the  heaif  8  rhythm  has  become  very  slow,  also  point  to  influ- 
enpes  of  a  central  origin  as  greatly  affecting  the  lif e-processesj 
of  this  orgai^.     ^ 

It  has  been  shown  that  the  vagns  nerve  in  some  cold-blooded 
animals,  as  is  probable  also  in  the  higher  vertebrates,  oonaiata 
of  two  seta  of  fibers— 4ho»e  which  ore  inhibitory  proper  and 
those  which  are  not,  bid  bdong  to  the  sympathetic  system. 

Separate  stimulation  of  the  former  favors  nutritive  pro- 
cesses, is  preservative;  of  the  latter,  destructive.  This  has 
been  expressed  by  saying  that  the  former  fevors  constructive 
(anabolic)  metabolism;  the  latter  destructive  (katabolic)  me- 
tabolism. It  is  assumed  that  all  the  metabolism  of  the  body 
may  be  represented  as  made  up  of  katabolic  following  anabolic 
processes. 

Whether  such  a  view  of  metabolism  expresses  any  more 
than  a  sort  of  general  tendency  of  the  chemistry  of  the  body 
is  doubtful.  It  is  a  very  simple  representation  of  what  in  all 
probability  is  extremely  complex;  and  if  it  be  implied  that 
throughout  the  body  certain  steps  are  always  taken  upward  in 
construction  to  be  always  itfterwards  followed  by  certain  down- 
ward destructive  dianges,  we  must  reject  it  as  too  rigid  and 
artificial  a  representation  of  natural  processes 

We  thjnk,  however,  that,  upon  all  the  evidence,  i>athological ' 
and  clinical  as  well  as  physiological,  ^e  student  may  believe^ 
that  the  vagus  nerve,  like  the  other  nerves  of  the  body,  accord- 
ing to  our  own  theory,  exercises  a  constant  beneficial,  guiding^ 
—let  us  say  determining— influence  over  the  metabolism  of  the  ^ 
organ  it  supplies;  and  we  here  suggest  that,  if  this  view  were< 
applied  to  the  origin  and  course  of  cardiac  disease^  it  would^ 
result  in  a  gain  to  the  science  and  art  of  mediciivi. 


The  Accblbratos  (AuoMBirroR)  Nntyn  of  •osm  Hbabt. 

It  has  been  known  for  many  years  that  in  the  dog,  cat,  rab- 
bit, and- some  other  mammals,  there  were -nerves  proceeding 
from  certain  of  the  ganglia  of  the  sympathetic  chain  high  up, 
stimulatioa  of  which  led  to  an  aooelffiratioa  of  the  heart-beat. 
Very  recently  these  nerves  have  been  traced  in  a  number  of 
eold-blooded  animals,  and  the  whde  subject  placed  on  a  broader 
and  soundw  basis. 


THE  CntCULATION  OF  THB  BLOOD. 


971 


disorders  of/ 
angaish  or^ 
application  i 
>i&t  to  infla- 
life-processeBJ 

cold-blooded 
rates,  cofwisto 
proper  and 
system.  ' 

utritive  pro- 
ire.  This  has 
«  oonstntctive 
catabolic)  me- 
n  of  the  body 
>wiiig  anabolic 


any  more 
ry  of  the  body 
of  vhat  in  all 
9  implied  that 
kenupwMrd  in 
y  certain  down- 
s  too  rigid  and 

ce,  pathological 
int  may  believe^ 
le  body,  accord- 
teficial,  guiding^ 
tabolism  of  the « 
this  view  were< 
isease,  it  woold^ 
ne. 


There  are  variations  in  the  distribution  of  these  nerves  for 
different  groups  of  animals,  but  it  will  suflBoe  if  we  indicate 
their  course  in  a  ig^neral  way,  without  special  reference  to  the 
variations  for  each  animal  group :  1.  These  nerves  emerge  from 
the  spinal  cord  (upper  dorsal  region),  and  proceed  upward 
before  being  distributed  to  the  heart  2.  They  may  leave  for 
their  cardiac  destination  either  at  (a)  the  first  theraoic  (or  basal 
cardiac  ganglion,  as  it  might  be  named  in  this  case),  (6)  the  in- 
ferior cervical  ganglion,  (e)  the  annulus  of  VieussensyOr  (d)  the 
middle  cervical  ganglion. 


lO — 


lOonL 


AOMlMMtar  Oniter  tai  Itodnll*. 


Supgrior  Oar«iMd  GwnHoB. 


WddtoOw*lMd« 


InCarior  OBrriad  a«i«liaa. 


Bagtoaornntl 


UUwatanitor  X« 


BMrt. 


r  TKB  Hbabt. 

le  dog,  cat,  rab- 
rves  proceeding 
chain  high  up, 
the  heart-beat, 
n  a  number  of 
)ed  (ma  broader 


'JTll 


Their  course  haa  been  traoed  by  physiological  methods ;  thus 
it  has  been  found  that,  in  all  animals  Munined,  stimulation 
of  the  signal  cord  or  tiie  various  parts  mentioned  above,  or 
nofve  bmnches  from  them,  gave  rise  elttor  to  acceleration  of 


97S 


ANIMAL  PHT8I0L0OT. 


§'■■ 


the  cardiac  beat  or  augmentation  of  its  force,  or  to  both,  as  is 
commonly  the  case.  In  every  instance  the  work  of  the  heart 
is  increased,  so  that  they  may  be  called  more  appropriately 
augmerUor  nerves;  and  their  effect  may  be  more  evident  on 
one  part  of  the  heart,  as  regards  increase  of  the  force  of  the 
beat,  than  on  another. 

They  require  for  their  fullest  effect  a  rather  strong  and  con- 
tinuous stimulation  (interrupted  current),  and  the  augmenta^ 
tion  outlasts  the  stimulus  a  considerable  period.  The  samiB  law 
applies  to  them  as  to  the  vagus  nerve,  viz.,  that  the  result  is 
inversely  proportional  to  the  rhythm  of  the  heart  at  the  period 
of  stimulation;  a  slow-beating  heart  will  be  more  augmented 
proportionally  than  a  rapidly-pulsating  organ. 

It  is  noticeable  that  after  one  or  more  experiments  the  heart 
often  falls  into  an  irregular  or  weakened  action  quite  the  re- 
verse of  what  ensues  when  the  vagus  is  stimulated.  But  it  has 
als3  been  observed  that  certain  of  the  vagus  fibers  on  stimula- 
tion give  rise  to  a  like  result. 

Further,  it  is  found  that  the  electrical  condition  of  the  heart 
is  different,  according  as  the  inhibitory  or  other  fibers  of  the 
heart  are  stimulated.  The  latter  fact  seemed  to  poiat  strongly 
to  a  fundamental  difference  in  their  effect  on  cardiac  metabo- 
lism ;  hence  it  is  proposed  to  speak  of  the  vagus  as  a  vago- 
sympathetic nerve,  containing  inhibitory  fibers  proper  and 
sympathetic  or  motor  fibers  to  be  classed  with  the  nerves  that 
were  formerly  known  as  "accelerators,"  and  to  be  compared 
in  their  action  to  the  ordinary  motor  nerves  of  voluntary 
muscles. 

Indeed,  these  conceptions  will  probably  give  rise  to  a  broader 
view  of  the  whole  nervous  system,  especially  as  regards  the 
relations  of  the  nerves  themselves. 

Certainly  the  augmentor  nerves  to  which  we  are  now  refer- 
ring exhaust  the  heart,  lead  it  to  expend  its  nutritive  capital, 
and  leave  it  worse  than  before.  One  can  understand  the  ad- 
vantage in  the  heart  having  a  double  supply  of  nerve-fibers 
with  opposite  action;  and  it  is  worthy  of  special  note  in  this 
connection  that,  when  the  vagus  (vagOHsympathetic)  is  stimu- 
lated at  the  same  time  as  the  augmentors,  the  inhibitory  effect, 
preservative  of  nutritive  resources,  prevails. 

It  will  be  seen  that  the  heart  may  be  made  to  do  increased 
work  in  three  ways  i  Firstly,  the  relaxation  of  a  normal  inhibi- 
tory control  through  the  vagus  nerve  by  the  cardio-inhibitory 
center;  secondly,  through  Uie  sympathetic  (motor)  fibers  in 


ijlllKHW'j.i    ■! 


THB  GIBGULATION  OF  TH£  BLOOD. 


278 


both,  as  is 
I  the  heart 
propriately 
evident  on 
orce  of  the ' 

ig  and  oon- 
augmenta- 
Le  samiB  law 
le  result  is 
;  the  period 
augmented 

ts  the  heart 

uite  the  re- 

But  it  has 

on  stimula- 

of  the  heart 
ibers  of  the 
int  strongly 
iac  metabo- 
as  a  vago- 
proper  and 
nerves  that 
e  compared 
t  voluntary 

to  a  broader 
regards  the 

e  now  ref er- 
tive  capital, 
and  the  ad- 
nerye-fibers 
note  in  this 
ic)  is  stimu- 
t)itory  effect, 

lo  increased 
irmal  inhibi- 
io-inhibitory 
}r)  fibers  in 


the  vagus  itself ;  and,  finally,  through  fibers  with  similar  action 
in  the  sympathetic  system,  usually  so  called. 

The  share  taken  by  these  factors  is  certainly  variable  in  dif- 
ferent species  of  animals,  and  it  is  likely  that  this  is  true  of  the 
same  animals  on  different  occasions.  It  is  also  conceivable, 
and  indeed  probable,  that  they  act  together  at  times,  the  inhibi- 
tory  action  being  diminished  and  the  augmentor  influence  in- 
creased. 

Huuui  Phyiiokfy. — Of  the  three  cardiac  nerves — superior, 
middle,  and  inferior— the  strongest,  which  is  the  middle  one, 
passes  from  the  inferior  cervical  ganglion  to  the  middle,  from 
which  it  proceeds  to  the  heart,  and  the  inferior,  may  be  re- 
garded as  the  chief  augmentor  cardiac  nerves. 

That  man's  pneumogastric  contains  inhibitory  fibers  is  evi- 
dent from  the  experiment  of  Czermak,  who,  by  pressing  a  bony 
tumor  in  his  neck  against  his  vagus  nerve,  could  arrest  his 
heart  Another  individual  could  arrest  his  heart-beat  at  will, 
and  if  not  through  the  vagus,  how  ? 

We  are  probably  all  aware  of  alterations  in  the  rhythm  of , 
the  heart  from  emotiona  During  a  period  of  intense,  brief, 
sympathetic  anxiety,  as  in  w;atching  two  competitors  during  a' 
severe  struggle  for  supremacy,  a  change  in  the  rhythm  of  the 
heart,  amounting,  it  may  be,  to  momentary  arrest,  may  be 
observed. 

Enough  has  been  said,  we  trust,  to  show  that  the  nerves  of 
the  heart  can  no  longer  be  regarded  merely  as  the  reins  for^ 
bridling  the  cardiac  steed;  but  that  all  the  phenomena  of  accel- 
eration, slowing,  or  other  changes  of  rhythm,  are  only  the  out-' 
ward  evidences  of  profound  vital  changes  accompanied  by  cor 
responding  chemical  and  electrical  effects.  If  these  views  bCj 
correct,  nervous  influence  must  play  no  small  part  in  the  causa-^ 
tion  and  modification  of  disordered  conditions;  and  we  would 
extend  such  a  view  to  all  the  organs  of  the  body,  and  especially 
in  the  case  of  man.  The  heart's  rhythm  can,  however,  be^ 
modified  in  other  ways  than  we  have  as  yet  described. 

Though  an  isolated  heart,  fed  by  seruin  or  some  artificial 
nutritive  fluid,  may  beat  well  for  a  time,, it  is  liable  to  peri- 
odic interruptions,  which  are  probably  owing  to  its  imperfect 
nutrition. 

[llany  drugs  greatly  modify  the  heart-beat ;  but,  in  attempt- 
ing to  explain  how  the  result  is  accomplished,  the  difficulty  is 
in  unraveling  the  part  each  anatomical  element  plays  in  the 
total  result.    Does  the  drug  act  on  the  muscular  tissue,  the 

18 


jii.«i!ii4i<i)aw!wHii«m.u'WWBMM»«B«  'um » wwMWWwtlWIli 


274 


ANIMAL  PHTEUOLOOr. 


nerve  terminals,  or  the  ganglia;  or  does  it  afFect  the  heart 
through  the  central  nervous  system  ? 

Resort  to  comparative  physiology  is  important  in  such  cases, 
if  only  to  foster  caution  and  avoid  narrow  views. 


The  Heart  in  Relation  to  Blood-Prbssube. 

It  is  plain  that  all  the  other  conditions  throughout  the  cir- 
culatory system  remaining  the  same,  an  increase  in  either  the 
force  or  the  frequency  of  the  heart-beat  must  raise  the  blood-press- 
ure. But,  if  the  pressure  were  generally  raised  when  the  heart 
beats  rapidly,  it.would  fare  ill  with  the  aged,  the  eliEusticity  of 
their  arteries  being  usually  greatly  impaired.  As  a  matter  of 
fact  any  marked  rise  of  pressure  that  would  thus  occur  is  pre- 
vented as  a  rule,  and  in  different  ways,  as  will  be  seen ;  but,  so 
far  as  the  heart  is  concerned,  its  beat  is  usually  the  weaker  the 
more  rapid  it  is,  so  that  the  cardiac  rhythm  and  the  blood- 
pressure  are  in  inverse  proportion  to  each  other. 

By  what  method  is  the  heart's  action  tempered  to  the  condi- 
tions prevailing  at  the  time  in  the  other  parts  of  the  vascular 
system  ? 

(The  matter  is  complex.  It  is  possible  to  conceive  that  there 
is  a  local  nervous  apparatus  which  r^pilates  the  beat  of  the 
heart  according  to  the  intra-cardiac  pressure,  which  latter  again 
will  depend  on  conditions  outside  cd  the  heart  itself— the  arte- 
rial pressure,  ia  fact.  It  is  possible  to  understand  that,  apart 
from  any  nervous  elements  at  all,  the  cardiac  cells  regulate 
their  own  action  in  obedience  to  the  impressions  made  upon 
them. 

But,  inasmuch  as  the  heart,  is  not  regulated  perfectly  in  the 
ni«>mmal  according  to  the  blood-pressure,  when  the  vagi  nerves 
are  cut,  and  considering  the  dominance  of  the  central  nervous 
system,  it  does  not  seem  likely  that  it  should  resign  the  con- 
trol of  so  important  a  matter.  Experiment  bears  this  out. 
There  is  some  evidence  for  believing  that  not  only  may  the 
vagus  itself  act  as  an  afferent  sensory  nerve,  but  that  the  de- 
pressor nerve,  to  be  shortly  referred  to  more  particularly,  is 
also  such  a  sensory  nerve. 

However,  such  a  view  does  not  exclude  previously  men- 
tioned factors,  and  there  can  be  little  doubt  that  in  forms  below 
mammals  the  muscular  tissue  is  to  some  degree  self -regulative; 
and  it  is  not  likely  that  this  quality  is  wholly  lost  even  in  the 
highest  mammals. 


THE  GIROULATIOK  OP  THE  BLOOD. 


275 


it  the  heart 
a.  such  cases, 

BUBB. 

[lOut  the  cir- 
in  either  the 
iblood-presa- 
len  the  heart 
eliasticity  of 
^  a  matter  of 
Dccur  is  pre- 
seen ;  but,  so 
e  weaker  the 
d  the  blood- 
to  the  condi- 
the  vascular 

Ive  that  there 
)  beat  of  the 
blatter  again 
«lf— the  arte- 
id  that,  apart 
^lls  regulate 
18  made  upon 

»rf  ectly  in  the 
le  yag^  nerves 
intral  nervous 
esigh  the  con- 
9ars  this  out. 
only  may  the 
t  that  the  de- 
articularly,  is 

sviously  men- 
n  forms  below 
elf -regulative; 
st  even  in  the 


^•-^ 


The  effedt  of  vagu8  stimulation  on  the  blood-pressure  is 
always  very  marked,  as  would  be  supposed.  To  examine  an 
extreme  case,  suppose  the  heart  arrested  for  a  few  seconds,  the 
elastic  recoil  of  the  arteries  continues  to  maintain  for  a  time 
the  blood-pressure,  though  there  is,  of  course,  an  immediate 
and  pronounced  fall.  And  it  may  be  remarked,  by-the-way, 
that  in  cases  of  fainting,  when  the  heart  ceases  to  beat,  or  beats 
in  the  feeblest  man- 
ner, the  importance 
of  this  arterial  elas- 
ticity as  a  force, 
maintaining  the 
circulation  for  sev- 
eral seconds  at 
least,  is  of  great 
importance. 

As  seen  in  the 
tracing,  the  beats, 
when     the    heart  1 

commences  its  ac   '^aKl^gSS'rb&SSS^SSr^ 
tion  again,  tell  on       SL'^'^iTSi&rS'tff^SSlI^^ 

the    comparatively  ttgpyll>rcliM«etwrotth>cnw^qgriiliigbloo*|ii«MMT8 

slack  walls  of  the 

arteries,  distending  them  greatly,  and  this  may  be  made  evident 
by  the  sphygmograph  as  well  as  the  manometer ;  indeed,  may 
be  evident  to  Ihe  fii^;er,  the  jmlse  resembling  in  some  features 
that  following  excessive  loss  of  blood. 

If  the  heart  has  been  merely  slowed,  or  its  pulsation  weak- 
ened, the  effects  will  of  course  be  less  marked. 

Tks  (towBttty  of  llotd.-- The  blood-pressure  may  also  be 
augmented,  the  cardiac  frequency  remaining  tlM  same,  by 
the  quanti^  of  blood  ejected  from  the  ventricles,  which  again 
depends  on  the  quantity  entering  them,  a  factor  determined 
by  the  o(mdition  of  the  vessels,  and  to  this  we  shall  presently 
turn.  ' 

In  consequence  of  changes  in  different  parts  of  the  system 
by  way  of  compensation,  results  follow  in  an  animal  which 
might  not  have  been  anticipated. 

Thus,  bleeding,  unlesa  to  a  dangerous  extreme,  does  not 
lower  the  blood-pressure  except  temporarily.  It  is  estimated 
that  the  body  can  adapt  itself  to  a  loss  of  as  much  as  3  per 
cent  of  the  body-weigfai 

The  adaptation  is  probably  not  through  absorption  chiefly. 


iWh;***-*'.'*'^) 


IIIWilill.lWIltiMM 


276 


ANIMAL  PHTSIOIiOOT. 


k 
ft- 
I 


but  through  constriction  of  the  vessels  by  the  vaso-motor 
nerves. 

Again,  an  injection  of  fluid  into  the  blood  does  not  cause  an 
appreciable  rise  of  blood-pressure,  so  long  as  the  nervous  sys- 
tem is  intact ;  but,  if  by  section  of  the  spinal  cord  the  vaso- 
motor influences  are  cut  off,  then  a  rise  may  take  place  to  the 
extent  of  2  to  8  per  cent  of  the  body- weight,  the  extra  quan- 
tity of  fluid  seeming  to  be  accommodated  in  the  capillaries  and 
smaller  veins.  These  facts  are  highly  significant  in  illustrat- 
ing the  adaptive  power  of  the  circulatory  system  (protective  in 
its  nature),  and  are  of  practical  importance  in  the  treatment  of 
disease. 

^We  think  the  benefit  that  sometimes  follows  bleeding  has 
not  as  yet  received  an  adequate  explanation,  but  we  shall  not 
attempt  to  tackle  the  problem  now.  Changes  in  the  circulation 
depend  on  variations  in  the  size  of  the  blood-vessels. 

It  is  important  in  considering  this  subject  to  have  clear  no- 
tions of  the  structure  of  the  blood-vessels.  It  will  be  borne  in 
mind  that,  while  muscular  elements  are  perhaps  not  wholly 
lacking  in  any  of  the  arteries,  they  are  most  abundant  in  the 
smallest,  the  arterioles,  which  by  their  variations  in  size  are 
best  fitted  to  determine  the  quantity  of  blood  reaching  any 
organ.  It  is  well  known  that  nerves  derived  chiefly  from  the 
sympathetic  system  pass  to  blood-vessels,  though  their  exact 
mode  of  termination  is  obscure. 

We  may  now  examine  into  the  nature  of  certain  facts,  which 
may  be  stated  briefly  thus : 

1.  In  certain  vascular  areas  of  some  vertebrates,  as  in  the 
vessels  of  the  ear  of  the  rabbit  and  this  animal's  saphena 
artery,  rhythmical  variations  in  the  size  of  the  small  arteries 
may  be  observed ;  also  in  the  veins  of  the  bat's  wing  and  of  the 
fins  of  certai];|i  fishes  (e.  g.,  caudal  vein  of  the  eel),  as  well  as  in 
certain  arteries  of  some  groups  of  the  cold-blooded  animals. 

2.  Under  the  microscope  the  arterioles  of  various  parts  of 
the  frog,  including  those  of  the  muscles,  may  be  seen  to  vary 
apparently  spontaneously,  and  may  through  stimulation  be 
made  to  depart  widely  from  their  usual  size. 

3.  Section  of  a  large  number  of  nerves  is  followed  by  red- 
dening of  the  parts  to  which  they  are  distributed.  This  is  well 
seen  when  the  cervical  sympathetic  of  the  rabbit  is  divided ;  tiie 
ear  becomes  redder,  owing  to  obvious  dilatation  of  its  blood- 
vessels; and  warmer,  owing  to  the  increased  quantity  of  blood 
in  it,  etc.    It  has  also  been  noticed  in  cases  of  paralysis,  and 


THE  OIBCULATION  OF  THE  BLOOD. 


277 


vaBo-motor 

not  cause  an 
aervous  sys- 
■d  the  vaso- 
place  to  the 
extra  quan- 
pillaries  and 
in  illustrat- 
protective  in 
treatment  of 

bleeding  has 
we  shall  not 
Le  circulation 
lis. 

ive  clear  no- 
i  be  borne  in 
i  not  wholly 
ndant  in  the 
s  in  size  are 
reaching  any 
jfly  from  the 
li  their  exact 

n  facts,  which 

tes,  as  in  the 
[lal's  saphena 
small  arteries 
ng  and  of  the 
,  as  well  as  in 
d  animals, 
rious  parts  of 
seen  to  vary 
bimulation  be 

lowed  by  red- 
.  This  is  well 
B divided;  the 
L  of  its  blood- 
mtity  of  blood 
paralysis,  and 


especially  in  gunshot  and  other  wounds  involving  nerves,  that 
vaso-motor  effects  have  followed. 

4.  Section  of  certain  nerves,  as  the  nervi  erigentea  of  the 
penis,  is  not  followed  by  dilatation ;  but  these  nerves  and  the 
chorda  tympcmi  supplying  the  salivary  gland  are  examples  of 
so-called  vaao-dikUors,  inasmuch  as  their  stimulation  gives  rise 
to  enlargement  of  the  caliber  of  the  arterioles  in  their  area  of 
distribution. 

5.  On  the  other  hand,  such  a  nerve  as  the  cervical  sympa- 
thetic, as  may  be  readily  shown  in  the  rabbit,  when  its  periph- 
eral end  is  stimulated,  gives  rise  to  constriction,  and  hence  is 
termed  a  vaao-constrictor. 

6.  When,  however,  the  divided  sciatic  nerve  is  stimulated 
peripherally,  the  result  may  be  either  constriction  or  dilata- 
tion. 

7.  When  the  spinal  cord  of  an  animal  is  divided  across, 
there  is  vascular  dilatation  of  all  the  parts  below  the  section 
(loss  of  arterial  tone) ;  but  in  time  the  vessels  return  to  their 
usual  size  (restoration  of  arterial  tone). 

8.  On  destmction  of  a  certain  minute  portion  of  the  medulla 
oblongata,  there  is  a  general  loss  of  arterial  tone.  This  area 
(center)  extends  in  the  rabbit  from  a  short  distance  below  the 
corpora  quadrigemina  (1  to  2  mm.)  to  within  4  to  6  of  the 
calamus  scriptorius,  as  ascertained  by  the  effects  on  the  vessels 
of  cutting  away  the  medulla  in  thin  transverse  sections.  At 
the  spot  indicated  there  is  a  collection  of  large  multipolar 
nerve-cells  (antero-lateral  nucleus  of  Clarke). 

OoadwAaM. — 1.  There  are  vaao-m/oior  nerves  of  two  kind»— 
vcMO-etmsMdort  and  vaao-dUaHora — ^which  may  exist  in  nerve- 
trunks  either  alone  or  mingled. 

Examples  of  the  former  are  found  in  the  cervical  sympa- 
thetic, splanchnic,  etc.,  of  the  latter  in  the  chorda  tympani, 
nerves  of  the  muscles  and  nervi  erigentea  (from  the  first,  second, 
and  third  sacral  nerves),  while  the  sciatic  seems  to  contain 
both.  3.  Impulses  are- constantly  passing  frtfm  the  medullary 
vaso-motor  center  along  the  nerves  to  the  blood-vessels,  hence 
their  dilatation  after  section  of  the  nwves: 

The  nerves  are  traceable  to  the  spinal  cord,  and  in  some 
part  of  their  course  run,  as  a  rule,  in  the  sympathetic  system. 
3.  Impulses  pass  at  intervals  to  the  areas  of  distribution  of 
vaso-dilators  along  those  nerves,  the  effect  of  which  is  to  dilate 
the  vessels  through  their  influence,  as  in  other  cases,  on  the 
muscular  coat. 


'jmmmmmitm.mM'mmlmMmimL»JimiMi,immiiiiii.'i,yiitimmK<Amit'-,!awm^m 


278 


ANIMAL  PHYSIOLOGY. 


It  i8  stated  that  in  course  of  time  the  vessels  of  the  rabbit's 
ear  regain  their  tone,  notwithstanding  that  the  influence  of  the 


Yaao-motor  Centar  ia 
XeduUiu 


Spinal  Ooid 


Efferent  VMO-motor 
Nerve. 


OntlyincVawsatar^ 
Are*. 


AffanntltamfNm 
PeriplMry. 


pUcUytoadngto 


central  nervdus  system  has  been  cut  oflf  by  section  of  the  vaso- 

motor  nerves.  ,      .       ,_^  -^^ 

To  explain  this  result,  a  local  nervous  mechantsm  »«».  »»een 
assumed  to  exist,  though  not  demonstrated  either  M»fto°»«*»]ly 
or  physiologically.    I'^teresting  experiments  have  lately  Aown 
that  both  in  mammals  and  cold-blooded  animals  the  effe<J  on 
the  blood-vessels  varies  with  the  intensUy  and  character  of  ^e  ^ 
stimulus,  and  not  only  with  the  group  of  animals  tested  but 
even  with  the  same  individuals  at  different  periods  dunng  t^( 
experiment ;  and  we  take  the  opportunity  to  wnew  our  expws^, 
8i<m  of  opinion  with  this  fresh  evidence  that  the  laws  of  phyri.\ 
ology  cai  not  be  laid  down  in  the  rigid  way  that  has  prevaded/ 


tsmum  jKiVL^mumttKiMm 


♦.aBW'iKisM*-''*^^*'**"'***'^'****** 


the  rabbit's 
aence  of  the 


rUTCBtMMrwfhNB 
PMpherjr. 


arait  immilMi  firom 
MTMitoT^lmbi- 
MloonL  The cffer- 
for  Ow  win  oC  trim- 

Qof  the  vaso> 

lism  has  been 
r  anatomically 
e  lately  shown 
I  the  effect  on 
laracter  of  the  ^ 
als  tested,  bat 
ids  during  the(^ 
ew  our  expres-/ 
laws  of  physi-N 
i  has  prevailecL/ 


THE  CIBCULATION  OF  THB  BLOOD. 


879 


r. 


to  so  large  an  extent  np  to  the  present  time ;  but  that  our  widen- 
ing experience  shows  (what  ought  to  have  been  expected)  that 
the  greatest  allowance  mast  be  made  for  group  if  not  individ- 
ual  variations  ever>  where.  There  is  also  evidence  to  show  that 
th(*  mode  of  st  imulation  in  experimental  cases  causes  the  result 
to  Vary.  From  such  facts  as  are  stated  in  paragraph  seven,  it 
is  inferred  that  there  are  voso-motor  centers  in  the  spinal  cord 
which  are  usuaUy  subordinated  k)  the  main  center  in  the  me- 
dulla, but  which  in  the  absence  of  the  control  of  the  chief  cen- 
ter in  the  medulla  assume  an  independent  regulating  influence. 

A  local  vaso-motor  mechanism  does  not  seem  to  us  neces- 
sary to  explain  the  changes  which  the  blood-vessels  undergo, 
and  should  not  be  adopted  as  an  article  of  physiological  faith 
till  demonstrated  to  exist.  If  we  assume  that  the  independent 
contractility  oi  muscle-cells  is  retained  in  the  blood-vessels, 
and  that,  when  freed  from  the  influence  of  the  central  nervous 
system,  which  becomes  more  and  more  dominant  as  we  ascend 
the  animal  scale,  there  is  a  reversion  to  an  ancestral  condition, 
a  new  light  is  thrown  upon  the  facts.  Qtjs  a  case  of  J3ld  habits 
joining  sway  when  the  check-rein  of  nervous  iiofluence  is  re- 
move?;  and,  as  we  shall  ahow  from  time  to  time,  this  law  applies 
to everyoigan  of ^ebody.  Moreover, not  to  go  beyond  the 
varoJarsyiteSi-,  this  independent  rhythmic  activity  is  seen  in 
the  isolated  sections  of  the  pulsatile  veins  of  the  bat's  wing, 
devoid,  so  far  as  we  know,  of  nervous  cells.  Such  facts  lend 
some  color  to  the  view  that,  after  distention  of  the  vessels  by 
the  cardiac  systole,  the  return  to  their  previous  sise  is  aided  by 
rhythmical  contractions  of  the  muscle-cells. 

Let  us  now  consider  certain  other  well-known  experimental 
facts : 

1.  There  is  a  nerve  with  variable  origin,  course,  etc.,  in  dif- 
ferent mammals,  but  in  the  rabbit  given  off  from  eitiier  the 
vagus,  the  superior  laryngeal,  or  by  a  branch  from  each, 
which,  running  near  the  sympathetic  nerve  and  the  carotid 
artery,  reaches  the  heart,  to  which  it  is  distributed.  This  is 
known  as  the  depressor  nerve. 

a.  The  vagi  nerves  having  been  divided,  stimulation  of  the 
centand  eaxd  of  the  cut  depressor  nerve  is  followed  by  a  fall  in 
blood-pressure,  which  may  not  be  accompanied  by  any  altera- 
tion in  the  cardiac  rhythm. 

3.  This  effect  may  in  great  part  be  prevented  if  the  splanoh- 
nio  nerves  be  divided  previous  to  stimulation  of  the  depressor. 

4.  If  the  splanchnic  area  (region  of  the  main  abdominal 


'•n\ 


*^w>iMtfW«n«w<«»')lni*i 


gS;at&-'W:aaWA'JBa8i»Wlawmu.j<w!tyTU,^j»!ilBU'ii*Ji%uiHrji^i, 


iiiiiuM 


jgQ  ANIMAL  PHYSIOIXXJY. 

Viscera)  be  inspected  during  the  fall  in  blood-pressure,  it  may 
be  n>  ticed  that  there  is  vascular  fuUnees  under  these  ciroum- 

stanctib*  1      1.      IK       4.  * 

These  results  are  interpreted  as  being  due  to  afferent  im- 
pulses ascending  the  depressor,  acting  on  the  vaso-motor  center, 


■tfamW  (Fatter). 

and  interfering  with  (inhibiting)  the  outflow  of  efferent,  con- 
strictive, or  tonic  impulses,  which  start  from  the  vaso-motOT 
c^ter,  descend  the  c6rd,  and  find  their  way  to  the  organs  of 
the  region  in  question,  in  consequence  of  which  the  mus- 
cuhir  «)ats  of  the  arterioles  rehix,  more  blood  flows  to  th^8 
area  which  is  very  large,  and  the  general  bloci-pressure  is 

A«ain.  if  the  centna  end  of  one  of  the  main  neriree-e.  g., 
sciatS-be  stimulated,  a  marked  change  in  the  b^>od.pres8ure 
results^but  whether  in  the  direction  of  nse  or  fall  seems  to 
depend  upon  the  condition  of  the  central  nervous  system,  for, 
wiS  the  Mimal  under  the  influence  of  chloral,  there  is  a  faU ; 

if  under  urari,  a  rise.  .      ^      *  tx.^^ 

It  is  not  to  be  supposed  that  the  change  in  «fy  «  *Jf«« 

oases  is  confined  to  any  one  vascular  ^^^jT'Tf^^l^^lrTi 
it  is  this  or  that,  according  to  the  nerve  stimulated,  the  condi- 
tion  of  the  centers,  and  a  number  of  other  o"?^*^^^ 
Moreover,  it  is  important  to  bear  in  mind  that  ^*^  »f^  «f 
blood-pressure  in  one  region  there  may  be  a  <^™rt'»8  "^ 
in  another.  With  these  considerations  m  mind,  it  wUl  be  ajh 
parent  that  the  changes  in  the  yascuhur  system  during  the 


■it^awiiiifcMw*i'iii»^*iw««i 


THE  CIBCULATION  OF  THE  BLOOD. 


281 


iBure,  it  may 
lese  ciroum- 

a£Eerent  im- 
aotor  center, 


LAJUUU 

Btral  end  of  Uwd»- 
which  the  nooitfnc 
raa  throwa  into  IM 
^,  and  ontlMtii  th* 


efferent,  can- 
tie  va80>motor 
the  organs  <^ 
icli  the  mns- 

flowB  to  this 
od-preissore  is 

I  nerves— e.g., 
blood-pressure 
fall  seems  to 
09  system,  for, 
there  is  a  fall; 

d  aAy  of  these 
iably,  but  that 
bted,  the  oondi- 
ciroamstances. 
b  with  a  fall  of 
responding  rise 
1,  it  will  be  ap- 
nn  daring  the 


coarse  of  a  single  hoar  are  of  the  most  complex  and  variable 
character. 

Though  special  attention  has  been  drawn  to  such  rhyth- 
mical variations  as  may  be  witnessed  in  the  rabbit's  ear,  bat's 
wing,  etc.,  there  can  be  little  doubt  that  changes  as  markedj 
though  posisibly  less  distinctly  rhjrthmical,  are  constantly  tak^ 
ing  place  in  the  vertebrate  body,  and  especially  in  that  of  man,<, 
with  his  complex  emotional  nature  and  the  many  vicissitudes; 
/of  modeni  ci^^^uedHBIe.    The  frequent  changes  in  color  in  the 
faces  <7^Dertam  people  are  in  this  connection  suggestive,  though 
we  hope  we  have  made  it  clear  that  these  vascular  modifica- 
tions are  dependent  chiefly  on  centripetal  influences  from  every 
quarter,  though  actually  brought  about,  by  centrifugal  im- 
pulses. Whether  there  is  a  rhythm  obscured  by  minor  rh3rthms, 
owmg  to  an  independent  or  automatic  action  of  the  vaso-motor 
center,  though  not  improbable,  must  be  regarded  as  undeter- 
mined as  yet. 

The  question  of  the  distribution  of  vaso-motor  nerves  to 
veins  is  also  one  to  which  a  definite  answer  can  not  be  given. 

Thk  CapillabixsJ  7 

The  cells  of  which  the  capillaries  are  composed  have  a  con- 
tractility of  their  own,  and  hence  the  caliber  of  the  capillaries 
is  not  determined  merely  by  the  arterial  pressure  or  any  similar 
mechanical  effect. 

Certain  abnormal  conditions,  induced  in  these  vessels  by 
the  application  of  irritants,  cause  changes  in  the  blood-flow, 
which  can  not  be  explained  apart  from  the  vitality  of  the  ves- 
sels themselves. 

Watched  through  the  microscope  under  such  circumstances, 
the  blood-corpuscles  no  longer  pursue  their  usual  course  in  the 
mid-stream,  but  seem  to  be  generally  distributed  and  to  hug  the 
walls,  one  resalt  of  which  is  a  slowing  of  the  stream,  wholly 
independent  of  events  taking  place  in  other  Jressels.  It  is  thus 
seen  that  in  this  condition  {ataait)  the  capillaries  have  an  in- 
dependent influence  essentially  vital  We  say  independent,  for 
it  is  stiU  an  open  question  whether  nerves  are  distributed  to 
capillaries  or  not.  That  inflammation,  in  which  also  the  walls 
undergo  such  serious  changes  that  white  and  even  red  blood- 
cells  may  pass  through  them  (diapedesia),  is  not  uninfluenced 
by  the  nervous  system,  possibly  induced  through  it  in  certain 
cases,  if  not  all,  seems  more  than  probable.  --^ 


tm.'i^c:t^.i'»m'm»f»*TmtMm»MM 


I 


m»nmmmimm0im 


■MttMaWMtHUMi 


288 


ANIMAL  PHTSIOLOOT. 


But  when  we  consider  the  lymphatic  system  new  light  will, 
it  is  hoped,  be  thrown  upon  the  subject  of  the  nature  and  the 
influences  which  modify  the  capillaries.  One  thing  will  be 
clear  from  what  has  been  said,  that  even  normally  the  capil- 
laries must  exert  an  influence  of  the  nature  of  a  resistance, 
owing  to  their  {Mculiar  vital  properties;  and,  as  we  have 
already  intimated,  such  considerations  should  not  be  excluded 
from  any  conclusions  we  may  draw  in  regard  to  tubes  that  are 
made  up  of  living  cells,  whether  arteries,  veins,  or  capillaries, 
though  manifestly  the  applicability  to  capillaries  with  their 
less  modified  or  more  primitive  structure  is  stronger. 

It  has  now  become  clear  that  the  circulation  may  be  modi- 
fied either  centrally  or  peripherally ;  that  a  change  is  never 
purely  local, but  is  correlated  with  other  changes;  that  the 
whole  is,  in  the  higher  animals,  directly  under  the  dominion 
of  the  central  nervous  system;  and  that  it  is  through  this 
part  chiefly  that  harmony  in  the  vascular  as  in  other  sys- 
tems and  with  other  systems  is  established.  To  have  ade- 
quately grasped  this  conception  is  worth  more  than  a  knowl- 
edge of  all  the  details. 


Special  Coksiokkationb. 

BXlwlogtoaL— Changes  may  take  place  either  in  the  sab- 
stancd  of  the  cardiac  muscles,  in  the  vidves,  or  in  the  blood-ves- 
sels, of  a  nature  unfavorable  to  the  welfare  of  the  body.  Some 
of  these  have  been  incidentally  referred  to  already. 

Hypertrophy,  or  an  increase  in  the  tissue  of  tiie  heart,  is 
generally  dependent  on  increased  resistance,  either  within  or 
without  the  heart,  in  the  region  of  the  arterioles  or  capillaries. 
Imperf eotipns  of  the  aortic  valves  may  permit  of  regurgitation 
of  blood,  entaUing  an  extra  effort  if  it  is  to  be  expelled  in  addi- 
tion to  the  usual  quantity,  which  again  leads  to  hjrpertrophy ; 
but  this  is  often  succeeded  by  dilatation  of  the  chambers  of  tiie 
heart  one  after  the  other,  and  a  host  of  evils  growing  out  of 
this,  largely  dependent  on  imperfect  venous  circulation,  and 
increased  venous  pressure.  And  it  may  be  here  noticed  that^ 
«rterial  and  venous  pressures  »r%  as  a  general  rule,  in  inverse) 
proportion  to  each  other. 

If  the  quantity  of  blood  in  the  ventricle,  in  consequence 
of  regurgitation,  idiould  prove  to  be  greater  than  it  can  lift 
(eject),  the  heart  ceases  to  bdat  in  diastole;  hence  some  of  the] 
sudden  deaths  from  disease  of  the  aortic  valves. 


lltMMMUMi'MMMkillWMUMM 


f  light  will, 
ore  and  the 
ing  will  be 
y  the  capil- 
resistaace, 
18  we  have 
be  excluded 
bes  that  are 
capillaries, 
with  their 

BT. 

lay  be  modi- 
ige  is  never 
es;  that  the 
le  dominion 
ihroogh  this 
I  other  sys- 
o  have  ade- 
lan  a  knowl- 


in  the  8ab> 
he  blood-ves- 
body.  Some 
^ 

the  heart,  is 
ler  within  or 
>r  capillaries, 
regurgitation 
elled  in  addi- 
ijjrpertrophy ; 
unbers  of  l^e 
owing  oat  of 
mlation,  and 
noticed  that^ 
lie,  in  invwse; 

consequence 
n  it  can  lift 
e  some  of  th^ 


THE  CIBCULATION  OF  THE  BLOOD. 


888 


As  a  result  of  fatty,  or  other  forms  of  degeneration,  the 
heart  may  suddenly  rupture  under  strains. 

Actual  experiment  on  the  arteries  of  animals  recently  dead, 
including  men,  shows  that  the  elasticity  of  the  arteries  of  even 
adult  mammals  is  as  perfect  aa  tliat  of  the  vessels  of  the  child, 
so  that  man  ranks  lower  thaa  other  animals  in  this  respeci 

After  middle  life  the  loss  of  arterial  elasticity  is  consider- 
able and  progressive.  The  artariea  may  undergo  a  degenera- 
tion from  fatty  changes  or  deposit  of  lime ;  such  vessels  are,  of 
oomrse^  liable  to  mpfcure ;  hence  one  of  the  frequent  modes  of 
death  amoig  old  persons  is  from  paralysis  traceable  to  rupture 
of  vessels  in  the  IvailC^ 

These  and  oth«r  changes  also  cause  the  heart  more  work, 
and  may  lead  to  hypertrophy.  Bven  in  young  persons  the 
stn^  of  a  prokniged  athletic  career  may  entail  hypertn^hy 
or  some  other  form  of  haart'diseasflC^ 

We  mention  sneh  facts  as  these  to  show  the  more  clearly 
how  important  is  balance  kbA  the  power  of  ready  adaptati<m 
in  aiU  parts  of  the  dwalation  to  the  naintenaooe  of  a  healthy 
co^ndition  of  body. 

The  heart  is  itself  nourished  through  the  coronary  arteries ; 
so  that  morbid  alterations  in  these  vessels  cause,  if  not  sudden 
and  painful  death,  at  least  nutritive  changes  in  the  heart-sub- 
stance, which  may  lead  to  a  dramatic  end  or  to  a  slow  impair- 
ment of  cardiac  power,  etc. 

Termul  Obssmitiaa.— The  circulation  is  one  of  those  depart- 
ments«f  i^^siology  in  wUdk  the  etodmit  may  v«rify  much  upon 
his  owtt^iwfsuM.  Tlia  earffiae  impidse^  tiie  heartfs  sounds  (with  a 
double  «teihoeBop<^,  the  pnlae—its  naturs  and  ehanges  with  cir- 
cnmstaneeiy  the  venous  dronlattoo,  and-many  other  subjects, 
are  aU  easy  <oi  obaervation,  and  after  a  little  -  i»«rtioe  without 
liabiltty  of  causing  those  abnntations  due  to  the  attentirai  being 
drawn  to  one's  self. 

The  obeervations  need  not»  of  eonrae^  be  confined  tathe  stu- 
dent'ftown  penoil ;  it  1%  hxm^'mtt  very  important  that  the  nor- 
mal shoidd  belouMm  befem  the  obeervw  is  introduced  to  cases 
of  disaip&  Fnq«eat  compark»n  <if  the  nataral  and  the  dis- 
eased omidilioa  renders  plgfaiology,  pathology,  and  clinical 
medii^aa  mmdi,  good  service.  We4«iiin  srge  upon  the  student 
to  try  to  fofiB  inereaeingly  vi^  aibd  correct  nrantal  pictures 
of  the  oiroulationtmder  its  raangr elmiges. 

Oampaiittfe.— An  interesting  amuigement  of  blood-vesseb, 
known  as  a  nU  mtnoMfo,  oocurs  in  every  main  group  of  verte- 


SaWtWfSWWnwmn 


"^WWW'ill.illailWl 


I,     .  |.  .-■.--  I  iiiiiuirnirni 1— — "■■ 


284 


ANIMAL  PHTSIOLOOT. 


brates.  An  artery  breaks  up  into  a  great  number  of  vessels  of 
nearly  the  same  size,  which  terminate,  abruptly  and  without 
capillaries,  in  another  arterial  trunk. 


eSSSL 

They  are  found  in  a  variety  of  situations,  as  on  fee  carotid 
and  vertebrate  arteries  of  animals  that  naturally  feed  from  the 

ground  for  long  periods  together,  as  the  ruminants;  in  the 


m.m.-Mkmtt± 


((tolli>IIMi»BlliiMi<Wl»l»''«li»Mill 


HMMMMtH 


MJftiitiniiinni'iimwi 


mmm 


THB  CIBOULATION  OF  THB  BLOOD. 


28S 


sloth,  that  hangs  from  trees ;  in  the  legs  of  swans,  geese,  etc. ;  in 

the  horse's  foot,  in  which  the  arteries  break  np  into  many  small 

divisions.   C^t   has  been 

suggested  that   these  ar<     .^ 

rangements  permit  of  a 

supply  of  arterial  blood 

being  maintained  without 

congestion  of  the  parts. 

Very  marked   tortuosity 

of  vessels,  as  in  the  seal, 

the  carotid  of  which  is 

said  to  be  forty  times  as 

long  as  the  space  it  trav> 

erses,  in  all  probability 

serves  the  same  purpose. 

Ivotaittoa.  —  The  com- 
parative sketch  we  have 
given  of  the  vascular  sjrs- 
tem  will  doubtless  sug- 
gest a  gradual  evolution. 
We  observe  throughout  a. 
dependence  and  resem- 
blance which  we  think 
can  not  be  otherwise  ex- 
plained.   The  similarity 

of  the  foetal  circulation  in  the  mammal  to  the  permanent  circu- 
lation of  lower  groups  has  much  meaning.  Even  in  the  high- 
est form  of  heart  the  original  pulsatile  tube  is  not  lost  The 
great  veins  stiU  contract  in  the  mammal ;  the  sinus  venosus  is 
probably  the  result  of  Mending  and  expansion.  The  later 
differentiations  of  the  parts  of  Che  heart  are^learly  related  to 
the  adaptation  to  alteied  surroundings.  Such  is  seen  in  the 
f CBtal  heart  and  oiroulation,  and  has  probably  been  the  deter^ 
mining  cause  of  the  forms  which  the  circulatory  orgahs  have 
assumed. 

It  is  a  fact  that  the  part  of  the  heart  that  survives  the  long- 
est o&der  adverse  conditions  is  that  which  bears  the  stamp  of 
gntatest  ancestral  antiquity.  It  (the  sinus  vmosus)  may  not 
be  less  under  nervous  control,  but  it  certainly  is  least  depend- 
ent on  the  nervous  qrttem,  and  has  the  greatest  automaticity. 

It  is  surely  fortunate  for  man  that  this  i>art  of  the  reptilian 
heart  is  represented  in  his  own.  In  oases  of  fainting,  partial 
drowning,  or  other  instances  of  impending  death,  this  part,  with 


riM.  SO'.-VdHaf  UwftMto(ttalMn»(«flw 


386 


ANIMAL  PHYSIOLOGY. 


the  auricles  it  may  be,  continues  to  beat  when  the  ventricles 
have  ceased ;  and  we  have  learned  that  so  long  as  these  parts 
are  functionally  active  there  is  a  greater  probability  that  the 
quiescent  regions  may  recommence.  Activity  begets  activity, 
in  cardiac  muscle-cells  at  least.  How  are  these  facts  to  be 
explained  apart  from  evolution  P 

The  law  of  rfc|j^fcm  in  organic  nature  finds  some  of  its  most 
evident  exemplifications  in  the  circulation.  Most  of  the 
rhythms  are  compound,  one  being  blended  with  or  superim- 
posed on  another.  Even  the  apparent  irregularities  of  the  nor- 
mal heart  are  rhythmical,  such  as  the  very  marked  slowing 
and  other  changes  accompanying  expiration,  especially  in  some 

animals. 

We  trust  we  have  made  it  evident  that  the  greatest  allow- 
ance must  be  made  for  the  animal  group,  and  some  even  for 
the  individual,  in  estimating  any  one  of  the  factors  of  the  cir- 
culation. We  know  a  good  deal  at  present  of  cardiac  physiol- 
ogy, but  we  do  not  know  a  physiology  of  "the  heart"  in  the 
sense  in  which  we  understand  that  term  to  have  been  used  till 
recently— i.  e.,  we  are  not  in  a  position  to  state  the  laws  that-/  , 
apply  to  all  forms  of  heart. 

taantry  of  th*  Vkyridogj  of  th*  OixmOfftimi.— In  the  mammal 
the  circulatory  apparatus  forms  a  closed  system  consisting  of  a 
central  pump  or  heart,  arteries,  capillaries,  and  veins.  All  the 
parts  of  the  vascular  system  are  elastic,  but  this  property  is 
most  developed  in  the  arteries. 

Since  the  tissue-lymph  is  prepared  from  the  blood  in  the 
capillaries,  it  may  be  said  that  the  whole  circulatory  system 
exists  for  these  vessels. 

As  a  result  of  the  action  of  an  intermittent  pump  on  elastic 
vessels  against  peripheral  reristance,  in  consequence  of  which 
the  artmes  fire  always  kept  more  than  full  (distended),  the 
flow  through  the  capillaries  and  veins  is  constant-ra  very  great 
advantage,  enabling  the  capillaries  to  accomplish  their  work  <rf 
feeding  the  ever-hungry  tissues.  While  physical  forces  play  a 
very  prominent  part  in  the  circulation  of  the  blood;  vital  ones 
must  not  be  ignored.  They  lie  at  the  foundation  of  Uie  whole, 
here  as  elsewhere,  and  must  be  taken  into  the  account  in  every 
explanation. 

As  a  consequence  of  the  anatomical,  phydoal,  and  vital  char- 
acters of  the  circulatory  system,  it  follows  that  the  velocity  of 
I  the  blood  is  greatest  in  the  irteries,  least  in  the  capillaries,  and 
intermediate  in  the  veins. 


ithc 

(tat 


mUH 


mmmmm" 


-smms^im- 


THB  CUtCULATION  OF  THB  BLOOD. 


287 


he  ventricles 
these  parts 
lity  that  the 
sets  activity, 
facts  to  be 

of  its  most 
kCost   of   the 

or  superim- 
es  of  the  nor- 
rked  slowing 
Bially  in  some 

reatest  allow* 
ome  even  for 
rs  of  the  cir- 
■diac  physiol- 
leart"  in  the 
been  used  till 
the  laws  that«/ , 

1  the  mammal 
sonsisting  of  a 
eins.  All  the 
is  property  is 

»  blood  in  the 
ilatory  system 

imp  on  elastic 
ence  of  which 
listended),  the 
Hra  very  great 
i  iheir  work  of 
1  forces  play  a 
ood;  vital  ones 
t  of  the  whole, 
Qount  in  every 

and  vital  char- 
ihe  velocity  of 
japillariee,  and 


The  veins  with  their  valves,  their  superficial  position  and 
thinner  walls,  make  up  a  set  of  conditions  favoring  the  onflow 
of  the  blood,  especially  under  muscular  exercise. 

In  the  mammal  the  circulatory  system,  by  reason  of  its  con- 
nections with  the  digestive,  respiratory,  and  lymphatic  systems, 
and  in  a  lesser  d^pree  with  all  parts  of  the  body,  especially  the 
glandular  organs,  maintains  at  once  the  usefulness  and  the  fit- 
ness of  the  blood. 

The  arterioles,  by  virtue  of  their  highly  developed  muscular 
coat,  are  enabled  to  regulate  the  blood-supply  to  every  part,  in 
obedience  to  the  nervous  system. 

The  blood  exercises  a  certain  pressure  on  the  walls  of  all 
parts  of  tlie  vascular  system,  whidi  is  greatest  in  the  heart  it- 
self, high  in  the  arteries,  lower  in  the  capillaries,  and  lowest  in 
the  veins,  in  the  largest  of  which  it  may  be  lees  than  the  atmos- 
pheric pressure,  or  negative.  The  heart  in  the  mammal  consists 
of  four  perfectly  separated  chambers,  each  upper  and  each 
lower  pair  working  synchronously,  intermixture  of  arterial 
and  venous  Uood  being  prevented  by  septa  and  interference  in 
working  by  valves.  The  heart  is  a  force-pump  chiefly,  but,  to 
some  extent,  a  suction-p^mp  also,  though  its  power  as  such 
purely  from  its  own  action  and  independent  of  the  respiratory 
movements  of  the  chest  is  slight  under  ordinary  circumstances. 
In  consequence  of  the  lesser  resistance  in  the  pulmonary  divis- 
ion of  the  circulation,  the  blood-pressure  within  the  heart  is 
much  less  in  the  right  than  in  the  left  ventricle — a  fact  in  har- 
mony with  and  causative  of  the  greater  thickness  of  the  walls 
of  the  latter ;  for  in  the  foetus,  in  which  the  conditions  are  dif- 
ferent, this  distinction  does  not  hold. 

The  ventricles  usually  completely  empty  themselves  of 
blood  and  maintain  their  systolic  contracti<m  even  after  this 
has  been  effected.  The  contraction  of  the  heart,  which  really 
begins  in  the  great  veins  near  their  junction  with  the  auricles 
(that  do  not  fully  empty  themselves),  is  at  once  followed  up  by 
the  auricular  and  ventricular  contraction,'tiie  whole  constitu- 
ting one  long  peristaltic  wave.  Then  follows  the  cardiac  pause, 
which  is  of  longer  duration  than  the  entire  systole. 

When  the  heart  contracts  it  hardens,  owing  to  closing  on  a 
non-compressible  fluid  dammed  back  within  its  walls  by  resist- 
ance a  fronte.  At  the  same  time  the  hand  placed  on  the  chest- 
walls  over  the  heart  is  sensible  of  the  cardiac  impulse,  owing 
to  what  has  just  been  mentioned.  The  systole  of  the  chambers 
of  the  heart  gives  rise  to  a  first  and  a  second  sound,  so  called, 


J 


ANIMAL  PHTSIOLOGT. 


caused  by  several  events  combined,  in  which,  however,  the  ten- 
sion of  the  valves  must  take  a  prominent  share.  The  work  of 
the  heart  is  dependent  on  the  quantity  of  blood  it  ejects  and 
the  pressure  against  which  it  acts.  The  pulse  is  an  elevation 
of  the  arterial  wall,  occurring  with  each  heart-beat,  in  conse- 
quence of  the  passage  of  a  wave  over  the  general  blood-stream. 
There  is  a  distention  of  the  entire  arterial  system  in  every  di- 
rection. The  pulse  travels  with  extreme  velocity  as  compared 
with  the  blood-current.  The  heart-beat  varies  in  force,  fre- 
quency, duration,  etc.,  and  with  age,  sex,  posture,  and  numer- 
ous otiier  circumstances. 

The  whole  of  the  circulatory  system  is  regulated  by  the  cen- 
tral nervous  system  through  nerves.  There  is  in  the  medulla 
oblongata  a  small  collection  of  nerve-cells  making  up  the 
cardio-inhibitory  center.  This  center,  with  varying  degrees  of 
constancy,  depending  on  the  group  of  animals  and  the  needs 
of  the  organism,  sends  forth  impulses  (which  modify  the  beat 
of  the  heart  in  force  and  frequency)  through  the  vagi  nerves. 
There  are  nerves  of  the  sympathetic  sjrstem  with  a  center  in 
the  cervical  spinal  cord,  and  possibly  another  in  the  medulla, 
which  are  capable  of  originating  either  an  acceleration  of  the 
heart-rhythm  or  an  increase  of  the  force  of  the  beat,  or  both 
together,  known  as  accelerators  or  augmentors.  In  the  verte- 
brates thus  far  examined  the  vagus  is  in  reality  a  vago-sympa- 
thotic  nerve,  containing  inhibitory  fibers  proper,  and  symp»> 
thetic,  accelerator,  or  motor  fibers. 

The  inhibitory  fibers  can  arrest,  slow,  or  weaken  the  cardiac 
b^at;  the  sympathetic  accelerate  it  or  augment  its  force. 
When  botii  are  stimulated  together,  the  inhibitory  prevail. 

These  nerves,  as  also  the  accelerators,  exercise  a  profound 
influencci  upon  the  nutrition  of  the  heart,  and  effect  its  electri- 
cal condition  when  stimulated,  and  we  may  believe  when  influ- 
enced by  their  own  centers. 

The  inhibitory  fibers  tend  to  preserve  and  restore  cardiac 
energy;  the  sympathetic,  whether  in  the  vagus  or  as  the  aug- 
mentors, the  reverse.  The  vagus  nerve  (and  probably  the  de- 
pressor) acts  as  an  afferent,  cardiac  sensory  nerve  reporting  on 
the  intra -cardiac  pressure,  etc.,  and  so  enabling  the  vaso- 
motor and  cardio-inhibitory  centers,  which  are,  it  would  seem, 
capable  of  related  and  harmonious  action  to  act  for  the  general 
good. 

The  arterioles  must  be  conceived  as  undergoing  very  fre- 
quent changes  of  caliber.    They  are  governed  by  the  vaso- 


-.-»-/■,  ■■.,  «.Jii''-.'e''^»'»^''K^iMaw«.-V«*-*"": 


■it;^irt»ji9iri.7'«.«»''^ 


THE  CIRCULATION  OF  THB  BLOOD. 


989 


Bver,  the  ten- 
rhe  work  of 
it  ejects  and 
an  elevation 
aat,  in  conse- 
dood-Btreom. 

in  every  di- 
as  compared 
in  force,  fre- 

and  numer- 

3d  by  the  cen- 
1  the  medulla 
kking  up  the 
ing  degrees  of 
md  the  needs 
xlif  y  the  beat 
Bvagi  nerves, 
bh  a  center  in 

the  medulla, 

eration  of  the 

beat,  or  both 

In  ttie  verte- 
»  vagoHBjrmpa- 
r,  and  sympa* 

:en  the  cardiac 
ent  its  force. 
ry  prevail. 
Be  a  profound 
(ect  its  eleotri- 
ve  when  influ- 

•eetore  cardiac 
or  as  the  aug- 
obablythe  de- 
e  reporting  on 
ling  the  vaso- 
It  would  seem, 
for  the  general 

©ing  very  fre- 
.  by  the  vaso- 


motor center,  situated  in  the  medulla,  and  possibly  certain  sub- 
ordinate centers  in  the  spinal  cord,  througli  voso-motor  nerves. 
These  are  (a)  vaso-constrictors,  which  'untain  a  constant  but 
variable  degree  of  contraction  of  the  mu-ole-cells  of  the  vessels; 
(b)  vaso-dilators,  which  are  not  in  constant  functional  activity ; 
and  (c)  mixed  nerves,  with  both  kinds.  An  inherited  tendency; 
to  rhythmical  contraction  throughout  the  entire  vascular  sys- 
tem, including  the  vessels,  must  be  taken  into  account. 

The  depressor  nerve  acts  by  lessening  the  tonic  contraction 
of  (dilating)  the  vessels  of  the  splanchnic  area  especially. 

It  is  important  to  remember  that  all  the  changes  of  the 
vascular  system,  so  long  as  the  nervous  system  is  intact — i.  e., 
so  long  as  an  animal  is  normal — are  correlated ;  and  that  the 
action  of  such  nerves  as  the  depressor  is  to  be  taken  rather  as 
an  example  of  how  some  of  these  changes  are  brought  about, 
mere  chapters  in  an  incomplete  but  voluminous  history,  if  we 
could  but  write  it  all.  The  changes  in  blood-pressure,  by  the 
addition  or  rismoval  of  a  considerable  quantity  of  blood,  are 
slight,  owing  to  the  sort  of  adaptation  referred  to  above,  effected 
through  the  nervous  system.  Finally,  the  capillary  circiilation, 
when  studied  microscopically,  and  especially  in  disordered  cour 
ditions,  shows  clearly  that  the  vital  properties  of  these  vessels 
have  an  important  share  in  determining  the  character  of  the 
circulation  in  themselves  directly  and  elsewhere  indirectly. 

The  study  of  the  circulation  in  other  groujM  shows  that 
below  birds  the  arteriid  and'venous  blood  undergoes  mixture 
somewhere,  usually  in  the  heart,  but  that  in  all  the  Vertebrates 
the  best  blood  is  invariably  that  which  passes  to  the  head  and 
upper  regions  of  the  body.  The  deficiencies  in  the  heart,  owing 
to  the  imperfections  of  valves,  septa,  etc.,  are  in  part  counter- 
acted in  some  groups  ,by  pressure  relations,  the  blood  alwiays 
flowing  in  the  direction  of  least  resistance,  so  that  the  above- 
mentioned  result  is  achieved. 

Capillaries  are  wanting  in  most  of  the  invertebrates,  the 
blood  flowing  from  the  arteries  into  spaces  (sinuses)  in  the  tis- 
sues. It  is  to  be  noted  that  a  modified  blood  (lymph)  is  also 
found  in  the  interspaces  of  the  cells  of  organs.  Indeed,  the 
circulatory  system  of  lower  forms  is  in  many  respects  analogous 
to  the  lymphatic  system  of  higher  one& 
w 


I    Mill* 


990 


ANIMAL  PHTSIOLOGT. 


DIQBBnON  OF  FOOD. 


tA 


The  processes  of  digestion  may  be  considered  as  having 
for  their  end  the  preparation  of  food  for  entrance  into  the 
blood. 

This  is  in  part  attained  when  the  insohible  parts  have  been 
rendered  soluble.  At  this  stage  it  becomes  necessary  to  inquire 
as  to  what  constitutes /ood  or  a  food. 

Inasmuch  as  animals,  unlike  plants,  derive  none  of  their 
food  from  the  atmosphere,  it  is  manifest  that  what  they  take  in 
by  the  mouth  must  contain  every  chemical  element,  in  some 
form,  that  enters  into  the  composition  of  the  body. 

But  actual  experience  demonstrates  that  the  food  of  animals 
must,  if  we  except  certain  salts,  be  in  organized  form — i.  e.,  it 
must  approximate  to  the  condition  o^  the  tissues  of  the  body  in 
a  large  degree.  Plants,  in  fact,  are  necessary  to  animals  in 
working  up  the  elements  of  the  earth  and  air  into  form  suit- 
able for  them. 

Foodstuffs  are  divisible  into : 

I.  Organic. 

1.  Nitrogenous. 

(a.)  Albumina 

(5.)  Albuminoids  (as  gelatine). 
8.  Non-nitrogenous. 

(a.)  CarV^hydrates  (sugars,  starches). 
,    ib.)  Fatfa. 

II.  Inorganic, 

1.  Water. 

8.  Salt& 

Animals  may  derive  the  whole  of  their  food  from  the 
bodies  of  other  animals  (oomtvoro);  from  vegetable  matter 
exclusively  {herbivora) ;  or  from  a  mixture  of  the  animal  and 
vegetable,  as  in  the  case  of  the  pig^  bear,  and  man  himself 
{omnivora). 

(U  has  been  found  by  feeding  experiments,  carried  out  mostly 
on  oogs,  that  animals  die  when  they  lack  any  ore  of  the  con- 
stituents of  food,  though  they  live  longer  on  the  nitrogenous 
than  any  other  kind.  In  some  instances,  as  when  fed  on  gela- 
tine and  water,  or  sugar  and  water,  the  animals  died  almost  as 
soon  as  if  they  had  been  wholly  deprived  of  food.  But  it  has 
also  been  observed  that  some  animals  will  all  but  starve  rather 
than  eat  certain  kinds  of  food,  though  chemically  sufficient. 


Mrwa 


IMHMiiiHiniMf 


DIQBSnON  UP     OOD. 


Ml 


'od  as  having 
anoe  into  the 

rts  have  been 
sary  to  inquire 

none  of  their 
at  they  take  in 
ment,  in  some 

ood  of  animals 
I  f  orm— i,  e.,  it 
i  of  the  body  in 
to  animals  in 
into  form  suit- 


food  from  the 
Bgetable  matter 
the  animal  and 
id  man  himself 

brried  out  mostly 
or  a  of  the  oon- 
the  nitrog^enous 
hen  fed  on  gela- 
s  died  almost  as 
ood.  But  it  has 
mt  starve  rather 
ioally  sufficient. 


We  must  thus  reoognize  something  more  in  an  anin  Itan 
merely  the  mechanical  and  chemical  processes  which  o  ice  to 
aooomplish  digestion  in  the  laboratory.  A  food  must  e  not 
only  sufficient  from  the  chemical  and  physical  point  vipiw, 
but  be  capable  of  being  acted  on  by  the  digestive  juices,  and 
of  such  a  nature  as  to  suit  the  particular  animal  that  eats  it 

To  illustrate,  bones  may  be  masticated  and  readily  digested 
by  a  hyena,  but  not  by  an  ox  or  by  man,  though  they  meet  the 
conditions  of  a  food  in  containing  all  the  requisite  constituents. 
Further,  the  food  that  one  man  digests  readily  is  scarcely  digesti>'> 
ble  at  all  by  another ;  and  it  is  within  the  experience  of  every) 
one  that  a  frequent  change  of  diet  is  absolutely  necessary.    ^-^ 

Since  all  mammals,  for  a  considerable  period  of  their  exist- 
ence, feed  ujwn  milk  exclusively,  this  must  represent  a  perfect 
or  typical  food.  It  will  be  worth  while  to  examine  the  compo- 
sition of  milk.  The  various  substances  composing  it,  and  their 
relative  proportions  for  different  animals,  may  be  seen  from  the 
following  table,  which  is  based  on  a  total  of  1,000  parts : 


Hum. 

Oow. 

OoO. 

Water 

888^ 

887-OB 

868-88 

GHain 

Albamin. 

Butter. 

88-84 

80*60 

48-64 

1-88 

i      48-98 

}        5-78 

48-06 

40-87 

S-48 

88-60 

.  18-89 

48-57 

40D4 

6-88 

Milk-cucar 

bmTT:.:.  .:::. 

Total  Kdids..  

llQrn 

148-86 

186-48 

010-84 


90-18 
18-66 
67-08 


88-78 


The  fact  that  human  milk  is  poorer  in  proteids  and  fats 
especially  is  of  practical  importance,  for,  when  cow's  milk  is  sub- 
stituted in  the  feeding  of  infants,  it  should  be  diluted,  and  sugar 
and  cream  added  if  the  normal  proportions  of  mother's  milk 
are  to  be  retained. 

1.  The  proteids  of  milk  are  f 

(a.)  An  albumin  very  like  semm-«lbumki. 

(fi.)  Casein,  normally  in  suspension,  in  the  form  of  extremely 
minute  particles,  which  contributes  to  the  opacity  of  milk. 

It  can  be  removed  by  filtration  through  porcelain ;  and  pre- 
cipitated or  coagulated  by  acids  and  by  rennet,  an  extract  of 
the  mucous  membrane  of  the  calf's  stomach.  After  this  coagu- 
lation, whev,  a  fluid  more  or  less  clear,  separates,  which  con- 
tains the  salts  and  sugar  of  milk  and  most  of  the  water.  Much 
of  the  fat  is  entangled  with  the  casein. 


] 
I 


»niei«us>a,t«»Ki«i)Hi 


292 


ANIltAL  PHYSIOLOGY. 


Casein,  with  Bome  fht,  makes  up  the  greater  {^  i,rt  of  dh^efleV 

2.  F(Us. — Milk  is  an  emulsion — i.  e.,  contains  fat  euspdnded 
in  a  fine  state  of  division.  The  globules^  ^hioh  vary  greaitly  in 
size,  are  surrounded  by  an  envelope  of  proteid  matter.  This 
covering  ib  broken  up  by  churning,  allowing  the  fatty  globules 
to  run  together  and  form  butter. 

Butter  consists  chiefly  of  olein,  palmitin,  and  stearin,  but 
contains  in  smaller  quantity  a  variety  of  other  fats^  The  ran- 
cidity of  butter  is  due  to  the  presence  of  free  fatty  acids,  espe- 
cially butyric. 

The  fat  of  milk  uBually  rises  to  the  surface  as  cream  when 
milk  is  allowed  to  stand. 

3.  Milk-sugar,  which  is  converted  into  lactic  acid,  probably 
by  the  agency  of  some  form  of  micro^>rganism,  thus  furnish- 
ing acid  sufficient  to  cause  the  precipitation  or  coagiilation  6f 
the  casein. 

Mnk-mgw.       iMtioMid. 

C.H..O.=  «C.H.O.  V 

Milk,  when  fresh,  should  be  neutral  or  faintly  alkaline. 

4.  SoMs  (and  other  extractive^),  consistiiig  of  phosphateis  of 
calcium,  potassium,  and  magnei^ium,  potassium  chloride,  with 
traces  df  iron  and  other  substances.  j 

^  can  bf9  readily  understood  yfby  childrein  fed  on  milk  rarely 
suffer  froni  that  deficiency  of  ci^ium  salts  in  the  bones  leading 
to  rickets,  to  common' in  ill-fed  (^Idren.  It  thus  appears  that 
milk  contains  all  the  constituents  requisite  for  the  building  up 
of  the  healthy  mammalian  body;  and  experiments  prove  that 
these  exist  in  proper  proportions  and  in  a  readjly  digestible 
form.  The  author  has  found  that  a  large  number  bf  uiqiials, 
into  the  usual  food  of  which,  in  the  adult  form,  milk  does  npt 
enter,  like  most  of  our  wild. mammals,  as  well  ^JEf  mo^  l^rids, 
will  not  only  take  milk  but  soon  learn  to  like  ii,  and  thrive  Well 
upon  it.  Since  the  embryo  chick  lives  upon  the  egg,  it  utiis^t 
have  been  supposed  that  eggs  would  form  excenent  'fdod  for 
adult  animals,  and  bommon  experience  proves  this  t6  m  |he 
okse ;  while  chemical  analysis  shows  that  they,  like,  mil'ki.  bb9- 
tain  all  the  necessary  food  constituents.  Meat  (muscld,  with 
fat  chiefly)  is  also,  of  course^  a  valuable  food,  abbuiiditig'.ii^ 
proteids.  Cereals  contain  starch  in  large  proportion,  but  ailsd^^ 
mixture  of  proteids.  Chreen  vegettMes  contain  litile  actual  'nS;t-, 
tritive  material,  but  are  useful  in  furnishing  salts  'Imd  s^ial ', 
substances,  Iem  certain  compounds  of  siilphur  which,  in  SOjOQ^  litt- ' 
understood  way,  act  beneficially  on  the  metabolism  of'  the  fxMly'. 


irt  of  dhfee^i 
fat  suspended 
ary  greaitly  in 
matter.    This 
fatty  globules 

Ld  stearin,  but 
ata  Tberaia- 
;ty  acids,  espe- 

is  cream  when 

acid,  probably 
,  thus  f uraish- 
coagiilation  of 


J  alkaline, 
phosphateis  of 
chloride,  with 


.  on  milk  rartily 
9  bones  leading 
18  apx>ear8  that: 
the  building  up 
jnts  prore  that 
ftdily  digestible 
iber  tof  iuii?iials, 
,  MSk  does  npt 
^  mbikt  biijds, 
,  and  thrive  Well 
B  ?gg»  it.vriii^t 
celient  fbCKi  for 
I  this  t6  be  the 
likes"  milWc^^- 
it  (muscle,  with 
1,  abbuiidiAgii^ 
»rtion,biitaa86>' 
Utile  actual  rW- 
altsand  E^iia;! 
lich,  i^  9ojtt6  xll- 
iismoY'thetiody'. 


DIQBSTION  OF  FOOD. 


They  also  seem  to  stimulate  the  flow  of  healthy  dig^rtive  ^uids. 
Cfmdimenta  act  chiefly,  perhaps,  in  the  latter  way.  (Te»>  coffee, 
etc.,  contain  alkaloids,  which  it  is  likely  have  a  conservative 
effect  on  tissue  waste,  but  we  really  know  very  little  as  to  how 
it  is  that  they  prove  so  beneficial.  Though  they  are  recognized 
to  have  a  powerful  effect  on  the  nervous  system  as  stimulants, 
nevertheless  it  would  be  erroneous  to  suppose  that  their  action 
was  confined  to  this  alone. 


^aagmfig^^i^^t^i 


994 


ANMAL  PHTBIOLOGY. 


It  is  plain  that  if ,  in  the  digestive  tract  foods  are  changed 
in  aolubmty  and  actual  chemical  constitution,  this  must  have 


been  brought  ^bout  by  chemical  agencies.  That  food  is  broken 
^^t  X  very  commencement  of  the  alimentary  trwt  is  a 
Ztt  o?  Sirobservation;  and  that  there  Aould  be  a 
^^  movement  of  the  food  from  one  part  of  the  canal  to 


& 


fto.»l. 


huip;  a. 


!  «,« 


iX  •*.« 


Dvasmovi 


another,  where  a  different  fluid  is  seoreted,  would  be  expected. 
As  a  matter  of  fact,  mechanioal  and  chemical  forces  play  a 
large  part  in  the  actual  preparation  of  the  food  for  absorption. 
Behind  these  lie,  of  course,  the  vital  properties  of  the  glands, 
which  prepare  the  active  fluids  from  the  blood,  so  that  a  study 
of  digestion  naturally  divides  itself  into  the  consideration  of — 


Ito.  ■&— ilmtNoOM 
a. 


.mSS!StAS!^&£SSA^' 


1.  The  digestive  juices;  8.  The  secretory  processes;  and,  S.  The 
muscular  and  nervous  mechanism  by  which  the  food  is  carried 
from  one  part  of  the  digestive  tract  to  another,  and  the  waste 
matter  finally  expelled. 


rra.  M.-Uw|ttadliial  wtfMl  Motta  of  bo«]r «( iMOh,  JEMrMtfo  wyi«t«i«aW»»<'gJ!?'^Mg- 


lateyoisilsaL— The  alimentary  tract,  as  we  have  seen,  is 
formed  by  an  infolding  of  the  splanohnopleure,  and,  according 
as  the  growth  Is  moreor  loss  marked, does  thaoanal  become 


itmu 


9K 


HmUAh  PHYSIOLOGY. 


iio^aoas  ot  remain  «>mewhat  straight.  The  aUtnefltary  1*act 
Df  a  mammal  passes  through  stages  of  development  which  cor- 
respond with  the  permanent  form  of  other  groups  of  verte- 
brates, according  to  a  general  law  of  ev^ution.  Ihasmuch  as 
the  embryonic  gut  is  formed  of  mesoblast  and  hypoblast,  it  is 
easy  to  «flder«ti¥nd  why  the  developed  tract  should  so  mvana- 
bly  coi^sist  of  glandular  structures  and  muscular  tissue  dis- 
posed in  a  certain  regular  arrangement.    The  fact  that  all  the 


%| 


SB     ■■>■■     I        .         #- 

l^ainMtlMbrMntMita 

MO  0»  uBODiVEW* 

poiatoT 


organs  that  pour  digestive  juioe.  into  the  ^^i«»«'^i»'y  .*^*" 
oX~wths  t^m  it  serves  to  explain  why  the«»  should  remain 
r^siologioal  connection  with  an  anatomical  isolation.    The 

general  r^mblance  of  the  epithelium  t^^S^^^^*' «^^^„^ 
narts  widely  separated,  also  becomes  clear,  as  well  as  many 
5?^r  ^nS  ^r^n  nit  now  wf er  to  in  det«lV  to  <«e  who 
realizeTthe  significance  of  the  laws  of  d«went  (evolution). 
■■'  .  0«ipli«*<ft'-^Aii«8ba  ingerts  and  digests  apparently  by 
ev^ry  Si  bf  its  bodyr  though  exact  studieii  have  ihowii  thi^ 
if.  neit1i^«<J66pts  il«***tAin«  i^ithotit  oonsiderable  power  of 


!^!<imt^tm«mm'fMimm!.vftit^iiim<f»sm»«>«»»^ssmf 


ifflMSKiSWHWliWIW^WiwRW 


rnQsaraoH  A)V  food. 


SOI 


fnentary  1*act 
mt  whicli  cor- 
>up8  of  verte- 
Inasmuch  as 
ypoblast,  it  is 
lid  BO  invaria- 
lar  tissue  dis- 
ct  that  all  the 


I  ota«l(afler  BooMMii). 
aSuHL  taammAm 
Si  ainoe  OMtr  «>*»*■ 
ariyiMph,  Mia  rfgte  <rf 
«T  erode  or  mtfWm*- 
Hi  wraintkMUurjr  potat  or 


lentary  tract  are 
«  Bhionld  remain 
lisolatioii.  The 
aghout,  even  in 
IS  well  as  many 
(tall,  to  one  who 
(evolution). 
B  apparently  by 
have  ihown  that 
derable  power  of 


:di^iiuin»tioni;.  Hind  it  is  also  possible  that  some  sort  of  digest- 
ive fluid  may  be  secreted  from  the  part  of  the  body  with  which 
the  fodd-ptuticles  oome  in  contact.  It. has  been  shown,  too, 
that  there  are  4ifferences  in  the  digestive  capacity  of  closely 
allied  formsamdng  Infusorians. 

The  ciliated. Xufnsorians  have  a  permanent  mouth, which 
may  also  serve  as  an  anus;  or,  there  may  be  an  anus,  though 
xutaaUy  less  distinct  fiom  the  rc«t  of  the  body  than  the  mouth. 

Among  the  Coelenterates  mtra-ceUular  digestion  is  found. 
Certam  cells  of  the  endoderm  (as  in  Hydra)  take  up  food-parti- 


B).   Rata  tha  IMC  pnfeoMta 
•rauad  Um 


oles  Amceba-like,  digest  them,  and  thus  provide  material  for 
^e»  eelli'>ii#^NIeH  ^  themselves,  in  a  form  snitlMe  for  assimi- 
lation.   This  is  a  beginning'  of  that  cHifercnittatioti  of  function 


..di 


HMMifiMMHk 


MMMMaaMM 


S98 


ANIMAL  PHTBIOIiOOY. 


which  is  carried  so  far  among  the  higher  yertebratoa.  Bnl^  as 
recent  investigations  have  shown,  such  intra-oellalar  digestion 
exists  to  some  extent  in  the  alimentary  canal  of  the  highest 
members  of  the  vertebrate  group  (see  page  345). 

The  means  for  grasping  and  triturating  food  amoi^s:  in- 
vertebrates are  very  complicated  and  varied,  as  are  also  thow 
adapted  for  sucking  the  juices  of  prey.  Examples  to  hand  are 
to  be  found  in  the  crab,  crayfish,  spider,  grasshopper,  beetti^ 


■to.  ase, 


•.■tonwcli;  r.natnm;  a,tmmt  r.«,rMaliac:  k,lMM(;  l,hm(OaodiM  BalJiiiloliMn- 
bw);  m  to  •xtataal  laStun;  •mjuiii*  adm  ormMlli  nSSa  wMi  Mciotbodf ;  /, 
foot;  iijiD  iiiiiiliul. iiiiial.  mil imlilii  ■iihiiiiiiilii tiiiilh  ■igiimliil  iiiiiiiil tiiWil 


etc.,  on  the  one  hand,  and  the  butterfly,  house-fly,  leech,  eta, 
on  the  other. 

The  digestive  system  of  the  earth-worm  has  been  studied 
with  some  care.  It  illustrates  a  sort  of  extra-corporeal  diges- 
tion, in  that  it  secretes  a  fluid  from  the  mouth  which  seems  to 
act  both  chemically  and  mechanically  on  the  starch-graiiis 
of  the  leaves  on  which  it  feeds.  It  is  provided  with  an  organ 
in  which,  as  with  birds,  small  stones  are  found,'80  that  the 
imperfections  of  its  mouth  are  compensated  for  by  this  gissard 
which  triturates  the  food.  Its  caldferous  glands  supply  the 
alkaline  fluids  necessary  to  neutralise  the  humus  acids  of  de- 
caying leaves,  for  intestinal  digestion  only  proceeds  in  an  alka- 
line medium. 

The  gastric  mill  of  a  crab  (Fig.  Siia)  is  a  provision  of  ob- 
vious valuQ  in  so  voracious  a  oreatursw 


«^sai!?t-:>«A>i[«i«g!m!ami^v!»issm^miK^ 


DIOBBTION  OF  FOOIK 


S89 


Uea.  Bu%M 
liar  digestion 
I  the  highest 

d  amons  ™~ 
ire  alaothoM 
» to  hand  are 
io^ipear,  beetle^ 


orop; 
_.  ohun- 

bodr;/, 

MdiwudgnJM. 


>-fly,  leech,  etc., 

18  been  studied 
Borporeal  diges- 
which  seems  to 
te  starch-graips 
I  with  *n  organ 
md,'BO  that  the 
r  by  this  giszard 
Bkuds  supply  the 
bus  Boids  of  de- 
seeds in  an  alka- 

proTision  of  ob- 


(iefore  passing  on  to  higher  groups,  it  will  b*  well  to  bear 
in  mind  that  the  digestiw  organs  are  to  be  lagMidAdas  the  out- 
come both  of  he- 
redity and  adap-  .jtSTK 
tation  to  circum- 
stancea  We  find 
parts  of  the  in- 
toatine,  e.  g.,  re- 
tained  in  some 
animals  in  whose 
economy      thej 
seem    to    serve 
little  if  any  good 
purpose,  as  the 
vermiform     ap- 
pendix of  max 
Adaptation   has 
been  illustrated 
in    the  lifetime 
of  a  single  indi- 
vidual in  a  re- 
markable 
ner ;  thus,  a 
gull,by  being  fed 
on  grain,  has  had 
its  stomach,  nat- 
urally thin  and 
soft-waUed,  con- 
verted   into     a 
muscular      gia- 
sard. 

(^oe  diges- 
tion is  a  process 
in  which  the 
mechanical  and 
chemical  are 
both  involved, 
and  the  food  of 
mimals    difl«ps  t^v  .«> 

so  widely,  great  variety  in  the  aUmentair  tract,  b^  jw^ 
tomical  and  physiological,  must  be  expected.  y«»*«»JJ* '^J 
myvA  usually  be  eaftmi  in  much  larger  bulkto  ««^*^* 
needed  elemMits;  hMioe  ttie  great  tength  of  intestina  habitually 


^0itij^jauiSi3BSiSSSSm 


fpttp4,  ilk  )i9FWvqT«up  animals,  a^sodate^  often  with, a  capaciou» 
a|a4  oUml>9i^  ftQma<?l^  fi^nishiftg/aJUwrger  la^^^         in 


which  Nature  may  carry  on  her  processes.  To  illustrate,  the 
stomach  of  the  ruminants  consists  of  four  parts  {rumen,  reticu- 
Itm,  &n«cuivk»  tp8atUmwn)labomaaum^  The  food  wten  cropped 
is  imniedittteiy  swallowed  ;,i  so  th^t  the  pan^ich  iruanen)  w  a^ 
mere  Btorehtfttse  ih  which  it  is  sdf tenJed^  thoi»gh  but,  little 
changed  l<»t]^iiw^i»;«i»4itniroMldB««m  tha^  real  gastric  di- 


i^iioiB^io^  6p'^6bt>. 


,A 


m 


geBtion  is  almost  confined  to  the  last  division,  which  may  be 
compared  to  the  simple  stomach  of  the  Camivora  or  of  man; 
and,  before  the  food  reaches  this  region,  it  has  been  thoroughly 
masticated  and  mixed  with  saliva. 


.  «».-Stoni«oh,  pmoreM,  lam 
Bvw;  a.giOI-MaMM':  S>Mfct* 


•MtiaB  of 


I,  antwrior  aarface  of 
:  4,  pwArior  mrf aoe  of  atomaMi ;  S, 

yarSrin! '^j^Jfl^'^ n'''niMirw?nf  ^liiaiTiiUiffn'Trir-'^ •  IS,  dModeniiin;  IS,  upper  tx- 
SSonTn.  aS*^  flaxiMot  talon  ;l|  reotum ;  ll,  urlnanr  Madder. 


•te:  (after  Swer). 

»,=r    •  ...-.— «i»  .  -,-, Jmsmi  4,  pQaterfor_ 

lobiM  lS«em  of  Uv«r :  6,  ooeUao^;  MMramig7  <  ' 


The  reticulum  is  especially  adapted  for  holding  water,  which 
may  serve  a  good  purpose  in  moistening  and  thinning  the  con- 
tents of  the  stomach.  In  the  camels  and  llamas  a  portion  of 
the  stomach  is  made  up  of  pouches,  which  can  be  closed  with 
sphincter  muscles,  and  thus  shut  off  the  water-supply  in  sep- 
arate tanks,  as  it  were. 

The  stomach  of  the  horse  is  small,  though  the  intestine, 
especially  the  large  gut,  is  capacious. 

The  stomach  is  divisible  into  a  cardiac  region,  of  a  light 
cQlor  iiiternally,  aud  lined  with  epithelium,  like  tiuit  of  the 


/j 


\r "  iiiTi  \'ii' I iiw'ii ill '  1" ' ''    "  "'''^'•'^'^^ 


OlOBSTIOM  OF  POOD. 


ao8 


oawphagoB,  and  a  redder  pyloric  area,  in  which  the  greater 
p«rt  of  the  digestive  procesa  goes  on. 


Fie.  Ma-BtooMdi  of  dof  «Mv  CSiMmMi) 


i^iqrlonii. 


The  mouth  parts,  even  in  some  of  the  higher  vertebrates,  as 
the  Camivoroi  serve  a  prehensile  rather  than  a  digestive  pur- 
pose. This  is  well  seen  in  the  dog,  that  bolts  his  food;  but 
in  this  and  allied  groups  of  mammals  gastric  digestion  is  very 
activ& 


Bta.  «l-4taBaral«iidtatma«lriro(«dg*B(iaatt(tflerOhurr«M». 


^ 


804 


ANIMAL  PHTSlOIiOOVl 


The  teeth  a- triturating  orgMUi  find  their  h^wt^ej-^^ 
ment  in  ruminants,  the  combined  side-toHnde  and  f orwwd*alid- 
Ckward  motion  of  the  jaws  rendering  them  very  effective. 


r 


\%^^^'^ 


im:: 


tStti ;  T  MoMpM  teeth ;  «,  motai* 

In  Camiwm  the  teeth  serve  for  grasping  and  tearing,  while 
in  the  InseeHvom  the  tongue,  as  also  in  certain  birds  (wood- 
peckers),  is  an  important  organ  for  securing  food. 

It  is  to  be  noted,  too,  that,  while  the  horse  crops  grass  by 
biting  it  off,  the  ox  uses  the  tongue,  as  well  as  the  teeth  and 
lips,  to  secure  the  mouthful; .  '    i 


■!ft??w»w«R«n?7?^ 


DI0K8TI0N  OF  FOOD. 


805 


-»»  «M_nMwmi  vhw  oT  dicMiiw  ■ppwrtfl*  c(  fowl  (aftM*  dukuneMi;.    1,  (wgae;  fi 


80 


806 


ANIMAL  PHT8IOL0OT. 


ot  daoimml  flHcnre :  10,  Meoad  bnuieh  of  mom  ;  11.  oiMb  of  fliMitiiiir  vorttai  of  imwll 
It.  niUl  brtMrtlM ;  ir,  tmniwa  poitlaa  of  thS  lBt(MM,JlM^ 


la,  la,  fTM  eztrHnltlM 
tajba  its,  Nctaan  {  !•, 


It,  lifl  Mm  of  Uw ;  n,  rkritt  lobo ;  II,  nU-blMMer 
daeia;  the  two  paacrMUe  dueU  ai*  !&•  moat  Mitt 


rior,  the  oiMMte  or  bawitie  to  la  tho  Blddla.  and  tha  oyalio  duct  to  iMMlarior :  SL I 
M,  di^ihragnMtto  aaiAtoC  fauw ;  16,  ovaiy  (la  a  rtata  of  aliophrrra^  o*tdiaet. 


Man's  teeth  are  somewhat  intermediate  in  form  between  the 
carnivorous  and  the  herbivorous  type.  Birds  lack  teeth,  but 
the  strong  muscular  gizzard  suffices  to  grind  the  food  against 
the  small  pebbles  that  are  habitually  swallowed. 

The  crop,  well  developed  in  granivorous  birds,  is  a  dilata- 
tion of  the  OBSophagns,  serving  to  store  and  soften  the  food. 

In  the  pigeon  a  glandular  epithelium  in  the  crop  secretes  a 
milky-looking  substance,  that  is  regurgitated  into  the.  mouth 
of  the  young  one,  which  is  inserted  within  that  of  the  parent 
bird. 

The  proventrioulus — an  enlargement  just  above  the  gizzard 
—is  relatively  to  the  latter  very  thin-walled,  but  provides  the 
true  gastric  juicea 

Certain  plants  digest  proteid  matter,  like  animals ;  thus  the 
sun-dew  (Droaera),  by  the  closure  of  its  leaves,  captures  insects, 
which  are  digested  and  the  products  absorbed.  The  digestive 
fluid  consists  of  a  pepsin-containing  secretion,  together  with 
formic  acid. 

Thb  Dioxsnvs  Juicbs. 

l«]ifa.-rThe  saliva  as  fotmd  in  the  month  is  a  mixture  of 
the  secretion  of  three  pairs  of  glands,  alkaline  in  reaction,  of  a 
specific  gravity  of  1009  to  1006,  with  a  small  percentage  of 
solids  ('S  per  cent),  consisting  of  salts  and  organic  bodies 
(mucin,  proteids). 

Saliva  serves  mechanical  functions  in  articulation,  in  moist- 
ening the  food,  and  dissolving  out  some  of  its  salts.  But  its 
principal  use  in  digestion  is  in  reducing  starchy  matters  to  a 
soluble  form,  as  sugar.  So  far  as  known,  the  other  constituents 
of  the  food  are  not  changed  chemically  in  the  mouth. 

Ths  Amflfliytl*  AoUm  of  lidifa.— Starch  exists  in  grains,  sur- 
rounded by  a  ceUvhae  covering,  which  saliva  does  not  digest ; 
hence  its  action  on  raw  starch  is  slow. 

It  is  found  that  if  a  specimen  of  boiled  stuch  not  too  thick 
be  exposed  to  a  small  quantity  of  saliva  at  the  temperature  of 
the  body  or  thereabout  (37*  to  40"  0.),  it  will  speedily  undergo 
certain  changes : 

1.  After  a  very  short  time  sugar  may  be  detected  by  Feh- 


-lAsmma 


DIGESTION  Oir  FOOD. 


807 


Ihk  portiaa  o(  famll 
iMfcedoacMhride 

bis,  free  •xtrMBMc* 
• :  15,  nctnm :  l*. 
|M:n,MU-blMMer; 
laaNtMinoatMit^ 
nops  m* p 
.oviduct. 

u  between  the 
ack  teeth,  but 
e  food  against 

08,  IS  a  dilata-, 
n  the  food, 
crop  secretes  a 
nto  the.  mouth 
;  of  the  parent 

}ye  the  gizzard 
it  provides  the 

mals ;  thus  the 

aptures  insects. 

The  digestive 

together  with 


is  a  mixture  of 
in  reaction,  of  a 
1  percentage  of 
organic  bodies 

lation,  in  moist- 

}  salts.    But  its 

hy  matters  to  a 

her  constituents 

aouth. 

!8  in  grains,  sur- 

does  not  digest ; 

ch  not  too  thick 
9  temperature  of 
peedily  undergo 

letected  by  Fob- 


ling's  solution  (copper  sulphate  in  an  excess  of  sodium  hydrate, 
the  sugar  reducing  the  cupric  hydrate  to  cuprous  oxide  on 
boiling). 

At  this  early  stage  starch  may  still  be  detected  by  the 
blue  color  it  gives  with  iodine ;  but  later,  instead  of  a  blue,  a 
purple  or  red  may  appear,  indicating  the  presence  of  dextrin, 
which  may  be  regarded  as  a  product  intermediate  between 
starch  and  sugar. 

3.  The  longer  the  process  continues,  the  more  sugar  and  the 
less  starch  or  dextrin  to  be  detected;  but,  inasmuch  as  the 
quantity  of  sugar  at  the  end  of  the  process  does  not  exactly 
correspond  with  tiie  original  quantity  of  starch,  even  when  no 
starch  or  dextrin  is  to  be  found,  it  is  believed  that  other  bodies 
are  formed.  One  of  these  is  achroodextrin,  which  does  not  give 
a  color  reaction  with  iodine. 

The  sugars  formed*  are:  (a)  Dextrose,  (b)  Maltose,  which 
has  less  reducing  power  over  solutions  of  copper  salts,  a  more 
pronounced  rotatory  action  on  light,  etc. 

It  is  found  that  the  digestive  action  of  saliva,  as  in  the 
above-described  experiment,  will  be  retarded  or  arrested  if  the 
sugar  is  allowed  to  accumulate  in  large  quantity.  That  diges- 
tion in  the  month  is  substantially  the  same  as  that  just  de- 
scribed can  be  easily  shown  by  holding  a  solution  of  starch  in 
the  mouth  for  a  few  seconds,  and  then  testing  it  for  sugar, 
when  it  will  be  invariably  found. 

While  salivary  digestion  is  not  impossible  in  a  neutral 
medium,  it  is  arrested  in  an  acid  one  even  of  no  great  strength 
(less  than  one  per  cent),  and  goes  on  best  in  a  feebly  alkaline 
medium,  which  is  the  condlUon  normally  in  the  mouth.  Though 
a  temperature  about  equal  to  that  of  the^body  is  best  adapted 
for  salivary  digestion,  it  will  proceed,  we  have  ourselves  found, 
at  a  higher  temperature  than  digestion  by  any  other  of  the 
juices,  so  far  as  man  is  concerned — ^a  fact  to  be  connected,  in  all 
probability,  with  his  habit  for  ages  of  taking  very  warm 
fluids  into  the  mouth. 

The  active  principle  of  saliva  is  ptyalin,  a  nitrogenous  body 
which  is  assumed  to  exist,  for  it  has  never  been  perfectly  iso- 
lated. It  belongs  to  the  class  of  unorganized  ferments,  the 
properties  of  which  have  been  already  referred  to  before  (page 
160). 

OharaoUrirtlos  of  th«  BMirttioii  of  fh*  SiflEwont  CHandi.— Parotid 
saliva  is  in  man  not  a  viscid  fluid,  but  clear  and  limpid,  con<- 
taining  very  little  mucin.  Submaxillary  saliva  in  most  animals 


ANIMAL  PHTSIOLOOT. 


and  in  man  is  viscid,  while  the  secretion  of  the  sublingual 
gland  is  still  more  viscid. 

CoimpuKtit*.— Saliva  differs  greatly  in  activity  in  different 
animals;  thus  saliva  in  the  dog  is  almost  inert,  that  of  the 
pai'otid  gland  quite  so ;  in  the  cat  it  is  but  little  more  effective ; 
and  in  the  horse,  ox,  and  sheep,  it  is  known  to  be  of  very  feeble 
digestive  power. 

In  man,  the  Guinea-pig,  the  rat,  the  hog,  both  parotid  and 
submaxillary  saliva  are  active;  while  in  the  rabbit  the  sub- 
maxillary saliva,  the  re  /erse  of  the  preceding,  is  almost  in- 
active, and  the  parotid  secretion  very  powerful. 

An  aqueous  or  glycerine  extract  of  the  salivary  glands  has 
digestive  properties.  The  secretion  of  the  different  glands 
may  be  collected  by  passing  tubes  or  cannulas  into  thoir  ducts. 

PathologiflaL — Potassium  sulphocyanate  (which  gives  a  red 
color  with  salts  of  iron)  is  sometimes  present  normally,  but  is 
said  to  be  in  excess  in  certain  diseases,  as  rheumatism. 

The  saliva,  normally  neutral  or  only  faintly  acid,  may  be- 
come very  much  so  in  the  intervals  of  digestion  The  rapid 
decay  of  the  teeth  occurring  during  and  after  pregnancy 
seems  in  certain  cases  to  be  referable  in  part  to  an  abnormal 
condition  of  t)ie  saliva,  and  in  part  to  the  drain  on  the  lime 
salts  in  the  construction  of  the  bones  of  the  fostus. 

The  tartar  which  collects  on  the  teeth  consists  largely  of 
earthy  phosphates. 

QMtrie  JoiM. — Qastric  juice  may  be  obtained  from  a  fistu- 
lous opening  into  the  stomach.  Such  may  be  made  artificially 
by  an  incision  over  the  organ  in  the  midcUe  line,  catching  it  up 
and  stitching  it  to  the  edges  of  the  wound,  incising  and  insert- 
ing a  special  form  of  cannula,  which  may  be  closed  or  opened 
at  will.. 

Digestion  in  a  few  cases  of  accidental  gastric  fistulsB  has 
been  made  the  subject  of  careful  study.    The  most  instructive 
case  is  that  of  Alexis  St.  Martin,  a  French  Oanadian,  into^ 
whose  stomach  a  considerable  opening  was  made  by  a  gunshot-  / 
wound. 

Gastric  juice  in  his  case  and  in  the  lower  animals  with  arti- 
ficial openings  in  the  stomach,  has  been  obtained  by  irritating 
the  mucous  lining  mechanically  with  a  foreign  body,  as  a  feather. 

The  great  difficulty  in  all  such  cases  arises  from  the  imjpoB- 
sibility  of  being  certain  that  such  fluid  is  normal ;  for  the  con- 
ditions which  call  forth  secretion  are  certainly  such  as  the 
stomach  never  experiences  in  the  ordinary  course  of  events, 


iMi 


npi 


?^^^5?|^^S| 


DIGESTION  OP  POOD. 


309 


bie  sublingual 

y  in  different 
t,  that  of  the 
aore  effective ; 
of  very  feeble 

h  parotid  and 
ftbbit  the  sub- 
,  is  almost  in-' 

try  glands  has 
fferent  glands 
ito  their  ducts, 
ch  gives  a  red 
Drmally,  but  is 
Latism. 

J  acid,  may  be- 
ion  The  rapid 
fter  pregnancy 
x>  an  abnormal 
kin  on  the  lime 

iUB. 

sists  largely  of 

id  from  a  fistu- 
aade  artificially 
),  catching  it  up 
ising  and  insert- 
dosed  or  opened 

itric  fistidffi  has 
most  instructive 
Canadian,  into*^ 
ie  by  a  gunshot- 1 

limals  with  arti- 
led  by  irritating 
lody,  as  a  feather, 
from  the  impos- 
lal ;  for  the  con- 
nly  such  as  the 
lourse  of  events, 


and  we  have  seen  how  saliva  varies,  according  as  the  animal  is 
fasting  or  feeding,  etc. 

Bearing  in  mind,  then,  that  our  knowledge  is  possibly  only 
approximately  correct,  we  may  state  what  is  known  of  the  se- 
cretions of  the  stomach. 

The  gastric  secretion  is  clear,  colorless,  of  low  specific  grav- 
ity (1001  to  1010),  the  solids  being  in  great  part  made  up  of  pep- 


F»  aw  -GMtric  Biitula  in  caM  of  St.  lUrtin  (aftw  Bewmioiit).  A,  A,  A.B,  borders  of  open- 
IM  i^i^M^rc,  toft  idpple ;  fiTciieirt ;  «  oteaWce.  from  wound  nutde  for i»mo»»l 
o7n^^£)eofoiirtUi«e ;  F,  iff  S\  dcrtrlce*  of  orisUwl  wound. 

sin  with  a  small  quantity  of  mucus,  which  may  become  excess- 
ive in  disordered  conditions.  There  has  been  a  good  deal  of 
dispute  as  to  the  acid  found  in  the  stomach  during  digestion. 
It  is  now  generally  agreed  that  during  the  greater  part  of  the 
digestive  process  there  in  free  hydrochloric  acid  to  the  extent 
of  about  '2  per  cent.  It  is  maintained  that  lactic  acid  exists 
normally  in  the  early  B,\Age»  of  digestion,  and  it  is  conceded 
that  lactie,  butyric,  acetic,  and  other  acid*  may  be  present  in 
certain  forms  of  disordered  digestionr^ 

It  is  also  generally  acknowledged  that  in  mammals  the 
work  of  the  stomach  is  limited,  so  far  as  actual  chemical 
changes  go,  to  tjie  conversion  of  the  proteid  constituents  of 
food  into  peptone.  Fats  may  be  released  from  their  proteid 
coverings  (cells),  but  neither  they  nor  starches  are  in  the  least 
altered  chemically.  Some  have  thought  that  in  the  dog  there 
"    a  slight  digestion  of  fats  in  the  stomach.     The  solvent 


IS 


w^m^^mmm- -^^ 


810 


ANIMAL  PHTSIOLOOT. 


power  of  the  gastric  juice  is  greater  than  can  be  accounted 
for  by  the  presence  of  the  acid  it  contains  merely,  and  it  has 
a  marked  antiseptic  action. 

Digestive  processes  may  be  conducted  out  of  the  body  in  a 
very  simple  manner,  which  the  student  may  carry  out  for 
himself.  To  illustrate  by  the  case  of  gastric  digestion:  The 
mucous  membrane  is  to  be  removed  from  a  pig's  stomach 
after  its  surface  has  been  washed  clean,  but  not  too  thoroughly, 
chopped  up  fine,  and  divided  into  two  parts.  On  one  half  pour 
water  that  shall  contain  "2  per  cent  hydrochloric  acid  (made 
by  adding  4  to  6  cc.  commercial  acid  to  1,000  cc.  water).  This 
will  extract  the  pepsin,  and  may  be  used  as  the  menstruum  in 
which  the  substance  to  be  digested  is  placed.  The  best  is  fresh 
fibrin  whipped  from  blood  recently  shed. 

Since  the  fluid  thus  prepared  wiU  contain  traces  of  peptone 
from  the  digestion  of  the  mucous  membrane,  it  is  in  some 
respects  better  to  use  a  glycerine  extract  of  the  same.  This  is 
made  by  adding  some  of  the  best  glycerine  to  the  chopped-up 
mucous  membrane  of  the  stomach  of  a  pig,  etc.,  well  dried  with 
bibulous  paper,  letting  the  whole  stand  for  eight  to  ten  days, 
filtering  through  cotton,  and  then  through  coarse  filter-paper. 
It  will  be  nearly  colorless,  clear,  and  powerful,  a  few  drops  suf- 
ficing for  the  Work  of  digesting  a  little  fibrin  when  ad  iei  >» 
some  two  per  cent  hydrochloric  acid. 

Digestion  goes  on  best  at  about  40°  C,  but  will  procei  ' 
the  cold  if  the  tube  in  which  the  materials  have  been  placed  is 
frequently  shaken.    It  is  best  to  place  the  test-tube  containing 
them  in  a  beaker  of  water  kept  at  about  blood-heat.    Soon  the 
fibrin  begins  to  swell  and  also  to  melt  away. 

After  fifteen  to  twenty  minutes,  if  a  little  of  the  fluid  in  the 
tube  be  removed  and  filtered,  and  to  the  filtrate  added  carefully 
to  neutralization  dilute  alkali,  a  precipitate,  insoluble  in  water 
but  soluble  in  excess  of  alkali  (or  acid),  is  throwi\  dowou  This 
is  in  most  respects  like  acid-albumen,  but  has  been  called  para- 
peptone.  The  longer  digestion  proceeds,  the  lees  is  there  of 
this  and  the  more  of  another  substance,  peptone,  so  that  the 
former  is  to  be  regarded  as  an  intermediate  product  Peptone 
is  distinguished  from  albuminous  bodies  or  proteids  by — 1. 
Not  being  coagulable  from  its  aqueous  solutions  on  boiling. 
8.  Diffusing  more  readily  through  animal  membranes.  8.  Not 
being  precipitated  by  a  number  of  reagents  that  usually  act 
on  proteids. 

In  artificial  digestion  it  is  noticeable  that  much  more  fibrin 


L  be  accounted 
rely,  and  it  has 

the  body  in  a 
carry  out  for 
digestion:  The 
pig's  stomach 
;oo  thoroughly, 
1  one  half  pour 
ric  acid  (made 
i.  water).  This 
menstruum  in 
he  best  is  fresh 

ices  of  peptone 
it  is  in  some 
same.  This  is 
he  chopped-up 
well  dried  with 
lit  to  ten  days, 
rse  filter-paper, 
k  few  drops  suf- 
when  ad  Je'i    o 

(rill  procet  ' 
been  placed  is 
ube  containing 
leat.    Soon  the 

the  fluid  in  the 
added  carefully 
oluble  in  water 
m  down.  This 
sen  called  para- 
less  is  there  of 
ne,  so  that  the 
duct.  Peptone 
proteids  by — 1. 
ons  on  boiling, 
branes.  8.  Not 
hat  usually  act 

loh  more  fibrin 


DIOBSTION  OP  FOOD.  811 

or  other  proteid  matter  will  be  dissolved  if  it  be  finely  divided 
and  frequently  shaken  up,  so  that  a  greater  surface  is  exposed 
to  the  digestive  fluid. 

The  exact  nature  of  the  process  by  which  proteid  is  changed 
to  peptone  is  not  certainly  known. 

Since  starch  on  the  addition  of  water  becomes  sugar  (C«Hh 
Oi+H|0  =  C«HiiO«),  and  since  peptones  have  been  formed 
through  the  action  of  dilute  acid  at  a  high  temperature  or  by 
superheated  water  alone,  it  is  possible  that  the  digestion  of 
both  starch  and  proteids  may  be  a  hydration;  but  we  do  not 
know  that  it  is  such. 

As  already  explained,  milk  is  curdled  by  an  extract  of  the 
stomach  (rennet) ;  ai^l  this  can  take  place  in  the  absence  of  all 
acids  or  anything  else  that  might  be  suspected  except  the  real 
cause ;  there  seems  to  be  no  doubt  that  there  ia  a  distinct  fer- 
ment which  produces  the  coagulation  of  milk  which  results 
from  the  precipitation  of  its  casein. 

The  activity  of  the  gastric  juice,  and  all  extracts  of  the  mu?i 
cous  membrane  of  the  stomach,  on  proteids,  is  due  to  pepsin,  &j 
nitrogenous  body,  but  not  a  proteid. 

like  other  ferments,  the  conditions  under  which  it  is  effect- 
ive are  well  defined.  It  will  not  act  in  an  alkaline  medium  at 
all,  and  if  kept  long  in  such  it  is  destroyed.  In  a  neutral  me- 
dium its  power  is  suspended  but  not  destroyed.  Digestion  will 
go  on,  though  less  perfectly,  in  the  presence  of  certain  other 
acids  than  hydrochloric.  As  with  all  digestive  ferments,  the 
activity  of  pepsin  is  wholly  destroyed  by  boiling. 

When  a  large  quantity  of  cane-sugar  is  taken  into  the 
stomach,  an  excess  of  mucus  is  poured  out  which  converts  it, 
presumably  by  moamfi  of  a  special  ferment,  into  dextrose. 

nil, — ^The  composition  of  human  bile  is  stated  in  the  fol- 
lowing table: 

Water 8»-90  per  cent. 

Bile^alts 6*11    "     ^ 

Fats  and  soaps. -•    2 

Cholesterin 0*4     "     " 

Lecithin.... :... 1«     "     " 

Mucin 1-8     "     " 

Ash M- 0-61    "     " 

^le  color  of  the  bile  of  man  is  a  rich  golden  yellow.  When 
it  oi^tains  much  mucus,  as  is  tiie  case  when  it  remains  long  in 
the  gall-bladder,  it  is  ropy,  though  usually  dear.  Bile  may 
cont^n  small  quantities  of  iron,  manganese,  and  copper,  the 


^mm» 


m^mmmmmimmamam 


^vr 


312 


ANIMAL  PHY8I0L00T. 


latter  two  especially  being  absent  from  all  other  fluids  of  the 
body.  Sodium  chloride  is  the  most  abundant  salt.  Bile  must 
be  regarded  as  an  excretion  as  well  as  a  secretion ;  the  pig- 
ments, copper,  manganese,  and  perhaps  the  iron  and  the  cho- 
lesterin  being  of  little  or  no  use  in  the  digestive  processes,  so 
far  as  known. 

The  bUe-aaiis  are  the  essential  constituents  of  bile  as  a 
digestive  fluid.  In  man  and  many  other  animals,  they  con- 
sist of  taurocholate  and  glycocholate  of  sodium,  and  may  be 
obtained  in  bundles  of  needle-shaped  crystals  radiating  from 
a  common  center.  These  salts  are  soluble  in  water  and  alco- 
holj  with  an  alkaline  reaction,  but  insoluble  in  ether. 

.Glycocholic  acid  may  be  resolved  into  oholalic  (cholic)  acid 
and  glycin  (glycocoU) ;  and  taurocholio  add  into  cholalic  acid 
and  taurin.    Thus : 

Olyoodtolieacid.  ClHdalle  acid.  Olycte. 

C»H«NO.  +  H,0  =  CkH«0,  +  C,H,NO*. 

IteiroehoUcacid.  CholaUe  add.  Ttortn. 

CwHmNSOt  +  H»  =  CmHmO,  -f  CHfNSO,. 

GlycocoU  (glycin)  is  amido-acetic  acid — 


CH  <^^' 
Taurin,  amido-isethionic  acid. 


and 


SO  H 
CtH4<^m^^»  and  may  be  made  artificially 

from  isethionic  acid. 

It  is  to  be  noted  that  the  bile  acids  both  contain  nitrogen, 
but  that  chololic  acid  does  not.  The  decomposition  of  the  bile 
acids  takes  place  in  the  alimentary  canal,.and  the  glycin  and 
taurin  are  restored  to  the  blood,  and  are  possibly  used  afresh 
in  the  construction  of  the  bile  acids,  though  this  is  not  defi- 
nitely known. 

BUie*PigiiiMits. — ^The  yellowish-red  color  of  the  bile  is  owing 
to  BUirvbin  (OuHnXiOt),  which  may  be  separated  either  as 
an  amorphous  yellow  powder  or  in  tablets  and  prisms.  It  is 
soluble  in  chloroform,  insoluble  in  water,  and  but  partially 
soluble  in  alcohol  and  ether.  It  makes  up  a  large  part  of 
gall-stones,  which  contain,  besides  oholesterin,  earthy  salts  in 
abundance. 

It  may  be  oxidized  to  BiUverdin  (CitHiiN/)4),  the  natural 
green  pigment  of  the  bile  of  the  herbivora.    When  a  drop  of. 
nitric  add,  containing  nitrous  add,  is  added  to  bile,  it  under- 


^.. 


T-r- 


DIGESTION  OF  FOOD. 


818 


ir  fluids  of  the 
It.  Bile  must 
Btion ;  the  pig- 
and  the  cho- 
re processes,  so 

of  bile  as  a 
(nals,  they  con- 
m,  and  may  be 
radiating  from 
irater  and  alco- 
»ther. 

lie  (oholic)  acid 
ito  cholalic  acid 


rein, 
win. 


nade  artificially 


intain  nitrogen, 
ition  of  the  bile 
the  glycin  and 
ibly  used  afresh 
this  is  not  defi> 

le  bile  is  owing 
irated  either  as 
i  ptisms.  It  is 
d  but  partially 
a  large  part  of 
earthy  salts  in 

O4),  the  natural 
Wihen  a  drop  of. 
0  bile,  it  under- 


goes a  series  of  color  changes  in  a  certain  tolerably  constant 
order,  becoming  green,  greenish-blue,  blue,  violet,  a  brick  red, 
and  finally  yellow;  though  the  green  is  the  most  characteristic 
and  permanent.  Bach  one  of  these  represents  a  distinct  stage 
of  the  oxidation  of  bilirubin,  the  green  answering  to  biliverdin. 
Such  is  Omelin's  test  for  bile-pigments,  by  which  they  Inay  be 
detected  in  urine  or  other  fluids.  CJhej^bsence  of  proteids  in 
Wle^iSJtoJ)enotedj/  " 

Tha  IMgwttfa  At/Om  of  BUa.— ^li^So  far  ais  known,  its  action 
on  proteids  is  niL  When  bile  is  added  to  the  products  of  an 
artificial  gastric  digestion,  bile-salts,  peptone,  pepsin,  and  para- 
peptone  are  precipitated  and  redissolved  by  excess.  2.  It  is 
slightly  solvent  of  fats,  though  an  emulsion  made  with  bile,  is 
very  feeble.  But  it  is  likely  helpful  to  pancreatic  juice,  or 
more  efficient  itself  when  the  latter  is  present.  With  free  f Jttty 
acids  it  forms  soaps,  which  themselves  help  in  emulsifying  fat. 
3.  Membranes  wet  with  bile  allow  fats  to  pass  more  readily ; 
hence  it  is  inferred  that  bile  assists  in  absorption.  4.  When^ 
bile  is  not  poured  out  into  the  alimentary  canal  whe  faeces  i 
become  clay-colored  and  ill-smelling,  foul  gases  being  secretedj 
in  abundance,  so  that  it  would  seem  that  bile  exercises  an  anti- 
septic influence.  It  may  limit  the  quantity  of  indal  formed. 
It  is  to  be  understood  that  these  various  properties  of  bile  are 
to  be  traced  almost  entirely  to  its  salts ;  though  its  alkaline 
reaction  is  favorable  to  digestion  in  the  intestines,  apart  from 
its  helpfulness  in  soap-forming,  etc.  6.  (R  is  thought  by  some 
that  the  bile  acts  as  a  stimulant  to  the  intestinal  tract,  giving 
rise  to 'peristaltic  movements,  and  also,  mechanically,  as  a  lubri- 
cant of  the  f  CBces.  ^  the  opinion  of  many,  an  excess  of  bile 
naturally  poured  out  causes  diarrhoea,  and  it  is  well  known 
that  bile  given  by  the  mouth  acts  as  a  pturgative.  However, 
we  must  distinguish  between  the  action  of  an  excess  and  that 
of  the  quantity  secreted  by  a  healthy  individual.  The  acid  of 
the  stonukch  has  probably  no  effect  allied  to  that  probuced  by 
giving  acids  medicinally,  which  warns  ns  that  too  much  must 
not  be  made  out  of  the  argument  from  bilious  diarrhoea.  6./^ 
before  intimated,  a  great  part  of  the  bile  must  be  regardecTas 
excrementitious.  It  looks  as  though  much  of  the  effete  heemo- 
globin  of  the  blood  apd  of  the  cholesterin,  which  represents 
possibly  some  of  the  waste  of  nervous  metabolism,  were  expelled 
from  the  body  by  the  bile.  The  cholalic  acid  of  the  faeces  is 
derived  from  the  deoompcsition  of  the  bile  acids.  Part  of  their 
mucus  must  also  be  referred  to  the  bile,  the  quantity  originally 


8U 


ANIMAL  PHTSIOLUGY. 


present  in  this  fluid  depending  much  on  the  length  of  its  stay 
in  the  gall-bladder,  which  secretes  this  substance.  7.  There  is 
throughout  the  entire  alimentary  tract  a  secretion  of  mucus 
which  must  altogether  amount  to  a  large  quantity,  and  it  has 
been  suggested  that  this  has  other  than  lubricating  or  such  like 
functions.  It  appears  that  mucus  may  be  resolved  into  a  pro- 
teid  and  an  aniitial  gum,  which  latter,  it  is  maintained,  like 
vegetable  gums,  assists  emulsification  of  fats.  If  this  be  true, 
and  the  bile  is,  as  has  been  asserted,  possessed  of  the  power  to 
break  up  this  mucus  (mucin),  its  emulsifying  effect  in  the  in- 
testine may  indirectly  be  considerable.  Bile  certainly  seems 
to  intensify  the  emulsifying  power  of  the  pancreatic  juice. 

There  does  not  seem  to  be  any  ferment  in  bile,  unless  the 
power  to  change  starch  into  sugar,  peculiar  to  this  secretion  in 
some  animals,  is  owing  to  such. 

Compmtif*.— The  bile  of  the  cwnivora  and  omnivora  is 
yellowish-red  in  color ;  that  of  herbivora  green.  The  former 
contains  taurocholate  salts  almost  exclusively ;  in  herbivorous 
animals  and  man  there  is  a  mixture  of  the  salts  of  both  acids, 
though  the  glycocholate  predominates. 


Fm.  a88.-aftn-btadder,  ductua  diotodoahai  moAmm'MB  (•»«  Le^toiv 


"6,  iMVMttia  diMt ;  e.  bpenlnt  of  Moood  duot  ot 
duataiidbil»4uot;  «,«,ffikNlMiQ 


r,f. 


«H  (aftflr  Le  Bon),  a,  MiMitaddar ; 
MM ;  d,  <veiiii«  of  nwrn  pMwrMktie 
jdoonM ;  p,  vaaanaa. 


FaaorMtte  Jniiot.— This  fluid  is  found  to  vary  a  good  deal 
quantitatively,  according  as  it  is  obtained  from  a  temporary 
(freshly  made)  or  permanent  fistular— a  fact  which  emphasises 


Bi 


DIGESTION  OF  FOOD. 


815 


h.  of  its  stay 
7.  There  is 
>n  of  mucus 
f,  and  it  has 
f  or  such  like 
d  into  a  pro- 
ntained,  like 
this  be  true, 
the  power  to 
ct  in  the  in- 
tainly  seems 
tic  juice. 
ie,  unless  the 
a  secretion  in 

omnivora  is 

The  former 

herbivorous 

>f  both  acids. 


I),   a,  MlMitaddar; 
of  miun  pMwrMtie 

r  a  good  deal 

a  temporary 

ih  emphasiies 


the  necessity  for  caution  in  drawing  conclusions  about  the 
digestive  juices  as  obtained  by  our  present  methods. 

The  freshest  juice  obtainable  through  a  recent  fistulous 
opening  in  the  pancreatic  duct  is  clear,  colorless,  viscid,  alka- 
line in  reaction,  and  with  a  very  variable  quantity  of  solids 
(two  to  ten  per  cent),  less  than  one  per  cent  being  inorganic 
matter. 

Among  the  organic  constituents  the  principal  are  albumin, 
alkali-albumin,  peptone,  leucin,  tyrosin,  fats,  and  soaps  in  small 
amount.   The  alkalinity  of  the  juice  is  owing  chiefly  to  sodium 


#.' 


* 


:■¥ 


Vto.  M.-0lf3riUlii  Of  leudn  (Ftanke). 


Fre.  a70.-Or]ratala  of  tyitMiii  (rmike). 


carbonates,  which  seem  to  be  associated  with  some  proteid 
body.  There  is  little  doubt  that  leucin,  tyrosin,  and  peptone 
arise  from  digestion  of  the  proteids  of  the  juice  by  its  own 
action. 

liptriaMBtiL— If  the  pancreatic  glands  be  mostly  freed  from 
adhering  fat,  cut  up, and  washed  so  as  to  get  rid  of  blood; 
then  minced  as  fine  as  possible,  and  allowed  to  stand  in  one-per- 
cent sodium-carbonate  solution  at  a  temperature  of  40°  C,  the 
following  results  may  be  noted:  1.  After  a  variable  time  the 
reaction  may  change  to  acid,  owing  to  free  fatty  acid  from 
the  decomposition  (digestion)  of  neutral  fats.  2.  Alkali-albu- 
min,  or  a  body  closely  resembling  it,  may  be  detected  and  sep- 
arated by  neutralization.  8.  Peptone  may  be  detected  by  the 
use  of  a  trace  of  copper  sulphate  added  to  a  few  drops  of  caustic 
alkali,  which  becomes  red  if  this  body  be  present.  4.  Alter  a 
few  hours  the  smell  becomes  feecal,  owing  in  part  to  indd, 
which  gives  a  violet  color  with  chlorine-water;  while  under 
the  microscope  the  digesting  mass  may  be  seen  to  be  swarming 


'imimis^& 


■mmummi&nMmmi'Mmm&'mm 


r 


816 


ANIMAL  PHYSIOLOGY. 


with  bacteria.  5.  When  digestion  has  proceeded  for  some  time, 
leucin  and  tyroain  may  be  shown  to  be  present,  though  their 
satisfactory  separation  in  crystalline  form  involves  somewhat 
elaborate  details.  These  changes  are  owing  to  self-digestion 
of  the  gland. 

All  the  properties  of  this  secretion  may  be  demonstrated 
more  satisfactorily  by  making  an  aqueous  or,  better,  glycerine 
extract  of  the  pancreas  of  an  ox,  pig,  etc.,  and  carrying  on  arti- 
ficial digestion,  as  in  the  case  o*  a  peptic  digestion,  with  fibrin. 
In  the  CMC  of  the  digestion  of  iat,  the  emulsifying  power  of  a  < 
watery  extract  of  the  gland  may  be  shown  by  shaking  up  a 
little  melted  hog's  lard,  olive-oil  (each  quite  fresh,  so  as  to  show 
no  acid  reaction),  or  soap.  Kept  under  proper  conditions,  free 
acid,  the  result  of  decomposition  of  the  neutral  fats  or  soap 
into  free  acid,  etc.,  may  be  easily  shown.  The  emulsion,  though 
allowed  to  stend  long,  persists,  a  fact  which  is  availed  of  to 
produce  more  palatable  and  easily  assimilated  preparations  of 
cod-liver  oil,  etc.,  for  medicinal  use. 

Starch  is  also  converted  into  sugar  with  great  ease.  ^ 
short,  the  digestive  juice  of  the  pancreas  is  the  most  complex 
and  complete  in  its  action  of  the  whole  series.  It  is  amyloljrtic, 
proteolytic,  and  steaptic,  and  these  powers  have  been  attributed 
to  three  distinct  termentar—amylopain,  trypsin,  and  steapain. 

Proteid  digestion  is  carried  further  tlum  by  the  gastric  juice, 
and  the  quantity  of  crystalline  nitrogenous  products  formed  is 
in  inverse  proportion  to  the  amount  of  peptone,  from  which  it 
seems  just  to  infer  that  part  of  the' original  peptone  has  been 
converted  into  these  bodies,  which  are  fouud  to  be  abundant  or 
not  in  an  artificial  digestion,  according  to  the  length  of  time 
it  has  lasted — ^the  longer  it  has  been  under  way  the  more  leucin  ' 
and  tyrosin  present.  Leucin  is  another  compound  into  which 
the  amido(NH«)  group  enters  to  make  amido-caproic  acid— one 
of  the  fatty  series — ^while  tyrosin  is  a  very  complei^  member  of 
the  aromAtic  series  of  oompound&  CfkxM  complicated  are  the 
chemical  effects  of  the  digestive  jmces;  and  it  seems  highly 
probable  that  these  are  only  some  of  the  compounds  into 
which  the  proteid  is  broken  up. 

These  crystalline  bodies  may  be  made  artificially  by  the 
long-continued  action  under  heat  of  aoi^s  and  alkalies,  in  pro- 
teid or  gelatinous  matter,  though  it  can  not  be  said  that  these    / 
facts  have  as  yet  thrown  much  light  upon  their  formation  inr^ 
the^digestive  organs, 
/^ough  putrefactive  changes  with  formation  of  indd,  etc.. 


ei¥i 


DIQBSTION  OF  FOOD. 


817 


or  some  time, 
though  their 
res  somewhat 
self -digestion 

lemonstrated 
ter,  glycerine 
ying  on  arti- 
i,  with  fibrin, 
g  power  of  a 
haking  up  a 
so  as  to  show 
nditions,  free 
fats  or  soap 
ilsion,  though 
availed  of  to 
eparations  of 

eat  ease.  (Si 
Qost  complex 
is  amylolytic, 
len  attributed 
d  steapsin. 
gastric  juice, 
icts  formed  is 
rom  which  it 
one  has  been 
I  abundant  or 
>ngth  of  time 
B  more  leucin  ' 
d  into  which 
oic  acid— one 
91^  member  of 
B&ted  are  the 
seems  highly 
aponnds  into 

oially  by  the 
kalies,  in  pro- 
id  that  these   / 
formation  inr-*" 

of  indol,  etc.. 


occur  in  pancreatic  digestion,  both  within  and  without  the 
body,  they  are  to  be  regarded  as  accidental,  for  by  proper  pre- 
cautions digestion  may  be  carried  on  in  the  laboratory  without 
their  occurrence,  and  they  vary  in  degree  with  the  animal,  tha 
individual,  the  food,  and  other  conditions.    It  is  not,  however. 


M 


v/* 


*oftl 


/ 


■® 


FM.  sn.-lIicr«M>rKMitania  of  bus*  taitefiiM  (^»«.I*»«2^):_.ilJ**l2*™-?*?  cimmmiie ; 

a,  bMterinm  tacUa  •BroseoM;  «.  4.  bwge.lMettU  of  Mewrtock,  wltih  iMrtial  endoMnous 

,  not«-tomuktiaa ;  5,  tuIoih  «UfM  <rf  dsvelopawiit  o<  bMsOIu*  which  cmmm  fermentation 

ocelbu 


to  be  inferred  that  micro-organisms  serve  no  useful  purpose 
in  the  alimentary  canal ;  the  subject,  in  fact,  requires  further 
investigation. 

Imoinu  Bnterisaa. — ^The  difficulties  of  collecting  the  secretions 
of  Lieberk&hn's,  Br&nner's,  and  other  intestinal  glands  will  be 
at  once  apparent.  But  by  dividing  the  intestine  in  two  places, 
so  as  to  isolate  a  loop  of  the  gut,  joining  the  sundered  ends  by 
ligatures,  thus  making  the  continuity  of  the  main  gut  as  com- 
plete as  before,  closing  one  end  of  the  isolated  loop^  and  bring- 
ing the  other  to  the  exterior,  as  a  fistulous  opening,  the  secre- 
tions could  be  collected,  food  introduced,  etc. 

But  it  seems  highly  improbable  that  information  approxi- 
mately correct  at  best,  and  possibly  highly  misleading,  could 
be  obtained  in  such  manner.    Moreover,  the  greatest  diversity) 
of  opinion  prevails  as  to  the  facts  thmnselves,  so  that  it  seems) 
scarcely  worth  while  to  state  the  contradictory  conclusions^ 
arrived  at.  , 

(^  is,  however,  oil  the  face  of  it,  probable  that  the  intestine 
—even  the  large  intestine— does  secrete  juices,  tiiat  in  herbiv- 
ora,  at  all  events,  play  no  unimportant  part  in  the  digestion 
of  their  bulky  food;  and  it  is  also  i»obable,  as  in  so  many 
other  instances,  that,  ,when  the  other  parts  of  the  digestive 
tract  faU,  when  the  usual  secretions  are  not  prepared  or  do  not 
act  on  the  food,  glands  that  normally  play  a  possibly  insig- 
nificant part  may  f  imction  excessively— we  may  almost  say 
vicariously — and  that  such  glands  must  be  sought  in  the  small 
intestine.    There  are  facts  in  clinical  medicine  that  seem  to 


fcWiiiiaittiiiiMmiiB^'iy 


DIGESTION  OF  FOOD. 


819 


point  strongly  in  this  direction,  though  the  subject  has  not  yet 
been  reduced  to  scientific  form. 

GoBfinttvt.— Within  the  last  few  years  the  study  of  vege- 
table assimilation  from  the  comparative  aspect  has  been  fruit- 
ful in  results  which,  together  with  many  other  facts  of  vege- 
table metabolism,  show  that  even  plants  ranking  high  in  the 
organic  plane  are  not  in  many  of  their  functions  so  different 
from  animals  as  has  been  supposud.  It  has  been  known  for  a 
longer  period  that  certain  plants  are  -carnivorous ;  but  it  was 
somewhat  of  a  surprise  to  find,  as  has  been  done  within  the 
past  few  years,  that  digestive  ferments  are  widely  distributed 
in  the  vegetable  kingdom  and  are  found  in  many  different 
parts  of  plants.  What  purpose  they  may  serve  in  the  vege- 
table economy  is  as  yet  not  well  known.  At  present  it  would 
seem  as  though,  from  their  presence  in  so  many  cases  in  the 
seed,  they  might  have  somethihg  to  do  with  changing  the 
cruder  forms  of  nutriment  into  such  as  are  better  adapted  for 
the  nourishment  of  the  embryo. 

Thus  far,  then,  not  only  diastase  but  pepsin,  a  body  with 
action  similar  to  trypsin,  and  a  rennet  ferment,  rank  among 
the  vegetable  ferments  best  known. 

A  ferment  has  been  extracted  from  the  stem,  leaves,  and  un- 
ripe  fruit  of  Carica papaya, found  in  the  East  and  West  Indies^ 
and  elsewhere,  which  has  a  marked  proteolytic  action. 

It  is  effective  in  a  neutral,  most  so  in  an  alkaline  medium ; 
and,  though  its  action  is  suspended  in  a  feeble  acid  menstruum, 
it  does  not  f«ppear  to  be  destroyed  under  such  circumstances,  as 
is  trypsin.  This  body  is  attracting  a  good  deal  of  attention, 
and  its  use  has  been  recently  introduced  into  medical  practice. 

Very  lately  also  a  vegetable  rennet  has  been  found  in  sev- 
eral species  of  plants.    The  subject  is  highly  promising  and! 
suggestive. 


tndgrMti 

D,  CMOum ;  E.F,0, 

UdooptodiwSled  to 


Secretion  as  a  Physiological  Process. 

BMntton  of  fhs  laliTary  OIuids.r-We  shall  treat  this  subject 
at  more  length  because  of  the  light  it  throws  on  the  nervous 
phenomena  of  vital  process ;  and,  since  the  salivary  glands  have 
been  studied  more  thoroughly  and  successfully  than  any  other, 
they  will  receive  greater  attention. 

The  main  facts,  ascertained  experimentally  and  otherwise, 
axe  the  following : 

A«mTning  that  the  student  is  familiar  with  the  general  ana- 


■M 


no 


AKIMAL  PHTSIOLOOY. 


1 

1 


tomical  relations  of  the  salivary  glands  in  some  mammal,  we 
would  further,  remind  him  that  the  submaxillary  gland  has  a 
double  nervous  supply :  1.  From  the  cervical  sympathetic  by 
branches  passing  to  the  gland  along  its  arteries.  2.  From  the 
chorda  tympani  nerve,  which  after  leaving  the  facial  makes 
connection  with  the  lingual,  whence  it  proceeds  to  its  destina- 
tion. 


Fort «/ brain  atom  iMduaa 


framtonQM 


gtond 


Stood  VMMl 

c/fflaful 


Smxrlor  un,  oimoifon 


StfrnpoOMlile 


Ito.  STl—Diagnm  iatewled  to  indicate  the  twrroiM  mediaiiiam  of  MlinuT  1^^ 

(The  following  facts  are  of  importance  as  a  basis  for  conclu- 
sions :  1.  It  is  a  matter  of  common  observation  that  a  flow  of 
saliva  may  be  excited  by  the  smell,  taste,  sight,  or  even  thought 
of  food.  2.  It  is  also  a  matter  of  experience  that  emotions,  as 
fear,  anxiety,  etc.,  may  parch  the  mouth— i.  e.,  arrest  the  flow  of 
saliva.    The  excited  speaker  thus  suffers  in  his  early  efforts. 


)  mammal,  we 
ry  gland  has  a 
apathetic  by 
2.  From  the 
facial  makes 
to  its  destina- 


otow  imduna 


BbNNfVMMl 

cffHand 


langlfon 


MUwyMeretkm. 

lasis  for  coDclu- 
L  that  a  flow  of 
3r  ever  thought 
at  emotions,  as 
rresttheflowof 
Lis  early  efforts. 


DIGESTION  OF  FOOD. 


891 


3.  If  a  glass  tube  be  placed  in  the  duct  of  the  gland  and  any 
substance  that  naturally  causes  a  flow  of  saliva  be  placed'  on 
the  tongue,  saliva  may  be  seen  to  rise  rapidly  in  the  tube.  4. 
The  same  may  be  observed  if  the  lingual  nerve,  the  glossopha- 
ryngeal, and  many  other  nerves  be  stimulated ;  also  if  food  be 
introduced  into  the  stomach  through  a  fistula.  6.  If  the  pe- 
ripheral end  of  the  chorda  tympani  be  stimulated,  two  results 
follow :  (a)  There  is  an  abundant  flow  of  saliva,  and  (6)  the 
arterioles  of  the  gland  become  dilated ;  the  blood  may  pass 
through  with  such  rapidity  that  the  venous  blood  may  be 
bright  red  in  color  and  there  may  be  a  venous  pulse.  7.  Stimu- 
lation of  the  medulla  oblongata  gives  rise  to  a  flow  of  saliva, 
which  is  not  possible  when  the  nerves  of  the  gland,  especially 
the  chorda  tympani,  are  d:  vided ;  nor  can  a  flow  be  then  excited 
by  any  sort  of  nervous  sti  lulation,  excepti';ig  that  of  the  ter- 
minal branches  of  the  net'  es  of  the  gla  .d  itself.  8.  If  the  sym- 
pathetic nerves  of  the  gland  be  divided,  there  is  no  immediate 
flow  of  saliva,  though  there  may  be  some  dilatation  of  its  ves- 
sels. 9.  Stimulation  of  the  i^erminal  ends  of  he  sympathetic 
and  chorda  nerves  causes  a  flow  of  saliva,  d^ "  ring  as  to  total 
qimntity  and  the  amount  of  contained  &»ii<ls;  but  the  nerve 
that  produces  the  more  abundant  ^at^ry  secretion,  •*  the  re- 
verse, varies  with  the  animal,  e.  g ,  lu  tihe  cat  chorciti.  saliva  is 
more  viscid,  in  the  dog  less  so;  t  tougii  in  all  animals  as  y<^t 
examined  it  seems  that  the  secretion  as  a  result  of  stimulatioi; 
of  the  chorda  tympani  nerve  is  the  more  abundant ;  and  in  the 
case  of  stimulation  of  the  chorda  the  vessels  of  the  gland  are 
dilated,  while  in  the  case  of  the  sympathetic  they  are  con- 
stricted. 10.  If  atropin  be  injecte  I  into  the  blood,  it  is  impos- 
sible to  induce  salivary  secretion  by  any  form  of  stimulation, 
though  excitation  of  the  chorda  nerve  still  causes  arterial  dila. 
tation. 

OwalMtonfc — 1.  (There  is  a  center  in  the  medulla  presiding 
over  salivary  secretion,  fi.  The  influence  of  this  ceaier  is 
rendered  effective  tL.  r^^h  the  chorda  tyinpani  nerve  at  all 
events,  if  not  also  bj  i'rM  sympathetic.  3.  Tbe  chorda  tym- 
pani nerve  contains  both  secretory  and  vaso-dilator  fibers ;  the 
sympathetic  secretory  and  vaso-constrictor  fibers.  4.  Arterial 
change  is  not  esst n  tial  to  secretion,  though  doubtless  it  usually 
accompanies  i ..  Secretion  may  be  induced  in  the  glands  of 
an  animal  after  decapitation  by  stimulation  of  its  chorda 
tympani  nerve,  analogous  to  the  secretion  of  sweat  in  the  foot 
of  «k  recently  dead  animid,  under  stimulation  of  the  sciatic 

81 


»'Maaa!i**^:;.v^iua8fefe;«^ 


ll 


322 


ANIMAL  PHTSIOLOGT. 


nerve.  5.'  The  character  of  the  saliva  secreted  varies  with 
the 'nerve  stimulated,  so  that  it  seems  likely  that  the  nervous 
centers  normally  in  the  intact  animal  regulate  the  quality  of 
the  saliva  through  the  degree  to  which  one  or  the  other  kind 
of  nerves  is  called  into  action.  6.  Secretion  of  saliva  may 
be  induced  reflexly  by  experiment,  and  such  is  probably  the 
normal  course  of  events.  7.  The  action  of  the  medullary  center 
I  may  be  inhibited  by  the  cerebrum  (emotions). 

Some  have  located  a  center  in  the  cerebral  cortex  (taste  cen- 
ter), to  which  it  is  assumed  impulses  -first  travel  from  the' 
tongue  and  which  then  rouses  the  proper  secreting  centers  in 
the  medulla  into  activity.  It  seems  more  likely  that  the  corti- 
cal center,  if  there  be  one,  completes  the  physiological  processies 
by  which  taste  sensations  are  elaborated. 

From  the  influence  of  drugs  (atropin  and  its  antagonist 
pilocarpin)  it  is  plain  that  the  gland  can  be  affected  through 
the  blood,  though  whether  wholly  by  direct  action  on  the  cen- 
ter, on  any  local  nervous  mechanism  or  directly  on  the  cells,  is 
as  yet  undetermined.  It  is  found  that  pilocarpin  can  act  long 
after  section  of  the  nerves.  This  does  not,  however,  prove  that 
in  the  intact  animal  such  is  the  tzsual  modus  operandi  of  this 
or  other  drugs,  any  more  than  the  so-called  paralytic  secretion 
after  the  section  of  nerves  proves  that  the  latter  are  not  con- 
cerned in  secretion. 

__  Wfltjookjagon^aralytic  secretion  as  the  work  of  the  cells 
Qwhen  g^ej!nx)ng---iwsiied3rom  under'The  "^ 
nerve-centers."  ^Secretion  is  a  part  of  the  iiaturaTTife^processes 
orgTand-cells — we  may  say  a  series  in  the  long  chain  of  pro- 
cesses which  are  indispensable  for  the  health  of  these  cells. 
They  must  be  either  secreting  cells,  or  have  no  place  in  the  nat- 
ural order  of  things.  It  is  to  be  especially  noted  that  the  secre- 
tion of  saliva  continues  when  the  pressure  in  the  ducts  of  the 
gland  is  greater  than  that  of  the  blood  in  its  vessels  or  even 
of  the  carotid ;  so  that  it  seems  possible  that  over-importance 
has  been  attached  to  blood  •  pressure  in  secretory  processes 
generally. 

It  may,  then,  be  safely  assumed  that  formation  of  saliva  re- 
sults in  consequence  of  the  natural  activity  of  certain  cells,  the 
processes  of  which  are  correlated  and  harmonized  by  the  nerv- 
ous system ;  their  activity  being  accompanied  by  an  abundant 
supply  of  blood.  The  actual  outpouring  of  saliva  depends  usu- 
ally on  the  establishment  of  a  nervous  reflex  arc.  The  other 
glands  have  been  less  carefully  studied,  but  the  parotid  is 


i  varies  with 
it  the  nervous 
the  quality  of 
she  other  kind 
)f  saliva  may 
probably  the 
iduUary  center 

'tex  (taste  cen- 
ivel  from  the' 
ing  centers  in 
that  the  corti- 
igical  processes 

its  antagonist 
Eected  through 
ion  on  the  cen- 
on  the  cells,  is 
in  can  act  long 
iver,  prove  that 
perandi  of  this 
alytic  secretion 
er  are  not  con- 

ork  of  the  cells 
)minion  of  the 
ftTlife^processes 
Lg  chain  of  pro- 
i  of  these  cells, 
place  in  the  nat- 
d  that  the  secre- 
the  ducts  of  the 
I  vessels  or  even 
jver-importance 
retory  processes 

bion  of  saliva  re- 
certain  cells,  the 
zed  by  the  nerv- 
by  an  abundant 
iva  depends  usu- 
arc.  The  other 
t  the  parotid  is 


known  to  have  a  double  nervous  supply  from  the  cerebro- 
spinal and  the  sympathetic  systema 

It  would  appear  that,  as  the  vaso-motor  changes  run  paral- 
lel with  the  secretory  ones,  the  vaso-motor  and  the  propei* 
secretory  centers  act  in  concert,  as  we  have  seen  holds  of  the 
former  and  the  respiratory  center.  But  it  is  to  our  own  mind 
very  doubtful  whether  the  doctrine  of  so  sharp  a  demarkation 
of  independent  centers,  prominently  recognized  in  the  j)hysi- 
ology  of  the  day,  will  be  that  ultimately  accepted. 

Seoretion  by  the  StonuudL — The  mucous  membrane  of  St.  Mar- 
tin's stomach  was  observed  to  be  pale  in  the  intervals  of  diges- 
tion, but  flushed  when  secreting,  which  resembled  sweating,  so 
far  as  the  flow  of  the  fluid  is  concerned.  When  the  man  was 
irritated,  the  gastric  membrane  became  pale,  and  secretion  was 
lessened  or  arrested,  and  it  is  a  common  experience  that  emo- 
tions may  help,  hinder,  or  even  render  aberrant  the  digestive 
processes. 

(^Piile  the  evidence  is  thus  clear  that  gastric  secretion  is 
regulated  by  the  nervous  system,  the  way  in  which  this  is 
JEhCcomplished  is  very  obscure.  We  know  little  of  either  the 
centers  or  nervM~cbncer]iec[7and  what  we  do  know  helps  but 
doubtfully  to  an  understanding  of  the  matter,  if,  indeed,  it 
does  not  actually  confuse  and  puzzle. 

(Pigestion  can  proceed  in  a  fashion  after  section  of  the  nerves 
going  to  the  stomach,  though  this  has  little  force  as  an  argu- 
ment against  nerve  influence.  We  may  conclude  the  subject, 
by  stating  that,  while  the  influence  of  the  nervous  system  over 
gastric  secretion  is  undoubted  as  a  fact,  the  method  is  not 
understood;  and  the  same  remark  applies  to  the  secreting 
activity  of  the  liver  and  pancreas. 

Tht  iMntba  of  Bil*  ud  Vnatmtia  JTviM.— When  the  contents 
of  the  stomach  have  reached  the  orifice  of  the  discharging  bile- 
duct,  a  large  flow  of  the  biliary  secretion  takes  place,  probably 
as  the  result  of  the  emptying  of  the  gall-bladder  by  the  con- 
traction of  its  walls  and  those  of  its  ducts.  This  is  probably 
a  reflex  act,  and  the  augmented  flow  of  bile  when  digestion  is 
proceeding  is  also  to  be  traced  chiefly  to  nervous  influences 
reaching  the  gland,  though  by  what  nerves  6t  under  the  gov- 
ernment of  what  part  of  the  nervous  centers  is  unknown^ 
Very  similar  statements  apply  to  the  secretion  of  the  pancre- 
atic glands,  though  this  is  not  constant,  as  in  the  case  of  bile— 
at  all  events,  in  most  animals. 

'It  is  known  that  after  food  has  been  taken  there  is  a  sudden 


V(«iMiEir.«4.~'J>»l'**«w*"  ■ 


mkmmmum 


mmm 


w 


WM|NMP*<I 


8M 


ANIMAL  PHTSI0L06Y. 


increase  in  the  quantity  of  bile  secreted,  followed  by  a  sudden 
diminution,  then  a  more  gradual  rise,  with  a  subsequent  fall. 
Almost  the  same  holds  for  the  pancreas. 


tjO 


8J 


U 


3.4 


Vt 


10 


L8 


M 


tA 


U 


IJO 


u 


u 


u 


IJi 


IX 


M 


M 


0.1 


IJ 


z^^ 


H6lll|.    Tan  mm 
gnnimNoC 


llll»l*l(H«l7l»HH0immaMH6lMlll«l8l4l5l»l7l8l>'liDl 

food ;  tranalM  Mlioimt  In  eoMe  o«m- 


NHCMiitiioiiri  after  taking  1       

■  m  tan  mlwiten.   Vood  waa  takan  at  B  and  O. 
i&aMsraUModitla. 


1kiidiaiiramT«7 


(It  seems  impossible  to  explain  these  facts,  especially  the 
first  rapid  discharge  of  fluid  apart  from  the  direct  influence  of 
the  nervous  system. 

(Upon  the  whole,  the  evidence  seems  to  show  that  tiie  press* 
ure  in  the  bilenluctB  is  greater  than  in  the  veins  that  unite  to 
make  up  the  portal  system ;  but  there  are  difficulties  in  the 
investigation  of  such  and  kindred  subjects  as  regards  the  liver, 
owing  to  its  peculiar  vascular  supply.  It  wiU  be  borne  in  mind 
that  the  liver  in  mammals  oonsUrtM  of  a  mass  of  blood-vessels, 
between  the  meshes  of  which  are  packed  innumerable  cells,  and 
that  around  the  latter  meander  the  bile  oapillaviee;  that  the 
portal  vem  breaks  up  into  the  interlobular,  from  which  capil- 
laries arise,  that  terminate  in  the  central  intralobular  veins, 
which  make  up  the  hepatic  veiuletoor  termiiiate  in  these  vessels 
But  the  structure  is  complicated  l^  Uie  branches  of  the  hepatic 
artery,  which,  an  arterioles  and  capillaries,  enters  to  some  extent 
into  the  formation  of  the  lobtilar  vessels.  It  is  remarkable  that^ 
the  cells  of  the  liver  are  so  similar,  considering  the  complicate^ 
functions  they  appear  to  discharge. 


•«<«•*<■*■ 


DIOBSnON  OF  FOOD. 


886 


I  by  a  sudden 
bsequent  fall. 


«l7lBl»H0 


■IM  (after  N. 

■BOimt  In  cat 

7.   TlilidiM'Mn^'VT 


especially  the 
K3t  inflnecce  of 

that  i&e  press* 
is  that  unite  to 
ftculties  in  the 
l^rds  the  liver, 
borne  in  mind 
f  blood-vessels, 
»rable  cells,  and 
KtieB',  that  the 
•m  which  capil- 
alobular  veins, 
in  these  vessels 
B  of  the  hepatic 
I  to  some  extent 
emarkable  that^ 
the  complicate^ 


(X  question  of  interest,  though  difficult  to  answer,  is  the 
extent  to  which  the  various  constituents  of  bile  are  manufact- 
ured in  the  liver.    Taurin,  for  example,  is  present  in  some  of 


I 


MMm:  I, «, 1. 1. taMoMv ' 
AIM  with  ft  daik  injMlioii. 


Si 


itadBCtadwHh 


;A»,».».»,1 


thd  tissues,  but  whether  tiliis  is  used  in  the  manufacture  of 
taurocholic  acid  or  whether  the  latter  is  made  entirely  anew, 
and  possibly  by  a  method 
in  which  taurin  never  ap- 
pears as  such,  is  an  open 
question.  It  is  highly  prob- 
able that  a  portion  of  the 
bile  poured  into  the  intes- 
tine is  absorbed  either  as 
such  or  after  partial  decom- 
position, the  products  to  be 
used  in  some  way  in  the 
economy  and  presumably  in 
the  construction  of  bile  by 
the  liver.  There  are  many 
facts,  including  some  patho- 
logical phenomena,  that 
point  clearly  to  the  forma- 
tion of  the  pigments  of  bile 
from  hemoglobin  in  some 
of  its  stages  of  degeneration^ 

flttotogiaat^When  the  liver  fails  to  act  either  from  de- 


rm. m.-FartioB  oC  tHHwrene  MeUMtvr  ItepiUlo 
lomde  or  rMMti  mainUIeil  400  diMuaten 


t,  0,  g,  wpmM/  Vi&^Mto!?  I, 


Mood- 

{.UTMMselta.' 


iimmm 


iMmm 


BBJtaiii^wiWwiwg 


fift 


fi4.- 


8S9 


ANIMAL  PHYSIOLOOT. 


rangement  of  its  cells  primarily  or  owing  to  obstruction  to  the 
outflow  of  bile  leading  to  reabsorption  by  the  liver,  bile  acids 
land  bile  pigments  appear  in  the  urine  or  may  stain  the  tissues, 
(indicating  their  presence  in  excess  in  the  blood. 

"yThis  action  of  one  gland  (kidneys)  foriiiother  is  highly 
suggestive,  and  specially  important  io  bear  in  mind  in  medical 
practice,  both  in  treatment  and  prognosis.  The  chances  of  re- 
covery when  only  one  excreting  gland  is  diseased  are  much 
greater  evidently  than  when  several  are  involved.  Such  facts 
as  we  have  cited  show,  moreover,  that  there  are  certain  common 
fundamental  principles  underlying  secretion  everywhere — a 
statement  which  will  be  soon  more  fully  illioatrated. 


The  Natubb  or  thb  Act  of  Sbobbtion. 

We  are  now  about  ^to  consider  some  investigations,  more 
particularly  their  results,  which  are  of  extraordinary  interest. 

The  secreting  cells  of  the  salivary,  the  pancreatic  glands, 
and  the  stomach  have  been  studied  by  a  combination  of  histo- 
logical and,  more  strictly,  physiological  methods,  to  which  we 
shall  now  refer.  Specimens  of  iihese  glands,  both  before  and 
after  prolonged  secretion,  under  stimulation  of  these  nerves, 
were  hardened,  stained,  and  sections  prepared.  As  was  to  be 
expected,  the  results  were  not  entirely  satisfactory  under  these 
methods;  however,  the  pancreas  of  a  living  rabbit  has  been 
viewed  with  the  microscope  in  its  natural  condition;  and  by 
this  plan,  especially  when  supplemented  by  the  more  involved 
and  artificial  i^ethod  first  referred  to,  results  have  been  reached 


rm.  W7.— Portion  of  pawcrwit  ot  rabbit  (aft*  KMme  Md  L»).   A  rapicMnta  (laiid  at  rMrt ; 

B,d«ria«i "— 


which  may  be  ranked  among  the  greatest  triumphs  of  modem 
physiology. 


-m 


DIGESTION  OF  FOOD. 


887 


"uction  to  the 
rer,  bile  acids 
n  the  tissues, 

ler  is  highly 
nd  in  medical 
shances  of  re- 
ed are  much 
Such  facts 
rtain  common 
erywhere — a 
id. 

ION. 

g;ations,  more 
lary  interest, 
reatic  glands, 
ktion  of  histo- 
i,  to  which  we 
th  before  and 
these  nerves. 
As  was  to  be 
ry  under  these 
bbit  has  been 
ition;  and  by 
more  involved 
e  been  reached 


naMta^uidatrwt; 

phs  of  modem 


(^me  of  these  we  now  proceed  to  state  briefly.  To  begin 
with  the  pancreas,  it  has  been  shown  that,  when  the  gland  is 
not  secreting — i.  e.,  not  discharging  its  prepared  fluid — or  dur- 
ing the  so-called  resting  stage,  the  appearances  are  strikingly 
different  from  what  they  are  during  activity.  The  cell  pre- 
sents during  rest  an  inner  granular  zone  and  an  outer  clearer 
zone,  which  stains  more  readily,  and  is  relatively  small  in  size. 
The  lumen  of  the  alveolus  is  almost  obliterated,  and  the  in- 
dividual cells  very  indistinct.  After  a  period  of  secreting 
activity,  the  lumen  is  easily  perceived,  the  granules  have  dis- 
appeared in  great  part,  the  cells  as  a  whole  are  smaller,  and 
have  a  clear  appearance  throughout.  Coincident  with  the 
changes  in  the  gland's  cells  it  is  to  be  noticed  that  more  blood 
passes  through  it,  owing  to  dilatation  of  the  arterioles. 


Fio.  878.— SMtton  of  muoous  gUnd  («(t«r  Lftvdowiky).    In  A,  gtand  at  nat ;  In  B,  after 

McntliiK  Bk  WNiie  noM. 

Again,  the  course  of  the  changes  in  the  salivary  glands, 
whether  of  the  mucous  or  serous  variety,  is  very  similar.  In 
the  mucous  gland  in  the  resting  stage  the  cells  are  large,  and 
hold  much  clear  matter  in  the  interspaces  of  the  cell  network ; 
and,  as  this  does  not  stain  readily,  it  can  not  be  ordinary 
protoplasm.  This,  when  the  gland  is  stimulated  through  its 
nerves,  disappears,  leaving  the  containing  cells  smaller.  It 
,  has  become  mucin,  and  may  itself  be  called  mucinogen. 

It  is  to  be  noted  that,  as  the  cells  become  more  protoplasmic, 
less  burdened  with  the  products  of  their  activity,  the  nucleus 
becomes  more  prominent,  suggestive  of  its  having  a  probable 
directive  influence  over  these  manufacturing  processes. 

Substantially  the  same  chain  of  events  has  been  established 
for  the  serous  salivary  glands  and  the  stomach,  so  that  we 
may  safely  generalize  upon  these  well-established  facts. 


. 


,: 


I 


mfOKitm 


msHat.  -tsmmeemm 


(ii>iiiiiiii>iw«iwaMMiaaMBaB!!a 


898 


ANIIIAL  PHTS10L06T. 


It  seems  clear  that  a  series  of  changes  constructive  and,  from 
one  point  of  view,  destructive,  following  the  former  are  con- 


ria.an>.-Cluuigeatii 

B,  atteriiiodera£i9,  C  after 

stantly  going  on  in  the  glands  of  the  digestive  organ&  Proto- 
plasm under  nerve  influence  constructs  a  certain  substance, 
which  is  r^n  antecedent  of  the  final  product,  which  we  term  a 
ferment,  ic  is  now  customary  to  speak  of  these  changes  as 
constructive  (anabolic)  and  destructive  (katabolic),  though  we 
have  already  pointed  out  (page  270)  that  this  view  is,  at  best, 
only  one  way  of  looking  at  the  matter,  and  we  doubt  if  it  may 
not  be  cramping  and  misleading. 

.  ^We  must  also  urge  caution  in  regard  to  the  conception  to 
be  associated  with  the  use  of  the  terms  '*  resting  "  and  "  active  '* 
stage.  It  is  not  to  be  forgotten  that  strictly  in  living  cells 
there  is  no  absolute  rest— such  means  death ;  but,  if  these  terms 
be  understood  as  denoting  but  degrees  of  activity,  they  need 
not  mislead.  It  is  also  more  than  probable  that  in  certain  of 
the  glands,  or  in  some  animals,  the  processes  go  on  simultane- 
ously:  the  protoplasm  being  renewed,  the  zymogen,  or  mother- 
ferment,  being  formed,  and  the  latter  converted  into  actual  fer- 
ment, all  at  the  same  time. 

It  has  been  pointed  out  that  chorda  saliva  is  usually  more 
watery  than  t|iat  secreted  under  stimulation  of  the  sympathetic. 
When  atrcpine  is  injected  there  is  no  discharge  whatever,  not- 
withstanding that  the  usual  vascular  dilatation  follows,  from 
which  it  is  clear  that  the  water  is  actually  secreted. 

®ie  nature  of  secretion  is  now  tolerably  dear  ag  a  whole;, 
though  it  is  to  be  remembered  that  this  account  is  but  general, 
and  that  there  are  many  minor  difFerenoes  for  each  gland  and 
variations  that  can  scarcely  be  doaominated  minor  for  different 
animals.  Evidently  no  theory  of  filtration,  no  process  depend- 
ing solely  on  blood-pressure,  will  apply  here.  And  if  in  this, 
the  best-studied  case,  mechanical  theories  of  vital  processes 
utterly  fail,  why  attempt  to  fasten  them  upon  other  glands,  as 


tmmmffMi^iim^- 


ve  and,  from 
ner  are  con- 


f).  A.  dnrinK  'Mtj 
■gmmnwrtn 


l^ns.  Proto- 
n  substance^ 
:li  we  term  a 
3  changes  as 
i),  though  we 
w  is,  at  best, 
ibt  if  it  may 

K)nception  to 
Emd  "active" 
I  living  cells 
if  these  terms 
ity,  they  need 
in  certain  of 
m  simultane- 
n,  or  mother* 
ito  actual  fer- 

uBually  more 
I  sympathetic, 
rlwtever,  not- 
f ollows,  frcmi 
1 

raK  a  whole;. 
B  but  general, 
ioh  gland  and 
r  for  different 
ocess  depend- 
nd  if  in  this, 
ital  processes 
tier  glands,  as 


DIGESTION  OF  FOOD. 


829 


the  kidneys  and  the  lungs,  or,  indeed,  apply  such  crude  concep- 
tions to  the  subtle  processes  of  living  protoplasm  anywhere  or 
in  any  form  P 

It  is  somewhat  remarkable  that  an  extract  of  a  perfectly 
fresh  pancreas  is  not  proteolytic ;  yet  the  gland  yields  such  an 
extract  when  it  has  stood  some  hours  or  been  treated  with  a 
weak  acid.  These  facts,  together  with  the  microscopic  appear- 
ances, suggested  that  there  is  formed  a  forerunner^ to  the  actual 
ferment — a  zymogen,  or  mother-ferment,  which  at  the  mbment 
of  discharge  of  the  completed  secretion  is  converted  into  the 
actual  ferment.  We  might,  therefore,  speak  of  a  pepsinogen, 
typsinogen,  etc.,  and,  though  there  may  be  a  cessation  in  the 
series  of  processes,  and  no  doubt  there  is  in  some  animals,  this 
may  not  be  the  case  in  all  or  in  all  glands. 

BMNtiaa  I17  fhs  BtoouMh.— The  glands  of  the  stomach  differ 
in  most  animals  in  the  cardiac  and  pyloric  regions.  In  those 
of  the  former  sone,  both  cent.  jJ,  columnar,  aiid  parietal  (ovoid) 
cells  are  to  be  recognized.  It  was  thought  that  possibly  the 
latter  were  concerned  in  the  secretion  of  the  acid  of  the 
stomach,  but  this  is  by  no  means  certain.  Possibly  these,  like 
the  demilune  cells  of  the  pancreas,  may  be  the  progenitors  of 
the  central  (chief)  cells.  The  latter  certainly  secrete  ;:;'ep8in, 
and  probably  also  rennet.  Mucus  is  secreted  by  the  cells  lining 
the  neck  of  glands  and  covering  the  mucous  membrane  inter- 
vening between  their  moutha  The  production  of  hydrochloric 
acid  by  any  act  of  secretion  is  not  beUeved  in  by  all  writers, 
some  holding  that  it  is  derived  from  decomposition  of  sodium 
chloride,  possibly  by  lactic  acid.  So  simple  an  origin  is  not 
probable,  not  being  in  keeping  with  what  we  know  of  chemical 
processes  within  the  animal  body. 

MfrlMgMfein  of  ths  IMgtittv*  Oifaai.— -It  has  been  found,  both 
in  man  and  other  mammals,  that  when  death  follows  in  a 
healthy  subject  while  gastric  digestion  is  in  active  progress 
and  the  body  is  kept  warm,  a  part  of  the  stomach  itself  and 
often  adjacent  organs  are  digested,  and  the  question  is  con- 
stantly being  TaJsedjQlVhy  downoi  the  stCTmachjigest  itself 
during, life?  To  this  it  has  teen  answored^hat  the  gastric 
jmoe  iiToonstantly  being  neutralised  by  the  alkaline  blood ; 
and,  again,  that  the  very  vitality  of  a  tissue  gives  it  the  neces- 
sary resisting  powers,  a  view  contradicted  by  an  experiment 
which  is  conclusive.  If  the  legs  of  a  living  frog  be  allowed  to 
hang  against  the  inner  walls  of  the  stomach  of  a  mammal 
when  gastric  digestion  is  going  on,  they  will  be  digested. 


^4ii^^^^'-!2-''ri''ri0-ih.iitK^y}h:'r^f'JI»^^ 


,ijusii,yw!i»jwi*»,»' 


380 


ANIMAL  PHYSIOLOGY. 


The  first  view  (the  alkalinity  of  the  blood)  would  not  suffice 
to  explain  why  the  pancreas,  the  secretion  of  which  acts  beet 
in  an  alkaline  medium,  should  not  be  digested. 

^t  seems  to  us  there  is  a  good  deal  of  misconception  about 
the  facts  of  the  case.  Observation  on  St.  Martin  shows  that 
the  secretion  of  gastric  juice  runs  parallel  with  the  need  of  it, 
as  dependent  on  the  introduction  of  food,  its  quantity,  quality, 
etc.*  Now,  there  can  be  little  doubt  that,  if  the  stomach  were 
abundantly  bathed  when  empty  with  a  large  quantity  of  its 
own  acid  secretion,  it  would  suffer  to  some  extent  at  least. 
But  this  is  never  the  case ;  the  juice  is  carried  off  and  mixed 
with  the  food.  This  food  is  in  constant  motion  and  doubtless 
the  inner  portions  of  the  cells,  which  may  be  regarded  as  the 
discharging  region,  while  the  outer  (next  the  blood  capillaries, 
the  chief  manufacturing  region  of  the  digestive  ferment)  are 
frequently  renewed. 

Such  considerations,  though  they  seem  to  have  been  some- 
what left  out  of  the  case,  do  not  go  to  the  bottom  of  the 
matter.  Amoeba  and  kindred  organisms  do  not  digest  them- 
selves. Some  believe  that  the  little  pulsatile  vacuoles  of  the 
Inf usorians  are  a  sort  of  temporary  digestive  cavities. 

I^But,  to  one  who  sees  in  the  light  of  evolution,  it  must  be 

clear  that  a  structure  could  not  have  been  evolved  that  would 
bejelf -destructive. 

The  difficulty  here  is  that  which  lies  at  the  very  basis  of  all 
life.  We  might  ask.  Why  do  living  things  live,  since  they  are 
constantly  threatened  with  destruction  from  within  as  from 
without  ?  Whyjdo  not  tibLeJlYer^  kidney,  a;nd  other  glands^that 
secrete  noxious  substancee^  poison  themsels^  We  can  not 
in~defail  explain  these  things ;  but  we  wish  to  make  it  clear 
that  the  difficulty  as  regards  the  stomach  is  not  peculiar  to 
that  gland,  and  that  even  from  the  ordinary  point  of  view  it 
has  been  exaggerated.  , 

OompantiTe. — More  careful  examination  of  the  stomachs  of 
some  mammals  has  revealed  the  fact  that  in  several  animals, 
in  which  the  stomach  appears  to  be  simple,  it  is  in  reality 
compound.  There  are  different  grades,  however,  which  may 
be  regarded  as  transition  forms  between  the  true  simple 
stomach  and  that  highly  compound  form  of  the  organ  met 
with  in  the  ruminants. 

It  has  been  shown  recently  that  the  stomach  of  the  hog  has 
an  oesophageal  dilatation;  aud  that  the  entire  organ  may  be 
divided  into  several  sones  with  different  kinds  of  glandular 


idviriniiiiaui 


881 


Id  not  suffloe 
ch  acts  beet 

jption  about 
shows  that 
16  need  of  it, 
bity,  quality, 
bomach  were 
uitity  of  its 
ent  at  least. 
E  and  mixed 
nd  doubtless 
arded  as  the 
d  capillaries, 
ferment)  are 

e  been  some- 

tttom  of  Hbe 

digest  them- 

cuoles  of  the 

dies. 

1,  it  must  be 

d  that  would 

y  basis  of  all 
ince  they  are 
bhin  as  from 
tr  glands  that 
"We'can  not 
nake  it  clear 
)t  peculiar  to 
int  of  view  it 

e  stomachs  of 
eral  animals, 

is  in  reality 
r,  which  may 

true  simple 
le  organ  met 

if  the  hog  has 

irgan  may  be 

of  glandular 


Fm.  no:-Iirterlar  of  bone'sitainiidi 
(after  CbMnrem). ,  A,  toft  ■•o ;  B, 
right  mm;  C, dnodHua dllatatloiL 


DIGESTION  OF  FOOD. 


epithelium,  etc.  These  portions  differ  in  digestive  power,  in 
the  characteristics  of  the  fluid  secreted,  and  other  details  be- 
yond those  which  a  superficial  examination  of  this  organ 
would  lead  one  to  suspect. 

The  stomach  of  the  horse  represents  a  more  advanced  form 
of  compound  stomach  than  that  of  the  hog,  which  is  not  evi- 
dent, however,  until  its  glandular 
structure  is  examined  closely.    The 
entire  left  portion  of  the  stomach 
represents  an  oesophageal   dilata- 
tion lined  with  an  epithelium  that 
closely  resembles  that  of  the  oesoph- 
agus, and  with  little  if  any  digest- 
ive function.    It  thus  appears  that 
the  stomach  of  the  horse  is  in  reali- 
ty smaller,  as  a  true  digestive  gland, 
than  it  seems,  so  that  a  great  part 
of  the  work  of  digestion  must  be 
done  in  the  intestine;  though  in 
this  animal,  if  the  food  be  retained 
long  as  it  is  in  the  hog,  which  is 
not,  however,  the  general  opinion  as  regards  the  stomach  of  the 
horse,  salivary  digestion  may  continue  for  a  considerable  period 
after  the  food  has  left  the  mouth.    The  secretion  of  mucus  by 
the  stomach  in  herbivora  is  abundant. 

The  Movements  of  the  Digestive  Organs.*^ 

As  with  other  parts  of  the  body,  so  in  the  alimentary  tract, 
the  slower  kind  of  movement  is  carried  out  by  plain  muscu- 
lar fibers ;  and  the  movements,  as  a  whole,  belong  to  the  class 
known  as  peristaltic ;  in  fact,  it  is  only  at  the  beginning  of  the 
digestive  tract  that  voluntary  (striped)  muscle  is  to  be  found 
and  to  a  limited  extent  in  the  part  next  to  this— i.  e.,  in  the 
oesophagus. 

Teeth  in  the  highly  organized  mammal  are  remarkable  in 
being  to  the  least  degree  living  struotares  of  any  in  the  entire 
Mumal,  thus  being  in  marked  contrast  to  other  organs.  The 
enamel  covering  their  exposed  surfaces  is  the  hardest  of  all  the 
tissues  and  is  necessarily  of  low  vitality.  We  have  already 
alluded  to  the  difference  in  the  teeth  of  different  animals,  and 
their  relation  to  customary  food  and  digestive  functions.  In 
fact,  it  is  dear  that  the  teeth  and  all  the  parts  of  the  digestive 


.W«t»miM)IIWW*l»ii'IMBi<W-l"Wi 


wmnii^wiiWi 


833 


ANIMAL  PHTSIOLOGT. 


system  are  correlated  to  one  another.  The  compound  stomach 
of  the  ruminants,  with  its  slow  digestion  of  a  bulky  mass  of 
food,  which  must  be  softened  and  thoroughly  masticated  be- 
fore the  digestive  juices  can  attack  it  successfully,  harmonises 
with  the  powerful  jaws,  strong  muscles  of  mastication,  and 
grinding  teeth;  and  all  these  in  marked  contrast  with  the 
teeth  of  a  carnivorous  animal  with  its  simple  but  highly  effect- 
ive stomach.    Compare  figures  in  earlier  pages. 

Mastication  in  man  is  of  that  intermediate  character  befit- 
ting  an  omnivorous  animal.  The  jaws  have  a  lateral  and 
forward-and-backward  movement,  as  well  as  a  vertical  one, 
ihough  the  latter  is  predominant.  The  upper  jaw  is  like  a 
fixed  millstone,  against  which  the  lower  jaw  works  as  a  nether 
millstone.  The  elevation  of  the  jaw  is  effected  by  the  mas- 
seter,  temporal,  and  internal  pterygoid  muscles ;  depressed  by 
the  mylohyoid  and  geniohyoid,  though  principally  by  the  di- 
gastric. The  jaw  is  advanced  by  the  external  pterygoids; 
unilateral  contraction  of  these  muscles  also  produces  lateral 
movement  of  the  inferior  maxilla,  which  is  retracted  by  the 
more  horizontal  fibers  of  the  tempond. 

The  cheeks  and  tongue  likewise  take  part  in  preparing  the 
food  for  the  work  of  the  stomach,  nor  must  the  lips  be  over- 
looked even  in  man.  The  importance  of  these  parts  is  well 
illustrated  by  the  imperfect  mastication,  etc.,  when  there  is 
paralysis  of  the  muscles  of  which  they  are  formed.  Even  when 
there  is  loss  of  sensation  only,  the  work  of  the  mouth  is  done 
in  a  clumsy  way,  showing  the  importance  of  common  sensation, 
as  well  as  the  muscular  sense. 

Vanrou  9mgfij. — ^The  muscles  of  the  ton  ^ue  are  governed  by 
the  hypoglossal  nerve;  the  other  muscles  of  mastication  chiefly 
by  the  fifth.  The  afferent  nerves  are  branches  of  the  fifth  and 
glosso-pharyngeal.  It  is,  of  course,  important  that  the  food 
should  be  rolled  about  and  thoroughly  mixed  with  saliva  (in- 
salivation). 

Deglutitioit— The  transportation  of  the  food  from  the  mouth 
to  the  stomach  involves  a  series  of  co-ordinated  musotilar  acts 
of  a  complicated  character,  by  which  difficulties  are  overcome 
with  marvelous  success. 

It  will  be  remembered  that  the  respiratory  and  digestive 
tracts  are  both  developed  from  a  common  simple  tube — a  fact 
which  makes  the  close  anatomical  relation  between  these  two 
physiologically  distinct  systems  intelligible ;  but  it  also  involves 
difficulties  and  dangers.    It  is  well  known  that  a  small  quantity 


iWlinllMi 


1 


DIGESTION  OF  POOD. 


888 


nd  stomacli 
ky  mass  of 
iticated  be- 
hannonises 
cation,  and 
it  with  the 
ighly  effect- 

racter  befit- 
lateral  and 
''ertical  one, 
w  is  like  a 
I  as  a  nether 
yy  the  mas- 
iepressed  by 
y  by  the  di- 
pterygoids; 
luces  hiteral 
icted  by  the 

reparing  the 
iips  beover- 
larts  is  well 
len  there  is 
Even  when 
»uth  is  done 
on  sensation, 

governed  by 
lation  chiefly 
the  fifth  and 
lat  the  food 
h  saliva  (in- 

m  the  mouth 
Lusoular  acts 
ire  overcome 

nd  digestive 
tube — a  fact 
m  these  two 
also  involves 
oall  quantity 


of  food  or  drink  entering  the  windpipe  produces  a  perfect 
storm  of  excitement  in  the  respiratory  system.   The  food,  there- 


in. «.-0»vitiM  of  BMOtti  Md  pbwraEjjte.  (^«r  "?W^  *jittoi»jto  mjdiM  to^  oT 
ftwe  Mid  •BpMTlor  iKirtloo  Jilne«di,  Adgwd  to  Aow  tto  B^^ 

SwuJm of  hyoIdbS* ;  n. tayiiiwa portli» of  oatlly of  phiq^ 

fore,  when  it  reaches  the  oesophagus,  must  be  kept,  on  the  one 
hand,  from  entering  the  nasal,  and,  on  the  other,  the  laryngeal 
openings.  This  is  accomplished  as  follows :  When  the  food  has 
been  gathered  into  a  bolus  on  th<9  back  of  the  tongue,  the  tip  of 
this  organ  is  pressed  against  the  hard  palate,  by  which  the 
mass  is  prevented  from  passing  forwardi  and,  at  the  same  time, 
forced  back  into  the  pharynx,  the  soft  palate  being  raised  and 
the  edges  of  the  pillars  of  the  fauces  made  to  approach  the 
uvula,  which  fills  up  the  gap  remaining,  so  that  the  posterior 
nares  are  closed  and  an  inclined  plane  provided,  over  which 
the  morsel  glides.  The  after-result  is  said  to  depend  on  the 
size  of  the  bolus.    When  considerable,  the  constrictors  of  the 


384 


ANIMAL  P  :  .    iOLOOY. 


pharynx  seize  it  and  press  it «'  ^  '•.*  vue  gallot ;  when  the  mor- 
sel is  small  or  liquid  is  8wall.>.(red,  it  is  rapidly  propelled  on- 
ward by  the  tongfue,  the  oesophagus  and  ^sharynx  being  largely 
passive  at  the  time,  though  contracting  slowly  afterward ;  at 
the  same  time  the  larynx  as  a  whole  is  raised,  the  epiglottis 
pressed  down,'  chiefly  by  the  meeting  of  the  tongue  and  itself, 
while  its  cushion  lies  oVer  the  rima  gltMidis,  which  is  closed  or 
all  but  closed  by  the  action  of  the  sphincter  muscles  of  the 
larynx,  so  that  the  food  passes  over  and  by  this  avenue  of  life, 
not  only  closed  but  covered  by  the  glottic  lid.  The  latter  is 
not  so  essential  as  might  be  supposed,  for  persons  in  whom  it 
was  absent  have  been  known  to  swallow  fairly  well.  The 
ascent  of  the  larynx  any  one  may  feel  for  himself ;  and  the  be- 
havior of  the  pharynx  and  larynx,  especially  the  latter,  may 
he  viewed  by  the  laryngoscope.  The  grip  of  the  pharyngeal 
muscles  and  the  oesophagus  may  be  made  clear  by  attaching  a 
piece  of  food  (meat)  to  a  string  and  allowing  it  to  be  partially 
swallowed. 

The  upward  movement  of  food  under  the  action  of  the  con- 
strictors of  the  pharynx  is  anticipated  by  the  closure  of  the 
passage  by  the  palato-glossi  of  the  anterior  pillars  of  the  fauces. 

The  circular  muscular  fibers  of  the  gullet  are  probably  the 
most  important  in  squeezing  on  the  food  by  a  peristaltic  move- 
ment, passing  progressively  over  the  whole  tube,  though  the 
longitudinal  also  take  part  in  swallowing,  perhaps,  by  steady- 
ing the  organ. 

Swallowing  will  take  place  in  an  animal  so  long  as  the 
medulla  oblongata  remains  intact ;  and  the  center  seems  to  lie 
higher  than  that  for  respiration,  as  the  latter  act  is  possible 
when,  from  slicing  away  the  medulla,  the  former  is  not.  An- 
encephalous  monsters  lacking  the  cerebrum  can  swallow,  suck, 
and  breathe. 

Food  placed  in  the  pharynx  of  animals  when  unconscious 
is  swallowed,  proving  that  volition  is  not  essential  to  the  act; 
but  our  own  consciousness  dedlares  that  the  first  stage,  or  the 
removal  of  the  food  from  the  mouth  to  the  pharynx,i8  volun- 
tary. 

When  we  seem  to  swallow  voluntarily  there  is  in  reality  a 
stimulus  applied  to  the  fauces,  in  the  absence  t>f  food  and  drink, 
either  by  the  back  of  the  tongue  or  by  a  little  .^iva. 

It  thus  appears  that  deglutition  is  an  act  in  the  main  reflex, 
though  initiated  by  volition.  The  afferent  nerves  concerned 
are  usually  the  glosso-pharyngeal,  some  branches  of  the  fifth. 


UMiltrifB-rr-T'^"-^^"''''^ 


DIOESTION  OF  FOOD. 


885 


en  the  mor- 
"opelled  on- 
aing  largely 
terward;  at 
le  epiglottis 
Band  itself, 
is  closed  or 
Bcles  of  the 
9nue  of  life, 
he  latter  is 
in  whom  it 
well.  The 
and  the  be- 
latter,  may 
pharyngeal 
attaching  a 
be  partially 

L  of  the  con- 
>sure  of  the 
f  the  fauces. 
>robably  the 
italtic  move- 
,  though  the 
B,  by  steady- 
long  as  the 
seems  to  lie 
b  is  possible 
is  not.  An- 
rallow,  suck, 

unconscious 
[to  the  act; 
stage,  or  the 
ax,'is  volun- 

in  reality  a 
d  and  drink, 
a. 

main  reflex, 
IS  concerned 
of  the  fifth. 


and  of  the  vagus.  The  efferent  nerves  are  those  uf  the  numer- 
ous muscles  concerned. 

When  food  has  reached  the  gullet,  it  is,  of  course,  no  longer 
under  the  control  of  the  will. 

Section  of  the  vagus  or  stimulation  of  this  nerve  modifies 
the  action  of  the  oesophagus,  though  it  is  known  that  contrac- 
tions may  be  excited  in  the  excised  organ ;  but  no  doubt  nor- 
mally the  movements  of  the  gullet  arise  in  response  to  natural 
nerve  stimulation. 

OompantiT*. — That  swallowing  is  independent  of  gravity  is 
evident  from  the  fact  that  long-necked  animals  (horse,  giraffe) 
can  and  do  usually  swallow  with  the  head  and  neck  down,  so 
that  the  fluid  is  rolled  up  an  inclined  plane.  The  peristaltic 
nature  of  the  contractions  of  the  gullet  can  also  be  well  seen 
in  such  animals.  In  the  frog  the  gullet,  as  well  as  the  mouth, 
is  lined  with  ciliated  epithelium,  so  that  in  a  recently  killed 
animal  one  may  watch  a  slice  of  moistened  cork  disappear  from 
the  mouth,  to  be  fgund  shortly  afterward  in  the  stomach.  The 
rate  of  the  descent  is  surprising — in  fact,  the  movement  is 
plainly  visible  to  the  unaided  eye. 

TIm  MofOBMito  of  the  ItoimMh.— The  stomach  of  mammals, 
including  man,  is  provided  with  three  layers  of  muscular  fibers : 
1.  External  longitudinal,  a  continuation  of  those  of  the  oesopha- 
gus.   2.  Middle  circular.    #3.  Internal  oblique.    The  latter  are 


i 


Fia.  ML— HnmMi  itonwcii  (after  Sappey).  1.  osMphagiM :  »,  cinNilar  flben  at  oeaqpbaseal 
openlnc;  8, 8,  drcnlar  flben  at  leiaer  cnrratiire ;  4, 4,  circular  flben  at  the  pylorus  ;&,  6. 
«,  7, 8,  oblique  flben ;  9, 10,  flben  of  thi*  layer  oorerinc  the  gratter  pouch ;  n.porttDnot 
■tomach  from  which  theae  flben  have  been  remoTed  to  ihow  the  aubJiMwnt  circular  flbers, 


836 


ANIMAL  PHTSIOLOOT. 


i 


the  least  perfect,  viewed  as  an  investing  coat.  The  pyloric  end 
of  the  stomach  is  best  supplied  with  muscles ;  where  also  there 
is  a  thick  muscular  ring  or  sphincter,  as  compared  with  which 
the  cardiac  sphincter  is  weak  and  ill-developed. 

The  movements  of  the  stomach  begin  shortly  after  a  meal 
has  been  taken,  and,  as  shown  by  observations  on  St.  Martin, 
continue  for  houm,  not  constantly,  but  periodically.  The  effect 
of  the  conjoint  action  of  the  different  sets  of  muscular  fibers  is 
to  move  the  food  from  the  cardiac  toward  the  pyloric  end  of 
the  stomach,  along  the  greater  curvature  and  back  by  the  lesser 
curvature,  while  there  is  also,  probably,  a  series  of  in-and-out 
currents  to  and  from  the  center  of  the  food-mass.  The  quantity 
of  food  is  constantly  being  lessened  by  the  removal  of  digested 
portions,  either  by  the  blood-vessels  of  the  organ  or  by  its 
passing  through  the  pyloric  sphincter.  The  empty  stomach  is 
quiescent  and  contracted,  its  mucous  membruie  being  thrown 
into  folds. 

The  movements  of  the  stomach  may  be  regarded  as  reflex, 
the  presence  of  food  being  an  exciting  cause,  though  probably 
not  the  only  one ;  and  so  largely  automatic  is  the  central  mech- 
anism concerned,  that  but  a  feeble  stimulus  suffices  to  arouse 
them,  espeokiliy  at  the  accustomed  time. 

Of  the  paths  of  the  impulses,  either  afferent  or  efferent, 
little  is  known.  Certain  effects  follow  section  or  stimulation  of 
the  vagi  or  splanchnics,  but  these  can  not  be  predicted  with 
certainty,  or  the  exact  relation  of  events  indicated. 

CB  is  said  that  the  movements  of  the  stomach  cease,  even 
when  it  is  full,  during  sleep,  from  which  it  is  argued  that  gas- 
tric movements  do  normally  depend  on  the  influence  of  the 
nervous  system.  However,  the  subject  is  too  obRcure  at  pres- 
ent for  further  discussion. 

Comiuititii^— Recent  investig^tiooB  on  the  stomach  of  the 
pig  indicate  that  in  this  animal  the  omitents  of  the  two  aids  of 
the  stomach  may  long  remain  but  little  mingled;  imd  eaob  is 
certainly  the  casein  this  organ  among  ruminants. 

P»thokgiaal.-^8tention  of  the  stomach,  eitiier  jfrom  excess 
of  food  or  gas  arising  from  fermentative  chuiges,  or  by  secre- 
tion from  the  blood,  may  cauw,  by  upward  presmire  on  the 
diaphragm,  etc.,  uneasiness  from  hunpwed  respiration,  and  ir- 
regularity of  the  heart,  possibly,  also,  in  part  traceable  to  the 
physical  interference  with  its  movements.  After  great  and 
prolonged  distention  there  niay  be  weakened  digestion  for  a 
considerable  interval.    It  seems  not  improbable  that  this  is  to 


tumtm 


mmmmm 


iiiuci'.'iSMSVcviM&it'V-' 


3  pyloric  *nd 
re  also  there 
i  with  which 

after  a  meal 
1  St.  Martin, 
r.  The  effect 
ular  fibers  is 
rloric  end  of 
by  the  lesser 
>f  in-and-out 
rhe  quantity 
il  of  digested 
an  or  by  its 
;y  stomach  is 
mng  thrown 

ded  as  reflex, 
igh  probably 
ientral  mech- 
}es  to  arouse 

t  or  efferent, 
timulation  of 
■edicted  with 

h  cease,  even 
aed  that  gas- 
iuence  of  the 
cure  at  pr«9- 

)mach  of  the 
e  two  Olds  of 
;  imd  audi  is 

r  from  excess 
I,  or  by  secre- 
NNKire  on  the 
ation,  and  ir- 
iceable  to  the 
er  great  and 
gestion  for  » 
bat  this  is  to 


DIOBOTION  OF  FOOD. 


be  explained,  not  alone  by  the  impaired  elasticity  (Tiitality)  of 
the  muscular  tissue,  but  also  by  defective  secreting  power.  It 
is  not  necessary  to  impress  the  lesson  such  facts  oohvey. 

The  latMtiiial  ]bfaMBta.^The  circular  fibers  pli^  a  much 
more  important  part  than  the  longitudinal,  being,  in  fact^  much 
more  developed.  It  is  also  to  be  remembered  that  herves  in 
the  form  of  plexuses  (of  Auerbach  and  Meissner)  abound  in  its 
walls. 

Normally  the  movement,  slowly  progressive,  with  occasional 
baitings,  is  from  above  downward,  stopping  at  the  ileo-ceecal 
valve ;  the  movements  of  the  large  gut  being  apparently  mostly 
independent. 

Movements  may  be  excited  by  external  or  internal  stimula- 
tion, and  may  be  regarded  as  reflex ;  in  which,  however,  the 
tendency  for  the  central  cells  to  discharge  themselves  is  tio 
great  (automatic)  that  only  a  feeble  stimulus  is  required,  the 
normal  one  being  the  presence  of  food. 

It  is  noticeable  in  a  recently  killed  animal,  or  in  one  in  the 
last  stages  of  asphyxia,  tr^t  the  intestines  contract  vigorously. 
Whether  this  is  due  to  the  action  of  blood  overcharged  with 
carbonic  anhydride  and  deficient  in  oxygen  on  the  centers  pre- 
siding over  the  movements,  on  the  nerves  in  the  intestinal 
walls,  or  on  the  muscle-cells  directly,  is  not  wholly  clear,  but  it 
is  probable  that  all  of  these  may  enter  into  the  restllt.  The 
vagus  nerve,  when  stimulated,  gives  rise  to  movements  of  the 
intestines,  while  the  splanchnic  seems  to  have  the  reverse  effect ; 
but  the  cerebrum  itself  has  an  influence  over  the  movements  of 
the  gut,  as  is  plain  from  the  diarrhoea  traceable  to  unusual 
fear  or  anxiety.  There  is  little  to  add  in  regard  to  the  move- 
ments of  the  large  intestine.  They  are,  no  doubt,  of  consider- 
able importance  in  animals  in  which  it  is  extensive.  Normally 
they  begin  at  the  ileo-ceecal  valve. 

B«feaalim.-*-The  removal  of  the  waste  matter  from  the  ali- 
Tnentary  tract  is  a  complicated  process,  in  which  both  smooth 
andstriped  muscle,  the  spinal  cord,  and  the  brain  take  part. 

/ptefecation  may  take  place  during  the  unconsciousness  of 
sleep  or  of  disease,  and  so  be  wholly  indlependent  of  the  will ; 
but,  as  we  well  know,  this  is  not  usually  the  case.  Against  ac- 
cidental discharge  of  fsBces  there  is  a  provision  in  the  sphinc- 
ter ani,  the  tone  of  which  is  lost  when  the  lower  part  of  the 
spinal  cord  is  destroyed.  We  are  conscious  of  being  able,  by  an 
effort  of  will,  to  prevent  the  relaxation  of  the  sphincter  or  to 
increase  its  holding  power,  though  the  latter  is  probably  almost 


■iiati!.>#iii»,'  I'lwitiWHiiMii 


mmMmi 


ii*«nuii>mwuiB" 


888 


ANIMAL  PHTSIOLOOT. 


wholly  due  to  the  action  of  extrinsic  muscles ;  at  all  events  any 
one  may  convince  himself  that  the  latter  may  he  made  to  take 
a  great  part  in  preventing  f eooal  discharge,  though  whether  the 
tone  of  the  sphincter  can  be  increased  or  not  by  volition  it  is 
difficult  to  say. 

What  happens  during  an  ordinary  act  of  defecation  is  about 
as  follows :  After  a  long  inspiration  the  glottis  is  closed ;  the 
diaphragm,  which  has  descendea,  remains  low,  affording,  with 
the  obstructed  laryngeal  outlet,  a  firm  basis  of  support  for  the 
action  of  the  abdominal  muscles,  which,  bearing  on  tha  intes- 
tine, forces  on  their  contents,  which,  bef pre  the  act  has  been 
called  for,  have  been  lodged  mostly  in  the  large  intestine ;  at 
the  same  time  the  sphincter  ani  is  relaxed  and  peristaltic  move- 
ments accompany  and  in  some  instances  precede  the  action  of 
the  abdominal  muscles.  The  latter  may  contract  vigorously  on 
a  full  gut  without  success  in  the  absence  of  the  intestinal  peri- 
stalsis, as  too  many  cases  of  obstinate  constipation  bear  witness. 

like  deglutition,  and  unlike  vomiting,  there  is  usually  both 
a  voluntary  and  involuntary  part  to  the  act. 

Though  the  will,  through  the  cerebrum,  can  inhibit  defeca- 
tion, it  is  likely  that  it  does  so  through  the  influence  of  the 
cerebrum  on  some  center  in  the  cord ;  for  in  a  dog,  the  lumbar 
cord  of  which  has  been  divided  from  the  dorsal,  the  act  is,  like 
micturition,  erection  of  the  penis,  and  others  which  are  under  the 
control  of  the  will,  still  possible,  though,  of  course,  performed 
entirely  unconsciously. 

Vowiriiy. — If  we  consult  our  own  consciousness  and  observe 
to  the  best  of  our  ability,  supplementing  information  thus 
gained  by  observations  <m  others  and  on  the  lower  animals,  it 
will  becf)mfj  apx>arent  that  vomiting  implies  a  series  of  co-ordi- 
nated movements,  into  which  volition  does  not  enter  either 
necessarily  or  habitually.  There  is  usually  a  preceding  nausea, 
with  a  temporary  flow  of  saliva  to  excess.  The  act  is  initiated 
by  a  deep  inspiration,  followed  by  closure  of  the  glottis. 
Whether  the  glottis  is  closed  during  or  prior  to  the  entrance 
of  air  is  a  matter  of  disagreement.  At  all  events,  the  dia- 
phragm descends  and  remains  fixed,  the  lower  ribs  being  I'e- 
traoted.  The  abdominal  muscles  then  acting  against  this  sup- 
port, force  out  the  contents  of  the  stomach,  in  which  they  are 
assisted  by  ilie  essential  relaxation  of  the  cardiac  sphincter,  the 
s'Lortimmg  of  the  oesophagus  by  its  long^itudinal  fibers,  and  the 
extension  aud  straightening  of  the  neck,  together  with  the  open- 
ing of  the  mouth. 


illiilMi  i]l«»liii>i>— llii 


til  events  any 
onade  to  take 
1  whether  the 
volition  it  is 

ation  is  about 
is  closed;  the 
fording,  with 
ipport  for  the 
on  the  intes- 
act  has  been 
I  intestine;  at 
istaltic  move- 
the  action  of 
vigorously  on 
ntestinal  peri- 
1  bear  witness. 
i  usually  both 

nhibit  def  eoa- 
fluence  of  the 
ig,  the  lumbar 
the  act  is,  like 
I  are  under  the 
rse,  performed 

88  and  observe 
ormation  thus 
ver  animals,  it 
ries  of  co-ordi- 
>t  enter  either 
ceding  nausea, 
act  is  initiated 
)f  the  glottis. 
10  the  entrance 
rents,  the  dia- 

ribs  being  ve- 
(Mnst  this  sup- 
!^hich  they  are 
a  sphincter,  the 

fibers,  and  the 
r  with  the  open- 


DIOBSTION  OP  POOD, 


839 


As  the  expulsive  effort  takes  place,  it  is  accompanied  by  an 
expiratory  act  which  tends  to  keep  the  egesta  out  of  the  larynx 
«nd  carry  them  onward,  though  it  may  also  contrihute  to  over- 
come the  resistance  of  the  elevated  soft  palate,  which  serves  to 
protect  the  nasal  passages.  The  stomach  and  oesophagus  are 
not  wholly  passive,  though  their  part  is  not  so  important  in 
the  adult  as  might  be  inferred  from  observing  vomiting  in 
infants,  the  peristalsis  of  these  organs  apparency  sufficing  in 
them  to  empty  the  stomach. 

Retching  may  be  very  violent  and  yet  ineffectual  when  the 
cardiac  sphincter  is  not  fully  relaxed.  The  pyloric  outlet  is 
usually  closed,  though  in  severe  and  long-continued  vomiting 
bile  is  often  ejected,  which  must  have  reached  the  stomach 
through  the  pylorus. 

Gompantivs.— The  ease  with  which  some  animals  vomit  in 
comparison  with  others  is  extraordinary,  as  in  camivora  like 
our  dogs  and  cats ;  a  matter  of  importance  t6  an  animal  ac- 
customed in  the  wild  state  to  eat  entire  carcasses  of  animals — 
hair,  bones,  etc.,  included. 

The  readiness  with  which  an  animal  vomits  depends  in  great 
part  on  the  conformation  and  relations  of  the  parts  of  its  digest- 
ive tract. 

The  horse  vomits  with  difficulty— its  stomach  and  its  car- 
diac opening  being  small  and  peculiar  in  shape  (Figs.  261  and 
280),  while  its  cBSophagus  is  long.  The  stomach  of  the  htunan 
being  during  infantile  life  is  less  pouched  than  in  the  adult, 
which  in  part  explains  the  ease  with  which  infants  vomit. 

But  the  matter  is  complex;  much  depends  on  the  proper 
co-ordinations  being  made,  and,  this  being  well  or  ill  accom- 
plished, accounts  for  the  variations  in  the  ease  with  which  dif- 
ferent persons  vomit. 

Patliatotiflal.— Vomiting  may  arise  from  the  presence  of  renal 
or  biliury  calculi  (reflex  action) ;  from  disease  of  the  cerebrum 
or  the  medulla ;  from  obstruction  in  the  pyloric  region  or  in 
the  intestines ;  from  emotions ;  from  revived  unpleasant  men- 
tal dissociations;  from  nauseous  tastes,  etc.  It  may  be  qnes- 
tiohable  whether  some  of  these  are  properly  termed  "  patho- 
logical." 

Pyrosis  is  due  to  the  anti-peristaltic  action  of  the  stomach 
and  oesophagus  alone,  so  that  it  is  a  sort  of  partial  vomiting 
mad  allied  to  the  regurgitation  of  special  secretions,  as  from  the 
crops  of  pigeons,  or  of  food  from  the  stomachs  of  ruminants. 
We  have  known  oases  in  which  anti-peristalsis  was  conflndd  to 


'840 


ANIMAL  PHYSIOLOGY. 


the  pharynx  alone.  Some  persona  seem  to  have  acquired  the 
power  of  regurgitating  food  and  masticating  it  afresh. 

The  excessive  vomiting  following  ohstruction  of  the  howels 
is  comparahle  to  the  unusual  action  of  the  heart,  ureter,  blad- 
der, etc.,  when  there  is  hindrance  to  the  outflow.  As  we  have 
already  explained  for  the  heart,  we  regard  this  as  the  resump- 
tion of  a  power  of  independent  action  seen  in  ancestral  forms 
and  marked  when  the  nervous  system  is  no  longer  exercising 
its  usual  control  and  direction.  Not  that  this  or  similar  be- 
havior may  not  result  from  excessive  stimulation,  loading  to 
unusual  central  nervous  discharge,  but  it  certainly  does  happen 
independraitly  of  the  nervous  system,  and  may  be  witnessed  in 
the  hearts  of  cold-blooded  animals  when  all  their  nerves  are 
divided. 

Similarly,  the  habit  of  regurgitating  the  food  is  intelligible 
in  the  light  of  evolution.  The  fact  that  mammals  are  descended 
from  lower  forms  in  which  unstriped  muscle-cells  go  to  form 
organs  that  have  a  rhythmically  contractile  function,  renders 
it  clear  why  this  function  may  become,  as  in  ruminants,  spe- 
cialized in  certain  parts  of  the  digestive  tract ;  why  carnivora 
should  vomit  readily,  and  why  human  subjects  should  learn  to 
regurgitate  food.  Th«re  is,  so  to  speak,  a  latent  inherited  ca- 
pacity which  may  be  developed  into  actual  function.  Apart 
fi-om  this  it  is  difficult  to  understand  such  cases  at  all. 

The  vomiting  center  is  usually  located  in  the  medulla,  and 
is  represented  as  working  in  concert  with  the  respiratory  center. 
But  when  we  consider  that  there  is  usually  an  increased  flow 
of  saliva  and  other  phenomena  involving  additional  central 
nervous  influence,  we  see  reason  to  believe  in  co-ordinated 
action  implying  the  use  of  parts  of  the  central  nervous  System 
not  so  closely  connected  anatomically  as  the  respiratory  and 
vomiting  centers  are  assumed  to  be. 

Indeed,  as  we  before  indicated,  it  does  not  seem  probable 
that  the  doctrin..  of  centers  in  its  present  form,  especially  with 
such  precise  limitations,  both  anatomically  and  physiologically, 
will  continue  to  be  maintained.  We  seem  to  hav«  been  over- 
looking the  connection  of  parts  while  occupied  with  defining 
their  limits.  It  is  not,  however,  yec  possible  to  substitute 
other  explanations  that  shall  be  wholly  satisfactory ;  and  we 
make  these  remarks  to  keep  the  student  expectant  of  progress, 
for,  as  a  distinguished  exponent  of  »  ence  has  said,  "  When 
VScienct  adopts  a  [rigid]  creed^she  commits  suicidey 

We  do  no+  know  thi$  part  ta^n,  if  anyTl^TEe  splanchnic 


acquired  the 
resh. 

[)f  the  howelfl 
ureter,  blad- 
As  we  have 
I  the  resump- 
cestral  forms 
;er  exercising 
r  similar  be- 
>n,  loading  to 
J  does  happen 
)  witnessed  in 
ir  nerves  are 

is  intelligible 
are  descended 
Us  go  to  form 
Lction,  renders 
iminants,  spe- 
vhy  carnivora 
hould  learn  to 

I  inherited  ca- 
iction.  Apart 
it  all. 

)  medulla,  and 
dratory  center, 
increased  flow 
itional  central 

II  co-ordinated 
lervous  System 
sspiratory  and 

seem  probable 
especially  with 
)hysiologically, 
lave  been  over- 
[  vdth  defining 
»  to  substitute 
ictory;  and  we 
mt  of  progress, 
8  said,  "\nien 
ide^J 
The  splanchnic 


'  -irnipiwiilMillBl*' 


DIGESTION  OF  FOOD. 


Ml 


or  other  nervee  of  the  sympathetic  system ;  but,  f roin  the  fact 
that  discharge  of  the  gastric  contents  is  impossible  when  the 
vagi  are  cut,  it  is  likely  that  the  efferent  impulses,  determining 
the  relaxation  of  the  cardiac  sphincter,  descend  by  these  nerves, 
while  the  chorda  tympani  is  concerned,  of  course,  in  the  secre- 
tion of  saliva.  But  it  will  be  clear,  from  the  facts  of  the  case, 
that  many  nerves,  both  afferent  and  efferent,  are  concerned ; 
and  it  is  more  than  likely  that  our  explanations  of  the  (^ntire 
process  are  quite  inadequate  to  unravel  its  real  complexity. 

ThnapeutiM. — The  evidence  from  the  use  of  drugs  seems  tu 
emphasize  the  last  statement.  At  all  events,  emetics  act  in  a 
variety  of  ways,  and  differently  in  different  animals. 

The  Removal  of  Diqbsted  Products  from  the  Aliment- 
ary Canal. 

The  glands  of  the  stomach  are  simply  secretive,  and  all  ab- 
sorption from  this  organ  is  either  by  blood-vessels  directly  or 
by  lymphatics;  at  least,  such  is  the  ordinary  view  of  the  sub- 
ject—whether  it  is  not  too  narrow  a  one  remains  to  be  seen. 

It  is  important  to  reinember  that  the  intestinal  mucous 
membrane  is  supplied  not  only  with  secreting  glands  but  lym- 
phatic tissue,  in  the  form  of  the  solitary  and  agminated  glands 
(Peyer's  patches)  and  thickly  studded  with  villi,  giving  the 
I'mall  gut  that  velvety  appearance  appreciable  even  by  the 
naked  eye. 

It  wUl  not  be  forgotten  that  the  capillaries  of  the  digestive 
organs  terminate  in  the  veins  of  the  portal  system,  and  that  the 
blood  from  these  parts  is  conducted  through  the  liver  before  it 
reaches  the  general  circulation. 

The  lymphatics  of  these  organs  form  a  part  of  the  general 
lymphatic  eystem  f)f  the  body ;  but  the  peculiar  way  in  which 
absorption  is  effected  "hj  villi,  and  the  fc  ot  that  the  Ijrmphatics 
of  the  intestbie,  etc.,  at  one  time  (fasting^  contain  ordinary 
lymph  and  at  another  (after  meals)  the  products  of  digestion, 
imparts  to  them  a  physiological  character  of  their  own. 

Absorption  will  be  the  better  understood  if  we  treat  now  of 
lymph  and  chyle  and  \,he  lymph  vascular  system,  which  were 
purposely  postponed  till  the  present;  though  its  connection 
with  the  vascular  system  is  as  close  and  important  as  with 
the  digestive  organs. 

The  lymphatic  system,  as  a  whole,  more  closely  resembles 
the  venous  than  the  arterial  vessels.    We  may  speak  of  lym- 


342 


ANIMAL  PHYSIOLOGY. 


phatio  capillaries,  which  are,  in  essential  points 
of  structure,  like  the  arterial  capillaries ;  while 
the  larger  vessels  may  be  compared  to  veins, 
though  thinner,  being  provided  with  valves  and 
having  very  numerous  anastomoses.  These 
lymphatic  capillaries  begin  in  spaces  between 
the  tissue-cells,  from  which  they  take  up  the 
effete  lymph.  It  is  interesting  to  note  that 
there  are  also  perivascular  lymphatics,  the  ex- 
istence of  which  again  shows  how  close  is  the 
relation  between  the  blood  vascular  and  lym- 
phatic systems,  and  as  we  would  suppose,  and 
as  is  actually  found  to  be  the  case,  between  the 
contents  of  each. 

Lynph  ud  Chyle. — If  one  compares  the  mes- 
entery in  a  kitten,  when  fasting,  with  the  same 
part  in  an  animal  that  was  killed  some  hours 
after  a  full  meal  of  milk,  it  may  be  seen  that 
the  formerly  dear  lines  indicating  the  course  of 
ne  m-vai»«i  ot  tie  lymphatics  and  ending  in  glands  have  in 
ijnqphatic»(SMve7).  the  latter  case  become  whitish  (hence  their 
name,  Iticteala),  owing  to  the  absorption  of  the  emulsified  fat  of 
the  milk. 


rta.  M.-0riste  «( I 
nMMiwmMI — 
L :  A,  ortgte  ( 

OUMrCMMH. 


J  (attM-  LMdoto).  I.  From  eNrMJ 
c) :  s, Ijrmpb-OMiata oammtwiaiitecbr 
'  I  IV  uSm  of  Ijnnpli-OMuai;  ff,  K,  w 


Xwtth 


of  dlaoliraim  of 
lum.    u.  NriTM- 


..,_j«gtMiMifHa 


mmmm<' 


ential  points 
laries;  while 
red  to  veins, 
^h  valves  and 
OSes.  These 
aces  between 
take  up  the 
to  note  that 
latics,  the  ex- 
w  close  is  the 
lar  and  lym- 
suppose,  and 
,  between  the 

tares  the  mes- 
^th  the  same 
d  some  hours 
f  be  seen  that 
'  the  course  of 
ands  have  in 
(hence  their 
lulsified  fat  of 


Im  of  dlwliraim  of 
wMiIfmiSaiVMal 
dMllum.    u.  Nrivas- 


DIOBSTION  OF  FOOD. 


348 


Microscopic  examination  shows  the  chyle  to  contain  (when 
coagulated)  fibrin,  many  leucocytes,  a  few  developing  red  cor- 
puscles, an  abundance  of  fat  in  the  for  Ji  both  of  very  minute 
oil-globules  and  particles  smaller  still. 


Fro. )».— MttaUnmCnMidaodMninorrab-      Vw.  M.— VBH  fliled  with  tet,  firom  amdl 
Mt,  two  bom  anarluTtacbcM  fed  with  iatoMiie  oC  ««  «nanled  orimiMU,  one 

nMltodlwtt«r(nink*).  bowaflardMlhd'Uiiln). 

There  are  also  present  fatty  acids,  soaps  small  in  quantity 
as  compared  with  the  neutral  fats,  also  a  little  cholesterin  and 
lecithin.    But  chyle  varies  very  ^ 

widely  even  in  the  same  ammal 
at  different  times.  To  the  above 
must  be  added  proteids  (fibrin, 
serum-albumin,  and  globulin); 
extractives  (sugar,  urea,  lea- 
cli ) ;  and  salts  in  which  sodium 
chloride  is  abundant. 

The  composition  of  lymph  is 
so  similar  to  that  of  chyle,  and 
both  to  blood,  that  lymph 
might,  with  a  fair  degree  of  ac- 
curacy, be  regarded  as  blood 
wi^out  its  red  corpuscles,  and 
chyle  as  lymph  with  much  neu- 
tral fat  in  a  vwy  fine  state  of 
division. 

some  bimfam  uid  amphibians,  there  are  lymph  hearts. 

In  tl*  ftfog  timre  are  two  ouBtBa/ry  and  two  aaoral  lymph 
hearte.  Tlie  latter  are,  «[^pecially,  easily  seen,  and  there  is  no 
doubt,  that  they  are  ttodw  the  control  of  the  nervous  system. 


Fw.  m.-^Ck^  Men  Jram  «he. 


^fe»^ 


erimtaial 
Dke).   BbowB 
SnegniBalM 


iftfittTS.— In  some  fishes, 


M4 


ANIMAL  PHT8L0L00T. 


In  the  mAmmalB  no  such  special  helps  for  the  propulsion  of 
lymph  exist.    .. 

.     Ther^  is  little  doubt  that  the  blood -pressure  is  always 
higher  than  the  lymph-pressure^  and  when  the  blood-vessels 


t^^am^uT ^^w««Snflt«Hbiet  Jut  More  it  mptlw  86lo'tii»«iic««yifeBi 


tdhgrU 

are  dilated  the  fluid  within  the  perivwoular  lymph-channels  is 
likely  ccMnpreased ;  mviKmlar  exercise  must  act  on  the  lymph- 
channels  as  on  veins,  both  being  provided  with  valves,  though 
themselves  readily  compressible ;  the  inspiratory  efforts,  e^ 
cially  when  forcible, assist  in  two  ways:  by  the  compressing 
effect  of  the  respiratory  muscles,  and  by  the  aspirating  effect 
of  the  negative  pressure  within  the  thorax,  producing  a  similar 
aspirating  effect  within  the  great  veins,  into  which  the  large 
lymphatic  trunks  empty.  The  latter  are  provided  at  this  point 
with  valves,  so  that  there  is  no  back-flow;  and,  with  the  posi- 
tive pressure  within  the  large  lyai^tic  trunks  (thoracic  duct, 
etc.),  the  idiypieitl  conditions  are  favorable  to  the  outflow  of 
lymph  or  ok^le. 


DIGESTION  OF  FOOD. 


845 


I  is  always 
lood-vessels 


Our  knowled^  of  the  nature  of  the  passage  of  the  chyle 
from  the  intestines  into  the  blood  is  now  dearer  than  it  was  till 
recently,  though  still  incomplete. 

The  exact  structure  of  a  villus  is  to  be  carefully  considered. 
If  we  assume  that  the  muscular  cells  in  its  structure  have  a 
rhythmically  contractile  function,  the  blind  terminal  portion 
of  the  lacteal  inclosed  within  the  villus  must,  after  being 
emptied,  act  as  a  suction-piunp  to  some  extent;  at  all  events, 
the  conditions  as  to  pressure  would  be  favorable  to  inflow  of 
any  material,  especially  fluid  without  the  lacteal.  The  great 
diiBculty  hitherto  was  to  understand  how  the  fat  found  its 


to  duot;  S,  T«oep- 


i-chahnelsis 
the  lymph- 
lures,  though 
efforts,  espe- 
comiff^Ming 
rating  effect 
ing  a  similar 
ch  the  large 
at  this  point 
ith  the  pofii- 
horacic  duct, 
le  outflow  of 


Fro.  M. 


way  through  the  vilius  into  the  blood>  for,  thftt  most  of  it 
passes  in  this  direction  there  is  little  doubt. 

It  is  now  known  thttt  leucocytes  (amoeboids,  phagocytes) 
migrate  from  wiihiii  the  villus  oatwftrd,  and^nay  even  reach 
its  surface;  that  they  take  up  (eat)  f^t^pwrticles  from  the 


846 


ANIMAL  PHYSIOIAXJY. 


;^?<^' 


^1^^ 


^^>^-ss^ 


^^\ 


'/:■  -ii:  ^- 


..■  -.HIT' 

r  ~ -"           ^     '   1 

1^  ; 

E^  m 


l^fWi^iMHr:.. 


rm.  iiao.  atwnx*, 


iMjvlitly  r«dHiMd  firam  • 


r,  Ji^  Hi  a«  Jl« 


epithelium  of  the  yiUns,  ond^  independently  tiiemaelves,  carry 
them  inward, reach  the  central  lacteal  and  breakup, thus  releas- 
ing the  fat.    How  the  fat  gets  into  the  covering  epithelium  is 


MaBiiiwWfiiiwtn 


'm 


-'W' 


^y^''* 
^'*^j 


taMIB)(«ltar 

ob ;  f,  dnadaamn : 


nmlyes,  cany 
p^thnsreleas- 
epithelitun  is 


DIGESTION  OF  FOOD. 


347 


not  yet  so  fully  known — possibly  by  a  simi- 
lar inceptive  process ;  nor  is  it  ascertained 
what  constructive  or  other  chemical  pro- 
cesses they  may  perform ;  though  it  is  not 
at  all  likely  that  the  work  of  the  amoeboid 
cells  is  confined  to  the  transport  of  fat 
alone,  but  that  other  matters  are  also  thus 
removed  inward  to  the  lacteal. 

liptrimMteL— If  two  frogs  under  the 
influence  of  urari,  to  remove  the  effect  of 
muscular  movements,  be  placed  under  ob- 
servation, the  one  having  its  brain  and 
spinal  cord  destroyed,  the  other  intact,  in 
both  the  aorta  divided  across,  and  normal 
saline  solution  injr  d  into  the  posterior 
lymph-sac  (benea  xe  skin  of  the  back), 
it  will  be  found,  on  suspending  the  two 
by  the  lower  jaw,  that,  in  the  frog, with 
the  nerve  -  centers  uninjured,  abundance 
of  saline  fluid  is  taken  up  from  the  dor- 
sal sac  and  expelled  through  the  aorta, 
but  in  the  other  case  none,  the  heart  remaining  all  but  empty. 


n». 


ANIMAL  PHYSIOLOGY. 


Different  interpretations  have  been  put  upon  this  experi- 
ment.   Some  point  to  it  as  clear  proof  of  the  influence  of  the 


B 


lep 


Fio.  IM.-A.  SmUob of  rmmtinlimtA  i 
0T, ■trialed  koidtr:  c  IjrnvkMdli ^e*,^ 

4lMori<t:oB0l«MfM').  e]^< 


a  !  70ii  system  directly ;  to  others  it  seems  that  the  failure  of 
vosorption  is  owing  to  the  grreatly  dilated  conditkm  of  the 
jlood-vessels,  cojosequent  upon  the  loss  of  arterial  tone,  the 
blood  remaixdng  in  the  veihs,  and  the  ciroulation  \mAg,  in  fact, 
practically  arrested.  It  oertflonlycan  n^c^  be  claimed  that  the 
first  coni^ludon  necessarily  fdlo%s  from  the  experiment;  the 
second  may  be>a  partial  explanatibn  of  the  iailu*©  of  absorp- 
tion; but,  when  a  multitude  of  other  facte  are  ^ken  into 
account,  tihere  seems  little  reason  to  doubt  that  so  important  a 
process  ae  absorption  can  not  f ail  ip  be  mgulated  by  tiie  nerv- 
ous center?.  The  danger  of  foimding  any  impbiftalat  conclu- 
sion on  a  single  experiment  is  very  great. 

Again,  if  the  leg  of  a  hog,  exolu^ve  of  the  nerves,  be  liga- 
tured, the  limb  will  be  foia^.  to  swell  nqiidly  if  placed  in  water, 
which  is  not  true  of  a  dead  limb.  This  is  addiaoed  as  evidence 
for  the  iiidependenee  of  the  abtewptive  process  and  the  circula- 
tion; and;  since  section  of  tlie  sciatie  nerve  is  said  to  arrest 
absorption,  such  an  experiment,  taken  together  with  the  two 


his  experi- 
mce  of  the 


tH::  ' 


■^ 


ep,  eiittlielliim ; 
itnl  lactaid  ooo- 

MliMdiDllIK  tat 


le  f ailiire  of 
tion  of  the 
il  tone,  the 
dng,  in  fact, 
ed  that  the 
riment;  the 
>  of  abnorp- 
^ken  into 
important  a 
Yjf  ttie  nerv- 
babt  condu- 


-ves,  be  liga- 
»d  in  water, 
as  evidence 
the  circula- 
id  to  arrest 
ith  the  two 


lAiltMijiiiiJWitiiiA'jgigi 


^ 


r 


^. 


.^;^. 


v^, 


^.v^. 


k 

I 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


1.0 


I.I 


11.25 


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Hi 

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2.0 


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PhotDgraphic 

Sciences 

Corporation 


23  WIST  MAIN  STRUT 

WnSTIR.N.Y.  14SM 

(716)t72-4S03 


Wit".  :_.;,..^.;i*i:|',-.v_i3i-«**t.--  .<?:^e*i;6«#i¥  riii^,--*-^t.-.,^j^V"W<*Mt»-«e«^v-;-=*':-^.^,^*¥^f-. 


CIHM/ICMH 

Microfiche 

Series. 


CIHIVI/ICIVIH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Microraproductions  /  Institut  Canadian  da  microraproductions  historlquas 


'■  '-Hiifh 


H 


/^ 


t7sW''sr^f.mmimi^sB3i 


DIGESTION  OF  FOOD. 


849 


previous  ones,  points  in  the  direction  of  the  control  of  this 
process  by  the  nervous  system.  But  if  the  views  we  hold  of 
the  absolute  dependence,  especially  in  the  higher  animals,  of 
all  vital  processes  on  the  nervous  system  are  correct,  it  fol- 
lows, as  a  matter  of  course,  that  absorption  in  living  tissues, 
which  we  do  not  regard  as  wholly  explicable  by  any  physical 
process,  but  as  bound  up  with  all  the  functions  of  cell-life, 
must  be  dependent  on  that  connection  we  are  endeavoring  to 
emphasize  between  one  tissue  and  another,  and  especially  the 
dominating  tissue,  the  nervous  system. 

There  are  two  points  that  are  very  far  from  being  deter- 
mined :  the  one  the  fate  of  the  products  of  digestion ;  the  other 
the  exact  limit  to  which  digestion  is  carried.  How  much— 
e.  g.,  of  proteid  matter— does  actually  undergo  conversion  into 
peptone ;  how  miich  is  converted  into  leucin  and  tyrosin ;  or, 
again,  what  proportion  of  the  albuminous  matters  are  dealt  with 
as  such  by  the  intestine  without  conversion  iiito  peptone  at  all, 
either  as  soluble  proteid  or  in  the  form  of  solid  particles  ? 

1.  It  is  generally  believed  that  soluble  sugard  are  absorbed, 
usually  after  conversion  into  maltose  or  glucose,  by  the  capil- 
laries of  the  stomach  and  intestine. 

2.  There  is  some  positive  evidence  of  the  presence  of  fats, 
soaps,  and  sugars  in  unusual  amount  after  a  meal  in  the  portal 
vein,  which  implies  removal  from  the  intestinal  contents  by 
the  capillaries,  though,  so  far  as  experiment  goes,  the  fat  is 
chiefly  in  the  form  of  sdaps. 

Certain  experiments  have  been  made  by  ligating  the  pyloric 
end  of  the  stomach,  by  introducing  a  cannula  into  the  thoracic 
duct,  so  as  to  continually  remove  its  contents,  etc.  But  we  are 
surprised  that  serious  conclusions  should  h&ve  been  drawn  under 
such  circumstances,  seeing  that  the  natural  conditions  are  so 
altered.  What  we  wish  to  get  at  in  physiology  is  the  normal 
function  of  parts,  and  not  the  possible  results  after  onr  inter- 
ference. Under  such  circumstanioes  the  phenomena  may  have 
a  suggestive  but  certainly  can  not  have  a  conclusive  value. 

It  is  a  very  striking  fact  that  little  peptone  (none,  according 
to  some  observers)  can  be  detected  even  in  the  portal  blood. 
True  it  is,  the  circulation  is  rapid  and  constant,  and  a  small 
quantity  might  escape  detection,  yet  a  considerable  amount  be 
removed  from  the  intestine  in  the  space  of  a  few  hours  by  the 
capillaries  alone.  Peptone  is  not  found  in  the  contents  of  the 
thoracic  duct. 

Recent  investigations  have  thrown  a  new  light  on  peptone. 


nmm»t 


860 


ANIMAL  PHYSIOLOGY. 


It  is  now  known  that  there  are  several  kinds  of  peptones,  a 
disclosure  for  which  we  were  not  unprepared,  considering  our 
imperfect  knowledge  of  proteids  in  general;  but  there  have 
been  other  developments  which,  on  the  supposition  that  the 
peptone  of  the  alimentary  canal  is  freely  absorbed  as  such,  are 
startling  enough.  It  has  been  shown  that  these  peptones,  at 
least  as  prepared  by  artificial  digestion,  have  three  effects  when 
injected  in  quantity  into  the  blood  of  an  animal :  They  produce 
narcosis ;  they  retard  or  prevent  coagulation  of  the  blood ;  they 
lower  blood-pressure.  The  first  effect  may  be  dependent  in 
whole  or  in  part  on  the  third. 

^ut,  inasmuch  as  the  venom  of  poisonous  reptiles,  according 
to  recent  investigations,  is  essentially  proteid  in  nature,  it  is 
plain  that  we  must  exercise  great  caution  in  drawing  conclu- 
sions in  regard  to  the  physiological  effects  of  proteid  bodies,  so 
long  as  our  knowledge  of  their  exact  chemical  composition  is 
so  imperfect.  That  the  chemist  can  make  out  no  great  differ- 
ence between  peptones  prepared  in  the  laboratory  and  the  di- 
gestive tract,  or  even  between  these  and  snake- venom,  though 
they  have  such  different  effects  when  injected  into  the  blood, 
is  clear  proof  of  how  much  we  have  yet  to  learn  of  these 
bodies. 

But  we  introduce  these  considerations  here  rather  to  show 
that  it  is  by  no  means  likely  that  any  great  quantity  of  pep- 
tones passes  into  the  blood  as  such  at  any  one  time.  It  has 
been  recently  suggested  that  peptone  is' converted  into  globulin 
in  the  liver.  But  what  proof  is  there  of  this  P  And  already 
we  have  credited  the  liver  with  a  large  share  of  work. 

For  a  considerable  period  it  has  been  customary  to  use  the  • 
terms  endosmosis  and  diffusion  in  connection  with  the  func- 
tions of  the  alimentary  canal,  and  especially  the  intestinal  tract, 
as  if  this  thin-walled  but  complicated  organ,  or  rather  collec- 
tion of  organs,  were  little  more,  so  far  as  absorption  is  con- 
cerned, than  a  moist  membrane,  leaving  the  process  of  the  re- 
moval of  digested  food  products  to  be  explained  almost  wholly 
on.  physical  principles. 

(From  such  views  we  dissent.  We  believe  they  are  opposed 
to  what  we  know  of  living  tissue  everywhere,  and  are  not  sup- 
ported by  the  special  facts  of  digestion.  When  certain  foreign 
bodies  (as  purgatives)  are  introduced  into  the  blood  or  the  ali- 
mentary canal,  that  diffusion  takes  place,  according  to  physical 
laws,  may  indicate  the  manher  in  which  the  intestine  can  act ; 
but  even  admitting  that  under  such  circumstances  physical 


[  peptones,  a 
isidering  our 
b  there  have 
lion  that  the 
i  as  such,  are 
I  peptones,  at 
)  effects  when 
rhey  produce 
3  blood ;  they 
dependent  in 

les,  according 
nature,  it  is 
iwing  conclu- 
beid  bodies,  so 
iomposition  is 

0  great  differ- 
ry  and  the  di- 
enom,  though 
ito  the  blood, 
earn  of  these 

*ather  to  show 
antity  of  pep- 
time.    It  has 

1  into  globulin 

And  already 
work. 

lary  to  rise  the  • 
nth  the  func- 
Qtestinal  tract, 
r  rather  coUec- 
>rption  is  con- 
xsdss  of  the  re- 
almost  wholly 

ley  are  opposed 
ad  are  not  sup- 
certain  foreign 
flood  or  the  ail- 
ing to  physical 
testine  can  act ; 
anoes  physical 


DIGESTION  OF  FOOD. 


861 


principles  actually  do  explain  the  whole,  which  we  do  not  grant, 
it  would  by  no  means  follow  that  such  was  the  natural  behav- 
ior of  this  organ  in  the  discharge  of  its  ordinary  functions. 

When  we  consider  that  the  blood  tends  to  maintain  an  equi- 
librium, it  must  be  evident  that  the  removal  of  substances  from 
the  alimentary  canal,  unless  there  is  to  be  excessive  activity  of 
the  excretory  organs  and  waste  of  energy  both  by  them  and 
the  digestive  tract,  must  in  some  degree  depend  on  the  demand 
for  the  products  of  digestion  by  the  tissues.  That  there  is  to 
some  extent  a  corrective  action  of  the  excretory  organs  always 
going  on  is  no  doubt  true,  and  that  it  may  in  cases.of  emergency 
be  great  is  also  true ;  but  that  this  is  minimized  in  ways  too 
complex  for  us  to  follow  in  every  detail  is  equally  true.  Diges- 
tion waits  on  appetite,  and  the  latter  is  an  expression  of  the 
needs  of  the  tissues.  We  believe  it  is  literally  true  that  in  a 
healthy  organism  the  rate  and  character  of  digestion  and  of 
the  removal  of  prepared  products  are  largely  dependent  on  the 
con^ion  of  the  tissues  of  the  body. 

(why  is  digestion  more  perfect  in  overfed  individuals  After 
a  sOort  fast  ?  The  whole  mtftter  is  very  complex,  but  we  think 
it  is  infinitely  better  to  admit  ignorance  than  attempt  to  ex- 
plain by  principles  that  doviolence  to  our  fundamental  con- 
ceptions of  life  processea  To  introduce  "  ferments  "  to  explain 
so  many  obscure  ppints  in  physiology,  as  the  conversion  of 
peptone  in  the  blood,  for  example,  is  taking  refuge  in  a  way 
that  does  no  credit  to  science. 

Without  denying  that  endosmosis,  etc.,  may  play  a  part  in 
the  vital  processes  we  are  considering,  we  believe  a  truer  view 
of  the  whole  matter  will  be  ultimately  reached.  In  the  mean 
time  we  think  it  best  to  express  our  belief  tl^t  we  are  igiiOTant 
of  the realjig^ture of  absorption  iujgreat  p^tThut weffiink 
tEK73T^"^iSiraSary  "tfifcr  w^  as  doing  for  the 

digested  food  (chyle,  etc.)  some  such  work  as  certain  other 
glands  do  for  the  blood,  we  would  be  on  the  way  to  a  truer  con- 
ception of  the  real  nature  of  the  processes.   ' 

It  would  then  be  possible  to  understand  that  proteids  either 
in  the  form  of  soluble  or  insoluble  substances,  including  pep- 
tone, might  be  taken  in  hand  and  converted  by  a  true  vital 
process  into  the  constituents  of  the  blood. 

r  If  we  were  to  regard  the  kidney  as  manufacturing  useful 
iusCead  of  harmful  products,  the  resemblance  in  behavior  would 
in  many  points  be  parallel.  We  have  seen  that  mechanical 
explanations  of  the  functions  of  the  kidney  have  failed,  and 


n'aill!i»aB5M>IW.tiW.'<H[UgWIWWi>'W(''aWllW^^  '  lUlWIW'JWIJIII>'l»iJ»..UJfeJ»Jll!lil,!IWM»Mii.lUIII)lMu.i<'IWU,i|l!l 


mmn'mmmmmmli^ 


S5i 


ANIMAL  PllYSIOLOOY. 


Chat  it  must  be  regarded  even  in  those  parts  that  eliminate 
most  water  as  a  genuine  secreting  mechanism. 

We  wish  to  present  a  somewhat  truer  conception  of  the 
lymph  that  is  separated  from  the  capillaries  and  bathes  the 
tissues. 

We  would  regard  its  separation  as  a  true  secretion,  and  not 
a  mere  diffusion  depend«9nt  wholly  on  blood-pressure.  The 
mere  ligature  of  a  vein  does  not  sufBce  to  cause  an  excess  of 
diffusion,  but  the  vaso^motor  nerves  have  been  shown  to  be 
concerned.  The  effusions  that  result  from  pathological  pro- 
cesses do  not  correspond  with  the  Ijntnph — ^that  is,  the  nutrient 
material — ^provided  by  the  capillaries  for  the  tissues.  These 
vessels  are  more  than  mere  carriers ;  they  are  secretors — ^in  a 
sense  they  are  glands.  We  have  seen  that  in  the  fcetus  they 
function  both  as  respiratory  and  nutrient  organs  in  the  allan- 
tois  and  yelk-sac,  and,  in  our  opinion,  they  never  wholly  lose 
this  function. 

The  kind  of  lymph  that  bathes  a  tissue,  we  believe,  depends 
on  its  nature  and  its  condition  at  the  time,  so  that,  as  we  view 
tissue-lymph,  it  is  not  a  mere  effusion  with  which  the  tissues, 
for  which  it  is  provided,  have  nothing  to  do.  The  differences 
may  be  beyond  our  chemistry  to  determine,  but  to  assume  that 
all  lymph  poured  out  is  alike  is  too  crude  a  conception  to  meet 
the  facts  of  the  case.  Qlands,  too,  it  will  be  remembered,  derive 
their  materials,  like  all  other  tissues,  not  directly  from  the 
blood,  but  from  the  lymph.  We  believe  that  the  cells  of  the") 
Capillaries,  like  all  others,  are  influenced  by  the  nervous  system,  [ 
notwithstanding  that  nerves  have  not  been  traced  terminating] 
in  them. 

It  is  to  be  borne  in  mind  that  the  lymph,  like  the  blood, 
receives  tissue  waste-products — in  fact,  it  is  very  important  to 
realize  that  the  lymph  is,  in  the  first  instance,  a  sort  of  better 
blood — an  improved,  selected  material,  so  far  as  any  tissue  is 
concerned,  which  becomes  gradually  deteriorated  (toe  Fig.  8S9). 

We  have  not  the  space  to  give  all  the  reasons  on  which  the 
opinions  expressed  above  are  founded ;  but,  if  the  student  has 
become  imbued  with  the  principles  that  pervade  this  work  thus 
far,  he  will  be  prepared  for  the  attitude  we  have  taken,  and 
sympathize  with  our  departures  from  the  mechanical  (physical) 
phmblogy. 

We  think  it  would  be  a  gt«at  gain  for  physiology  if  the  use 
of  the  term  "  absorption,"  as  applied  to  the  alimentary  tract, 
were  given  up  altogether,  as  it  is  sure  to  lead  to  the  substitu- 


niOBSTIOX  OF  FOOD. 


368 


at  eliminate 

ption  of  the 
i  bathes  the 

tion,  and  not 
)BSUTe.  The 
an  excess  of 
shown  to  be 
ological  pro- 
the  nutrient 
isnes.  These 
cretora — in  a 
e  fcBtus  they 
in  the  allan- 
r  wholly  lose 

ieve,  depends 
it,  as  we  view 
ti  the  tissues, 
he  differences 
0  assume  that 
ption  to  meet 
nbered,  derive 
stly  from  the 
le  cells  of  the"^ 
»rvous  system,  [ 
d  terminatingj 

ke  the  blood, 

important  to 

sort  of  better 

any  tissue  is 

(toe  Fig.  829). 

on  which  the 

le  student  has 

;his  work  thus 

tve  taken,  and 

leal  (physical) 

ogy  if  the  use 
mentary  tract, 
o  the  substitu- 


tion of  the  gross  conceptions  of  physical  processes  instead  of 
the  subtle  though  at  present  rather  indefinite  ideas  of  vital 
processes.  We  prefer  ignorance  to  narrow,  artificial,  and  erro- 
neous views. 

PAthologioaL — Under  certain  circumstances,  of  which  one-  is 
obstiruction  to  the  venous  circulation  qr  the  lymphatics,  fluid 
may  be  poured  out  or  effused  into  the  neighboring  tissues  or  the 
serous  cavities.  This  is  of  very  variable  composition,  but  always 
contains  enough  salts  and  proteids  to  remind  one  of  the  blood. 

Such  fluids  are  often  spoken  of  as  "lymph/'  though  the 
resemblance  to  normal  tissue-lymph  is  but  of  the  crudest  kind; 
and  the  condition  of  the  vessels  when  it  is  secreted,  if  such  a 
term  is  here  appropriate,  is  not  to  be  compared  to  the  natural 
separation  of  the  normal  lymph — in  fact,  were  this  not  so,  it 
would  be  like  the  latter,  which  it  is  not.  When  such  effusions 
take  place  th^y  are  in  themselves  evidence  of  altered  (and  not 
merely  increased)  function. 

Thit  iMMb — The  feeces  may  be  regarded  in  at  least  a  three- 
fold aspect.  They  contain  undigested  and  indi^tible  rem- 
nants, the  ferments  and  certain  decomposition  products  of  the 
digestive  fluids,  and  true  excretory  matters. 

In  carnivorous  and  omnivorous  animals,  including  man, 
the  undigested  materials  are  those  that  have  escaped  the  action 
of  the  secretions— such  as  starch  and  fats— together  with  those 
substances  that  the  digestive  juices  are  powerless  to  attack, 
as  homy  matter,  hairs,  elastic  tissue,  etc. 

In  vegetable  feeders  a  larger  proportion  of  chlorophyl,  cel- 
Moee,  and  starch  will,  of  course,  be' found. 

These,  naturally,  are  variable  with  the  individual,  the  spe- 
cies, and  the  vigor  of  the  digestive  oi^ns  at  the  time. 

Besides  the  above,  certain  products  are  to  be  detected  in  the 
fsBces  plainly  traceable  to  the  digestive  fluids,  and  showing 
that  they  have  undergone  chemical  decomposition  in  the  ali- 
mentary tract,  such  as  cholalic  acid,  altered,  coloring-matters 
like  urobilin,  derivable  probably  from  bilirubin ;  also  oholes- 
terine,  fatty  acids,  insoluble  soaps  (caldum,  magnesium),  to- 
gether wtth  ferments,  having  the  pn^perties  of  pepsin  and 
amylopsin.    Mucus  is  also  abundant  in  tiie  feeces. 

nV'e  know  little  of  the  excretory  products  proper,  as  they 
prolSably  normally  exist  in  small  quantity,  and  it  is  not  impos- 
sible that  some  of  the  products  of  the  decomposition  of  the 
digestive  juices  may  be  reabsorbed  and  worked  over  or  excreted 
by  the  kidneys,  etc. 


»:>:<<iCT»<,?sjitte»a.  !l*^llllA'|;lMiWMl»«W'^»>^\)^»^•^^~jall^JaMlWgta>^rt^?l>Wll4llU,^l».^Jll■^uftll^ll^lJl■>■;^ 


SM 


AinMAL  PHYSIOLOGY. 


\- 


There  is,  however,  a  recognized  non-nitrogenous  crystalline 
body  known  as  excretin,  which  contains  sulphur,  salts,  and 
pigments,  and  that  may  rank  perhaps  as  a  true  excretion  of 
th6  intestine. 

It  is  well  known  that  bacteria  abound  in  the  alimentary 
tract,  though  their  number  is  depisndent  on  a  variety  of  circum- 
stances, including  the  kind  of  food  and  the  condition  in  which 
it  is  eaten.  These  minute  organisms  feed,  of  course,  and  to  get 
their  food  produce  chemical  decompositions.  SkaUjH  and  indoi 
are  possibly  thus  produced,  and  give  the  f  eecal  odor  to  the  con- 
tents of  the  intestine.  But  as  yet  our  ignorance  of  these  mat^ 
ters  is  greater  than  our  knowledge— a  remark  which  applies  to 
the  excretory  functions  of  the  alimentary  tract  generally. 

PatludogiML — The  facts  revealed  by  clinical  and  pathological 
study  leave  no  doubt  in  the  mind  that  the  intestine  at  all  events 
may,  when  other  glands,^like  the  kidney,  are  at  fault,  undertake 
an  unusual  share  of  excretory  work,  probably  even  to  the  length 
of  discharging  urea. 

Obscure  as  the  subject  is,  and  long  as  it  may  be  before  we 
know  exactly  what  and  how  matter  is  thus  excreted,  we  think 
that  it  will  greatly  advance  us  toward  a  true  conception  of  the 
vital  processes  of  the  mammalian  body  if  we  regard  the  ali- 
mentary tract  as  a  collection  of  organs  with  both  a  secreting 
and  excreting  function ;  that  what  we  have  been  terming  ab- 
sorption is  in  the  main,  at  least,  essentially  secretion  or  an  allied 
process;  and  that  the  parts  of  this  long  train  of  organs  are 
mutually  dependent  and  work  in  concert,  so  that,  when  one  is 
lacking  in  vigor  or  resting  to  a  greater  or  less  degree,  the  others 
make  up  for  its  diminished  activity ;  and  that  the  whole  must 
work  in  harmony  with  the  various  excretory  organs,  as  an 
excretor  itself ,  and  in  unison  with  the  general  state  of  the  econ- 
omy. We  are  convinced  that  even  as  an  excretory  mechanism 
one  part  may  act  (vicariously)  for  another. 

(Pf  course,  in  disease  the  condition  of  the  fnces  is  an  indica- 
tion of  the  state  of  the  digestive  organs ;  thus  color,  consistence, 
the  presence  of  food  in  lumps,  the  odor,  and  many  other  points 
tell  a  plain  story  of  work  left  undone,  ill-done,  or  disordered 
by  influences  operating  from  within  or  fnnn  without  the  tract. 
The  intelligent  physician  acts  the  part  of  a  qualified  inspector, 
surveying  the  output  of  a  great  factory,  and  drawing  conclu- 
sions in  regard  to  the  kind  of  work  which  the  operatives  have 
performed. 


f 


DIGESTION  OF  FOOD. 


855 


[g  crystalline 
r,  salts,  and 
excretion  of 


9  alimentary 
ty  of  circum- 
ion  in  whicli 
se,  and  to  get 
liol  and  indai 
>r  to  the  con- 
»f  these  mat^ 
Lch  applies  to) 
nerally. 
[  pathological 
B  at  all  events 
lit,  undertake    . 
I  to  the  length 

be  before  we 
jted,  we  think 
:;eption  of  the 
)gard  the  ali- 
bh  a  secreting 
a  terming  ab- 
on  or  an  allied 
of  organs  are 
fc,  when  one  is 
;ree,  the  others 
lie  whole  must 
organs,  as  an 
,te  of  the  econ- 
iry  mechanism 

38  is  an  indica- 
or^  consistence, 
ly  other  points 
,  or  disordered 
ihout  the  tracti 
ified  inspector, 
rawing  conclu* 
>peratives  have 


The  Changes  produced  in  the  Food  in  the  Alimentary 

Canal. 

"We  have  now  considered  the  method  of  secretion,  the  secre- 
tions themselves,  and  the  movements  of  the  various  parts  of 
the  digestive  tract,  so  that  a  brief  statement  of  the  results  of 
all  this  mechanism,  as  represented  by  changes  in  the  food,  will 
be  appropriate.  We  shall  assume  for  the  pi^sent  that  the  effects 
of  the  digestive  juices  are  substantially  the  same  in  the  body 
as  in  artificial  digestion. 

Among  mammals  food  is,  in  the  mouth,  comminuted  (except 
in  the  case  of  the  camivora,  that  bolt  it  almost  whole,  and  the 
ruminants,  that  simply  swallow  it  to  be  regurgitated  for  fresh 
and  complete  mastication),  insalivated,  and,  in  most  species, 
chemically  changed,  but  only  in  so  far  as  starch  is  concerned. 

Deglutition  is  the  result  of  the  co-ordinated  action  of  many 
muscular  mechanisms,  and  is  reflex  in  nature.  The  oesophagus 
secretes  mucus,  which  lubricates  its  walls,  and  aids  mechan- 
ically in  the  transport  of  the  food  from  the  mouth  to  the  stom- 
ach. In  the  stomach,  by  .the  action  of  the  gastric  juice,  food 
is  further  broken  up,  the  proteid  covering  of  fat-cells  is  digested, 
and  the  structure  of  muscle,  etc.,  disappears.    Proteid  matters 


rm.  MH.—1imtn  tokcotnu 

tood  (•ftir  BNnanl).   a,  <  


[•ftar  BNoanl).  a, 
darflban  tatn^biah 
i;  g,m<iteculTtti 


856 


ANIMAL  PUYSlQIiOOY. 


;. 


I- 


become  peptone,  and  in  some  animals  fat  is  split  up  into  free 
fatty  acid  and  glycerine ;  but  the  digestion  of  fat  in  the  stom- 
ach is  very  limited  at  best,  and  probably  does  not  go  on  to 
emulsification  or  saponification.  The  digestion  of  starch  con- 
tinues in  the  stomach  until  the  reaction  of  the  food-mass  be- 
comes acid.  This,  in  the  hog  may  not  be  far  from  one  to  two 
hours,  and  the  amylolytio  ferment  acts  with  great  rapidity  even 
without  the  body.  The  food  is  moved'  about  to  a  certain  ex- 
tent, so  as  to  expose  every  part  freely  to  the  mucous  mem- 
brane and  its  secretions.  It  is  likely  t^t  the  sugar  resulting 
from  the  digestion  of  starch,  the  peptones,  and,  to  some  ex- 
tent, the  fat  formed  (if  any),  is  received  int)  the  blood  from 
the  stomach. 

As  the  partially  digested  mass  (chyme)  is  passed  on  into  the 
intestine  as  a  result  of  the  action  of  the  alkaline  bile,  the  para- 
peptone,  pepsin,  and  bile-salts  are  deposited.  Certain  of  the 
constituents  of  digestion  are  thus  delayed,  a  portion  of  the  pep- 
sin is  probably  absorbed,  either  altered  or  unaltered,  and  pep- 
sin is  thus  got  rid  of,  making  the  way  clear,  so  to  speak,  for 
the  action  of  trypsin.  At  all  events,  digestion  in  one  part  of 
the  tract  is  antagonized  by  digestion  in  another,  but  we  must 
also  add  supplemented. 

The  fat,  which  had  been  but  little  altered,  is  emulsified  by 
the  joint  action  of  the  bile  and  pancreatic  secretion ;  a  portion 
is  saponified,  which  again  helps  in  emulsification,  while  an 
additional  i>art,  in  form  but  little  changed,  is  probably  dealt 
with  by  the  absorbents. 

Proteid  digestion  is  continued,  and,  besides  peptones,  ni- 
trogenous crystalline  bodies  are  fofmed  (lencin  and  tyrosin), 
but  under  what  conditions  or  to  what  extent  is  not  known ; 
though  the  quantity  is  likely  very  variable,  both  with  the  spe- 
cies of  animitl  and  the  circumstances,  such  as  quantity  and 
quality  of  food ;  and  it  is  likely  also  dependent  not  a  little  on 
the  rate  of  absorption.  It  seems  altogether  probable  that  in 
those  that  use  an  excess  of  nitrogenous  food  mor?  of  these 
bodies  are  formed,  and  thus  give  an  additional  work  to  the  ex- 
creting organs,  including  the  Uver.  But  the  absence  of  albu- 
min from  healthy  faeces  points  to  the  complete  digestion  of 
proteids  in  the  alimentary  canaL  Plainly  the  chief  work  of 
intestinal  digestion  is  begun  and  carried  on  in  the  upper  part 
of  the  tract,  where  the  ducts  of  the  main  glands  are  to  be 
found. 

The  contents  of  the  intestine  tmKna.  with  bacteria,  though 


I 
" 


DiaBSTION  UP  FOOD. 


867 


ip  into  free 
in  the  atom- 
Dt  go  on  to 
starch  con- 
od-mass  be- 
.  one  to  two 
ftpidity  even 
I  certain  ex- 
acous  mem-    ^ 
;ar  resulting 
to  some  ex- 
9  blood  from 

1  on  into  the 
ile,  the  para- 
>rtain  of  the 
n  of  the  pep- 
red,  and  pep- 
to  speak, for 
1  one  part  of 
but  we  must 

nnulsified  by 
on ;  a  portion 
on,  while  an 
robably  dealt 

peptones,  ni- 
and  tyrosin), 
)  not  known; 
with  the  spe- 
quantity  and 
not  a  little  on 
»bable  that  in 
Enor9  of  these 
rork  to  the  ex- 
tsence  of  albu- 
B  digestion  of 
chief  work  of 
the  upper  part 
ids  are  to  be 

toteria,  though 


these  are  probably  kept  under  control  to  some  extent  by  the 
bile,  the  functions  of  which  as  an  antiseptic  we  have  already 
considered. 

The  removal  of  fats  by  the  villi  will  be  shortly  considered. 
The  other  products  of  digestion  probably  find  their  way  into 
the  general  circulation  by  the  portal  blood,  passing  through 
the  liver,  which  organ  modifies  some  of  them  in  ways  to  be 
examined  later. 

The  valmdM  conniventes  greatly  increase  the  surface  of  the 
intestine,  and  retard  the  movements  of  the  partially  digested 
mass,  both  of  which  are  favorable.  The  peristaltic  movements 
of  the  small  gut  serve  the  obvious  purpose  of  moving  on  the 
digesting  mass,  thus  making  way  for  fresh  additions  of  chyme 
from  the  stomach,  and  carrying  on  the  more  elaborated  con- 
tents to  points  where  they  can  receive  fresh  attention,  both 
digestive  and  absorptive. 

Goapanti?*. — ^In  man,  the  camivora,  and  some  other  groups, 
it  is  likely  that  digestion  in  the  large  intestine  is  slight,  the 
work  being  mostly  completed— at  all  events,  so  far  as  the  action 
of  the  secretions  is  conoenied— before  this  division  of  the  tract 
is  reached,  though  doubtless  absorption  goes  on  there  also. 
The  muscular  strength  of  this  gut  is  important  in  the  act  of 
defecation. 

But  the  great  size  of  the  large  intestine  in  ruminants— in 
the  horse,  etc.— together  with  the  bulky  character  of  the  food 
of  such  animals,  points  to  the  existence  of  possibly  extensive 
processes  of  which  we  are  ignorant.  It  is  generally  believed 
that  food  remains  but  a  short  time  in  the  stomach  of  the  horse, 
and  that  the  ceecum  is  a  sort  of  reservoir  in  which  digestive 
processes  are  in  progress,  and  also  for  water. 

FermerUaiions  go  on  in  the  intestine,  and  probably  among 
ruminants  they  are  numerous  and  essential,  though  our  actual 
knowledge  of  the  subject  is  very  limited. 

The  gases  found  in  the  human  stomach  are  atmospheric  air 
(s¥n»llowed)  and  carbon  dioxide,  derived  from  the  blood.  Those 
of  the  intestine  are  nitrogen,  hydrogen,  carbonic  anhydride, 
Bulphureted  hydrogen,  and  marsh-gas,  the  quantity  varying 
considerably  with  the  diet 

fttiukfiflaL — In  subjects  of  a  highly  neurotic  temperament 
and  imstable  nervous  system  it  sometimes  happens  that  im- 
mense quantities  of  gas  are  belched  from  an  empty  stomach  or 
distend  the  intestines. 

It  is  known  that  the  oxygen  swallowed  is  absorbed  into  the 


-x-^<T!%v.'!^^^-9-nv^, 


■;^;^?^AmimllKmiV.lm»immumlf\lwmM<lii^Mlmmm 


I 

I    ■ 


858 


ANIMAL  FHTSIOLOOT. 


blood,  and  the  carbonic  anhydride  found  in  the  stomach  de- 
rived from  that  fluid. 

It  will  thus  be  seen  that  the  alimentary  tract  has  not  lost 
its  respiratory  functions  even  in  man,  and  that  these  may  in 
certain  instances  be  inordinately  developed  {reveraion). 


\ 


-\ 


^ 


Spbcial  Oonsidkrations. 

It  is  a  matter  well  recognized  by  those  of  much  experience 
in  breeding  and  keeping  animals  with  restricted  freedom  and 
under  other  conditions  differing  widely  from  the  natural  ones 
— ^l  e..  those  under  which  the  animals  exist  in  a  wild  state — ^that 
the  nature  of  the  food  most  vary  from  that  which  the  imtamed 
ancestors  of  our  domestic  animals  used.  Food  may  often  with 
advantage  be  cooked  for  the  tame  and  confined  animal.  The 
digestive  and  the  assimilative  powers  have  varied  with  other 
changes  in  the  organism  brought  about  by  the  new  surround- 
ings. So  much  is  this  the  case,  that  it  is  necessary  to  resort  to 
common  experience  and  to  more  exact  experiments  to  ascertain 
the  best  methods  of  feeding  animals  for  fattening,  for  work, 
or  for  breeding.  Inferences  drawn  from  the  feeding  habits  of 
wild  animals  allied  to  the  tame  to  be  valuable  must  always, 
before  being  applied  to  the  latter,  be  subjected  to  correction 
by  the  results  of  experience. 

To  a  still  greater  degree  does  this  apply  to  man  himself. 
The  greater  his  advances  in  civilization,  the  more  he  departs 
from  primitive  habits  in  other  respects,  the  more  must  he  de- 
part in  his  feeding.  With  the  progressive  development  of 
man's  cerebrum,  the  keener  struggle  for  place  and  power,  the 
more  his  nervous  energies  are  diverted  from  the  lower  func- 
tions of  digestion  and  assimilation  of  food ;  hence  the  greater 
need  that  food  shall  be  more  carefully  selected,  and  more 
thoroughly  and  scientifically  prepared.  Not  only  so,  but,  with 
our  increasing  refinement,  the  progress  of  digestion  to  suc- 
cessful issues  demands  that  the  senses  of  man  be  jninistered 
to  in  order  that  there  be  no  interferences  in  the  central  nerv- 
ous system,  on  the  one  hand,  and  every  encouragement  to  the 
latter  to  furnish  the  necessary  nervous  impulses  to  the  digest- 
ive organs  and  the  tissues  in  every  part  of  the  organiran:  for 
it  is  not  enough  that  food  be  digested  in  the  ordinary  sense : 
it  must  also  be  built  up  into  the  tissues,  a  process  depending, 
as  we  shall  endeavor  to  show  later,  on  the  nervous  system. 

The  ''gastronomic  art"  has,  therefore,  become  of  great  im- 


DIGESTION  OF  FOOD. 


8ff» 


itomacli  de- 
has  not  lost 
hese  may  in 
ion). 


h  experience 
freedom  and 
natural  ones 
d  state— that 
the  untamed 
ly  often  with 
gmimal.    The 
d  with  other 
ew  snrround- 
y  to  resort  to 
8  to  ascertain 
Qg,  for  work, 
iing  habits  of 
must  always, 
to  correction 

man  himself, 
re  he  departs 
s  must  he  de- 
ivelopment  of 
nd  power,  the 
le  lower  func- 
ce  the  greater 
ed,  and  more 
y  so,  but,  with 
;estion  to  sue* 
be  juinistered 
i  central  nerv- 
igement  to  the 
I  to  the  digest- 
organiran:  for 
>rdinary  sense: 
;es8  depending, 
us  system, 
le  of  great  im- 


portance. It  is  as  yet  more  of  an  art  than  a  science ;  the  cook 
has  outstripped  the  physiologist,  if  not  the  chemist  also,  in  this 
direction. 

We  can  not  explain  fully  why  food  prepared  by  certain 
meiliods  and  served  in  courses  of  a  certain  established  order  is 
so  suited  to  refined  man.  A  part  is  known,  but  a  great  deal 
remains  to  be  discovered.  We  may,  however,  notice  a  few 
points  of  importance  in  regard  to  the  preparation  of  food. 

It  is  now  well  established  by  experience  that  animals  kept 
in  confinement  must  have,  in  order  to  escape  disease  and  attain 
the  best  results  on  the  whole,  a  diet  which  not  only  imitates 
that  of  the  corresponding  wild  forms  generally,  but  even  in 
details,  with,  it  may  be,  altered  proportions  or  added  constitu- 
ents, in  consequence  of  the  difference  in  the  environment.  To 
illustrate :  poultry  can  not  be  kept  healthy  confined  in  a  shed 
without  sand,  gravel,  old  mortar,  or  some  similar  preparation ; 
and  for  the  best  results  they  must  have  green  food  also,  as 
lettuce,  cabbage,  chopped  green  clover,  grass,  etc.  They  must 
not  be  provided  with  as  much  food  as  if  they  had  the  exercise 
afforded  by  running  hither  and  thither  over  a  large  field.  We 
have  chosen  this  case  bebause  it  is  not  commonly  recognized 
that  our  domesticated  birds  have  been  so  modified  that  special 
study  must  be  made  of  the  environment  in  all  cases  if  they 
are  not  to  degenerate.  The  facts  in  regard  to  homed  cattle, 
horses,  and  dogs  are  perhaps  better  known. 

But  all  these  instances  are  simple  as  compared  with  man. 
The  lower  mammals  can  live  and  flourish  witii  comparatively 
little  change  of  diet ;  not  so  man.  He  demands  diet  not  only 
dissimilar  in  its  actual  grosser  nattire,  but.differently  prepared. 
In  a  word,  for  the  efferent  oarvous  impulses,  on  which  the 
digestive  processes  depend  to  be  properly  supplied,  it  has  be- 
come necessary  that  a  variety  of  afferent  impulses  (through 
eye,  ear,  nose,  palate)  reach  the  nervous  centers,  attuning  them 
to  harmony,  so  that  they  shall  act,  yet  not,  interfere  With  one 
another. 

^Oooking  greatly  alters  the  chemical  composition,  the  me- 
chanical condition,  and,  in  consequence,  the  flavor,  the  digesti- 
bility, and  the  nutritive  value  of  foods.  To  illustrate:  meat  in 
its  raw  condition  would  present  mechanical  difficulties,  the  di- 
gestive fluids  permeating  it  less  completely ;  an  obstacle,  how- 
ever, of  far  greater  magnitude  in  the  case  of  most  vegetable 
foods.  By  cooking,  certain  chemical  compounds  are  replaced 
by  others,  while  some  may  be  wholly  removed.    As  a  rule. 


.U.VJjJ.■^"^ffttl^l,J^^^j^■,;aaWi^!Jt^J-:M'-S^iJ!H^!■^^'^Wg|T-^..  ita^l.-jl8L»»^ 


800 


ANIMAL  I  HY8I0L00Y. 


i^ 


s. 


ym^ 


boiling  is  not  a  good  form  of  preparing  meat,  because  it  with- 
draws not  only  salts  of  importance,  but  proteids  and  the  ex- 
tractives— nitrogenous  and  other.  Beef-tea  is  valuable  chiefly 
because  ot  these  extractives,  though  it  also  contains  a  little 
gelatine,  albumin,  and  fats.  Salt  meat  furnishes  less  nutri- 
ment, a  large  part  having  been  removed  by  the  brine;  not- 
withstanding, all  persons  at  times,  and  some  frequently,  find 
such  food  highly  beneficial,  the  effect  being  doubtless  oot  con- 
fined to  the  alimentary  tract. 

Meat,  according  to  the  heat  employed,  may  be  eo  cooked  as 
to  retain  the  greater  part  of  its  juices  within  it  or  the  reverse. 
With  a  high  temperature  (66°  to  70"  C.)  the  outside  in  roasting 
may  be  so  quickly  hardened  as  to  retain  the  juices. 

In  feeding  dogs  it  is  both  physiological  and  economical  to 
give  the  animal  the  broth  as  well  as  the  meat ',  'i;clf .    The  poor 
man  may  get  excellent  food  cheaply  by  using  *<ot  alone  the 
meat  of  the  shank  of  beef,  but  the  extractives  derived  from  it. 
There  is  much  waste  not  only  by  the  consumption  of  more  food^ 
than  is  necessary,  but  by  the  purchase  of  kinds  in  which  thaty 
:  important  class  of  bodies,  the  proteids,  comes  at  too  high  aj 
price. 

fit  is  remarkable  in  the  highest  degree  that  man's  appetite, 
or  the  instinctive  choice  of  food,  has  proved  wiser  tluui  our 
science.  It  would  be  impossible  even  yet  to  match,  by  calcula- 
tions based  on  any  data  we  can  obtain,  a  diet  for  each  man  equal 
upon  the  whole  to  what  his  instincts  prompt.  With  the  lower 
mammals  we  can  prescribe  with  greater  sucoesa  At  the  same 
time  chemical  and  physiological  science  can  lay  down  general 
principles  based  on  actual  experience,  which  may  serve  to  cor- 
rect some  artificialities  acquired  by  perseverance  in  habits  that 
were  not  based  on  the  true  instincts  of  a  sotmd  body  and  a 
healthy  mental  and  moral  nature;  for  the  influence  of  the 
latter  can  not  be  safely  ignored  even  in  such  discussions  as  the 
present.  These  remarks,  however,  are  meant  to  be  suggestive , 
rather  than  exhaustive. 

We  may  with  advantage  inquire  into  the  nature  of  hunger 
and  thirst  These,  as  we  know,  are  safe  guides  usually  in  eat- 
ing and  drinking. 

^£pter  a  long  walk  on  a  warm  day  one  feels  thirsty,  the 
mouth  is  usually  dry:  at  all  events,  moistening  the  mouth, 
especially  the  back  of  it  (pharjrnx),  will  of  itself  partially  re- 
lieve thirst.  But  if  we  remain  quiet  for  a  little  time  the  thirst 
grows  less,  even  if  no  fluid  be  taken.    The  dryness  has  been 


kuse  it  witii- 
and  the  ex- 
lable  chiefly 
ains  a  little 
)  less  nutri- 
brine;  not- 
luently,  find 
iless  DGt  con- 
so  cooked  as  *' 
■  the  reverse, 
e  in  roasting 

• 

conomical  to 
If.  The  poor 
>ot  alone  the 
rived  from  it. 
of  more  food> 
n  which  tiiat/ 
bt  too  high  tk) 

Au's  appetite, 
user  than  onr 
h,  by  calcula- 
ich  man  equal 
^ith  the  lower 
At  the  same 
down  general 
r  serve  to  cor- 
in  habits  that 
d  body  and  a 
Inence  of  the 
lussiono  as  the 
be  suggestive 

ore  of  hunger 
usually  in  eat- 

Is  thirsty,  the 
Lg  tiie  mouth, 
If  partially  re- 
fcime  the  thirst 
ness  has  been 


DIOBSTION  OF  FOOD. 


861 


relieved  by  the  natural  secretions.  If,  however,  fluid  be  intro- 
duced into  the  blood  either  directly  or  through  the  alimentary 
canal,  the  thirst  is  also  relieved  speedily.  7he  fact  that  we 
know  when  to  stop  drinking  water  shows  of  itself  that  there 
must  be  local  sensations  that  guide  us,  for  it  is  not  possible  to 
believe  that  the  whole  of  the  fluid  taken  can  at  once  have  en- 
tered the  blood. 

Again,  in  the  case  of  hunger,  the  introduction  of  innutritions 
matters,  as  earth  or  sawdust,  will  somewhat  relieve  the  urgent 
sensations  in  extreme  cases ;  as  will  also  the  use  of  tobacco  by 
smokers,  or  much  mental  occupation,  though  the  latter  is 
rather  illustrative  of  the  lessening  of  l^e  consciousness  of  the 
ingoing  impulses  by  diverting  the  attention  from  them.  But 
hunger,  like  thirst,  may  be  mitigated  by  injections  into  the 
intestines  or  the  blood.  It  is,  therefore,  clear  tiiat,  while  in  the 
case  of  hunger  and  thirst  there  is  a  local  expression  of  a  need, 
a  peculiar  sensation,  more  pronounced  in  certain  parts  (the 
fauces  in  ihe  case  of  thirst,  the  stomach  in  that  of  hunger), 
yet  these  may  be  appeased  from  within  through  the  medium 
of  the  blood,  as  well  as  from  without  by  the  contact  of  food  or 
water,  as  the  case  may  be.' 

Up  to  the  present  we  have  assumed  that  the  changes 
wrought  in  the 'food  in  the  alimentary  tract  were  identical 
with  those  produced  by  the  digestive  ferments  as  obtained  by 
extracts  of  the  organs  naturally  producing  them.  But  for 
many  reasons  it  seems  probable  that  artificial  digestion  can  not 
be  regarded  as  parallel  with  the  natural  processes  except  in  a 
very  general  way.  When  we  take  into  account  the  absence  of 
muscular  movements,  regulated  according  to  no  rigid  prin- 
ciples, but  varying  with  innumerable  circumstances  in  all 
probability ;  the  absence  of  the  influence  of  the  nervous  sys- 
tem determining  the  variations  in  the  quantity  and  compo- 
sition of  the  outflow  of  the  secretions;  the  changes  in  the  rate 
of  soHsalled  absorption,  which  doubtless  influences  also  the  act 
of  the  secretion  of  the  juices— by  these  and  a  host  of  other  con- 
siderations we  are  lead  to  hesitate  before  we  commit  ourselves 
too  i^ireservedly  to  the  belief  that  the  processes  of  natural 
digmstion  can  be  exactly  imitated  in  the  laboratory. 

^piat  is  it  which  enables  oiie  man  to  digest  habitually  what 
may  be  almost  a  poison  to  another  P  How  is  it  that  each  one 
can  dispose  readily  of  a  food  at  one  time  that  at  another  is  quite 
indigestible  P  To  reply  that,  in  the  one  case,  the  digestive 
flidds  are  poured  out  and  in  the  other  not,  is  to  go  little  below 


imiiMiaiHinniii .'  a«lBiBi«*«iMinn.,jcgaBM 


i  itmmwwiwmLmv^^iwfflBa 


862 


ANIMAL  PHYSIOLOOT. 


r 


K 


|i 


the  surface,  for  one  asks  the  reason  of  this,  if  it  be  a  fact,  as  it 
no  doubt  is.  When  we  look  further  into  the  peculiarities  of 
digestion,  etc.,  we  recognize  the  influence  of  race  as  such,  and 
in  the  race  and  the  individual  that  obtrusive  though  ill-under- 
stood fact— the  force  of  habit,  operative  here  as  elsewhere. 
And  there  can  be  little  doubt  that  the  habits  of  a  people,  as  to 
food  eaten  and  digestive  peculiarities  established,  become  or- 
ganized, fixed,  and  transmitted  to  posterity. 

It  is  probably  in  this  way  that,  in  the  course  of  the  evolu- 
tion of  the  various  groups  of  animals,  they  have  coins  to  vary 
BO  much  in  their  choice  of  diet  and  in  their  digestive  prooocsoo, 
did  we  but  know  them  thoroughly  as  they  are;  for  to  assume 
that  even  the  digestion  of  mammals  can  be  summed  up  in  the 
simple  way  now  prevalent  seems  to  us  too  broad  an  assump- 
tion.   The  field  is  very  wide,  and  as  yet  but  little  explored^ 

Xuuui  nyiLdoKj.— -The  study  of  Alexis  St.  Martin  has  fur- 
nished probably  the  best  example  of  genuine  human  physiology 
to  be  found,  and  has  yielded  a  harvest  rich  in  results. 

We  suggest  to  the  student  that  self-observation,  without 
interfering  with  the  natural  processes,  may  lead  to  valuable 
knowledge ;  for,  though  it  may  lack"  some  of  the  precision  of 
laboratory  experiments,  it  will  prove  in  many  respects  more 
instructive,  suggestive,  and  impressive,  and  have  a  bearing  on 
medical  practice  that  will  make  it  telling.  Not  that  we  would 
be  understood  now  or  at  any  time  as  depreciating  laboratory 
experiments;  but  we  wish  to  point  out  from  time  to  time  how 
much  may  be  learned  in  ways  that  are  simple,  inexpensive, 
and  consume  but  little  time. 

The  lato  of  rh/yilhim,  is  illustrated,  both  in  health  and  disease, 
in  striking  ways  in  the  digestive  tract.  An  individual  long 
accustomed  to  eat  at  a  certain  hour  of  the  day  will  experience 
at  that  time  not  only  hunger,  but  other  sensations,  proi>ably 
referable  to  secretion  of  a  certain  quantity  of  th^  digestive 
juices  and  to  the  movements  that  usually  accompany  the  pres- 
ence of  food  in  the  alimentary  tract.  Some  persons  find  their 
digestion  disordered  by  a  change  in  the  hours  of  meals. 

It  is  well  known  that  defecation  at  periods  fixed,  even  within 
a  few  minutes,  has  become  an  established  habit  with  hosts  of 
people ;  and  the  same  is  to  a  degree  true  of  dogs,  ets.,  kept  in 
confinement,  that  are  taught  cleanly  habits,  and  encouraged 
therein  by  reg^ular  attention  to  their  needa 

Now  and  then  a  case  of  what  is  very  similar  to  regurgita- 
tion of  food  in  ruminants  is  to  be  found  among  human  beings. 


k  fact,  a8  it 
iliaritiesof 
1  sucli,  and 

I  ill-under- 
elsewhere. 
eople,  as  to 
become  or>- 

theevolu- 
lae  to  vary 
Bproceaaes, 
rtoaarame 
d  up  in  the 
axL  asaump- 
:plored« 
tin  has  fur- 
physiology 

on,  without 
to  valuable 
precision  of 
spects  more 
,  bearing  on 
Eit  we  would 
;  laboratory 
bo  time  how 
inexpensive, 

and  disease, 
ividual  long 

II  experience 
[18,  proi)ably 
h9  d^^tive 
my  the  pres- 
am  find  their 
leals. 

,  even  within 
rith  hosts  of 
et3.,  kept  in 
.  encouraged 

lio  regurgita- 
Lunan  beings. 


DIOBSTION  OF  FUOD. 


968 


This  is  traceable  to  habit,  which  is  bound  up  with  the  law  of 
rhythm  or  periodic  increased  and  diminished  activity. 

Indeed,  every  one  sufficiently  observant  may  notice  in  him- 
self instances  of  the  application  of  this  law  in  the  economy  of 
his  own  digestive  organs. 

This  tendency  is  important  in  preserving  energy  for  higher 
ends,  for  such  is  the  result  of  the  operation  of  this  law  every- 
where. , 

The  law  of  correlation,  or  mutual  dependence,  is  well  illus- , 
trated  in  the  series  of  organs  composing  the  alimentary  tract. 

The  condition  of  the  stomach  has  its  counterpart  in  the  rest 
of  the  tract :  thus,  when  St.  Martin  had  a  disordered  stomach, 
the  epithelium  of  his  tongue  showed  corresponding  changes. 

We  have  already  referred  to  the  fact  that  one  part  may  do 
extra  work  to  make  up  for  the  deficiencies  of  another. 

It  is  confidently  asserted  of  late  that,  in  the  case  of  persons 
long  unable  to  take  food  by  the  mouth,  nutritive  substances 
given  by  enemata  find  their  way  up  to  the  duodenum  by  anti- 
peristalsis.  Here,  then,  is  an  example  of  an  acquired  adaptive 
arrangement  under  the  stress  of  circumstances.    ' 

(It  can  not  be  too  much' impressed  on  the  mind  that  in  the 
complicated  body  of  the  mamnud  the  work  of  any  one  organ 
is  constantly  varying  with  the  changes  elsewhere.  It  is  this 
mutual  dependence  and  adaptation—an  old  doctrine,  too  much 
left  out  of  sight  in  modem  physiology — ^whioh  makes  the  at- 
tempt to  completely  unravel  vital  processes  well-nigh  hopeless ; 
though  each  accumulating  true  observation  gives  a  better  in- 
sight into  this  kaleidoscopic  mechanism. 

■  We  have  not  attempted  to  make  any  statements  as  to  the 
quantity  of  the  various  secretions  discharged..  This  is  large, 
doubtless,  but  much  is  probably  reabsorbed,  either  altered  or 
unaltered,  and  used  over  again.  In  the  case  of  ftatuU»  the  con- 
ditions are  so  unnatural  that  any  conclusions  as  to  the  normal 
quantity  from  the  data  they  afford  must  bejbighly  unsatisfac- 
tory. Moreover,  the  quantity  must  be  very  variable,  accord- 
ing to  the  law  we  are  now.  considering.  It  is  well  known  that 
dry  food  provokes  a  more  abundant  discharge  of  saliva,  and 
this  is  doubtless  but  one  example  of  many  other  relations  be- 
tween the  character  of  the  food  and  the  quantity  of  secretion 
provided.  ! 

■folvtlBB. — We  have  from  time  to  time  either  distinctly 
pointed  out  or  hinted  at  the  evolutionary  ioiplioations  of  the 
facts  of  this  department  of  physiology.    The  structure  of  the 


1 

I 


mm 


864 


ANIMAL  PHYSIOLOGY. 


ws 


■: 


digestive  organs,  plainly  indicating  a  rising  scale  of  complexity 
with  greater  and  greater  differentiation  of  function,  is,  beyond 
question,  an  evidence  of  evolution. 

The  law  of  natural  selection  and  the  law  of  adaptation, 
giving  rise  to  new  forms,  have  both  operated,  we  may  believe, 
from  what  can  be  observed  going  on  around  us  and  in  our- 
selves. The  occurrence  of  transitional  forms,  as  in  the  epi- 
thelium of  the  digestive  tract  of  the  frog,  is  also  in  harmony 
with  the  conception  of  a  progressive  evolution  of  structure 
and  function.  But  the  limits  of  space  will  not  permit  of  the 
enumeration  of  details. 

SnuMcy. — A  very  brief  risumi  of  the  subject  of  digestion 
will  probably  Bu^lce. 

Food  is  either  organic  or  inorganic  and  comprises  proteids, 
fats,  carbohydrates,  salts,  and  water ;  and  each  of  these  must 
enter  into  the  diet  of  all  known  animals.  They  must  also  be 
in  a  form  that  is  digestible.  Digestion  is  the  reduction  of  food 
to  a  form  such  that  it  may  be  further  dealt  with  by  the  aliment- 
ary tract  prior  to  bmng  introduced  into  the  blood  (absorption). 
Tbis  is  effected  in  different  parts  of  the  tract,  the  various  con- 
stituents of  food  being  differently  modified,  according  to  the 
secretions  there  provided,  etc.  The  digestive  juices  contain 
essentially  ferments  which  act  only  under  definite  conditions  of 
chemical  reaction,  temperature,  etc. 

@!he  dianges  wrought  in  the  food  are  the  following :  starches 
are  converted  into  sugars,  proteids  into  peptones,  and  fats  into 
fatty  acids,  soaps,  and  emulsion ;  which  alterations  are  effected 
by  ptyaUn  and  amylopmn,  pepsin  and  trypsin,  and  bile  and 
pancreatic  steapsin,  rs^wctively. 

Outside  the  mueous  membrane  mmtaining  the  glands  are 
muscular  ogats,  serving  to  bring  about  the  movements  of  the 
food  along  the  digestive  tract  and  to  expel  the  faces,  the.circu- 
lar  fibers  being  the  more  important  These  movements  and  the 
processes  of  secretion  and  so-called  absorption  are  under  the 
control  of  thenervous  system. 

The  preparation  of  the  digestive  secretions  involves  a  series 
of  changes  in  the  epithelial  cells  concerned,  which  can  be  dis- 
tinctly traced,  and  take  place  in  response  to  nervous  stimula- 
tion. 

These  we  regard  as  inseparably  bound  up  with  the  healthy 
life  of  the  cell.    To  be  natura),  it  must  secrete. 

The  blood-vessels  of  the  stomach  and  intestine  and  the  villi 
of  the  latter  receive  the  digested  food  for  further  elaboration 


III r riiiiyi'tftiV^r--mVil^lrilif^-- ^"''^-^■■ 


■^htim.  iiii'ik^mmigiijjjj^ 


complexity 
1,  is,  beyond 

adaptation, 
aay  believe, 
uad  in  our- 
in  the  epi- 
in  harmony 
»f  stracture 
jrmit  of  the 

of  digestion 

ses  proteids, 
'  these  must 
aust  also  be 
jtion  of  food 
thealiment- 
[absorption). 
various  con- 
rding  to  the 
ices  contain 
conditions  of 

ng:  starches 
Bad  fats  into 
1  are  effected 
ind  bile  and 

e  glands  are 
nneats  of  the 
les,  thedrcu- 
oents  and  the 
re  under  the 

elves  a  series 
;h  can  be  dis- 
^ous  stimula- 

h  the  healthy 

)  and  the  villi 
nr  elaboration 


80o 


ANIMAL  PHYSIOLOGY. 


thoracic  chamber  may  be  said  to  be  reserved  for  circulatory 
and  respiratory  organs  which,  we  again  point  out,  are  so  related 
that  they  really  form  parts  of  one  system. 

The  mammal's  blood  requires  so  much  a§ration  (ventilation) 
that  the  lungs  are  very  large  and  the  respiratory  system  has 
become  greatly  specialized.  We  no  longer  find  the  skin  or  ali- 
mentary canal  taking  any  large  share  in  the  process ;  and  the 
lungs  and  the  mechanisms  by  which  they  are  made  to  move  the 
gases  with  which  the  blood  and  tissues  are  concerned  become 
very  complicated. 


Ighniwry  . 


tr: 


Our  stupes  of  muscle  phyiidogy  should  have  made  clear 
the  fact  that  tissue-Ufe  impUes  the  comtant  consumption  of 
oxygen  and  discharge  of  carbtmio  anhydride,  and  that  the  pro- 
cesses which  give  raw  to  this  are  going  on  at  a  rapid  rate ;  so 
that  the  demands  of  tiie  animal  for  oxygen  constantly  may  be 
readily  understood  if  one  assumes,  what  can  be  shown,  though 
less  readily  than  iri  the  ca«e  of  muscle,  that  all  the  tissues  are 
constantly  craving,  as  it  were,  for  this  essential  oxygen— well 
called  "vital-ahf." 


IM»**IIH'!P'ti»V'»M»  ■ ' 


^■:*ie9iA  t^'4tW'«UtjM 


aMtj<^wuj<M»iWMi«(iii>i«*itM\i-»iatifcli 


i"e**»  ^  t^'^lMtt'l*"'^  t-r.-rv^.iffyV-'t.'KM^ 


I        I ) .Ill 


■^^■'^■■^•■■••^ii 


iinniiiwiiiinii»ii<m>. 


circtilatory 
e  BO  related 

rentilfttion) 
gystem  has 
gkin  or  ali- 
Msa;  and  the 
to  move  the 
med  become 


THE  BBSPIBATORT  SYSTEM. 


m 


vv  made  clear 
nuumption  of 
1  that  the  pro- 
rapid  rate ;  80 
itantly  may  be 
Ethowh,  though 
the  tiseaes  are 
[  oxygen— well 


Bespiratilm  may,  then,  be  regarded  from  a  physical  and 
chemical  point  of  view,  though  in  this  as  in  other  instances  we 


VM.  m.-' 


iteU  hM :  8,  diririM  to  aiddfe  lolw ;  a,  Sviiiaa  to  1^ 

orliiftimiflr:  ll,dlfWi»tolo««rlol»:  U,lt,ia;lil,«&iiMtoramlflairtfciMof  bnmdilft; 


U,U,  iM^tenta, 


in  oaatoar ;  14, 14,  mnintt  o(  liuiga ;  U,  U,  baaa  o(  taiaga. 


muAt  be  on  our  guard  against  rqpsrding  physiological  processes 
as  ever  purely  physical  or  purely  ohemicak  The  respiratory 
process  in  the  mammalj  unlUce  the  frog^  consists  of  an  active 
and  a  (largely)  passive  phase.  The  air  is  not  pumped  into  the 
lungs,  but  sucked  in.  So  great  is  the  coniplexity  of  the  lungs 
in  the:  mammal)  that  the  frog's  lung  (which  may  be  readily 
understood  by  blowing  it  up  by  inserting  a  small  pipe  in  the 
glottic  opening^of  the  animal  and  then  ligaturing  the  distended 
organ)  may  be  compared  to  a  single  infuudibulum  of  the  mam- 
malian lung. 

Assuming  that  the  student  is  somewhat  conversant  with  the 


868 


ANIMAL  PHYSIOLOGY. 


coarse  and  fine  anatomy  of  the  respiratory  organi,  we  call  at- 
tention to  the  physiological  aspects  of  some  points.  The  lungs 
represent  a  membranous  expansion  of  great  extent,  lined  with 
flattened  cells  and  supporting  innumerable  capillary  blood-ves- 
sels. The  air  is  admitted  to  the  complicated  foldings  of  this 
membrane  by  tubes  which  remain,  throughout  the  greater  part 
of  their  extent,  open,  being  oompoeed  of  cartilaginous  rings, 
completed  by  soft  tissues,  of  which  plain  muscle-oells  form  an 


Ftt.  aa-MoM  «(  m 


important  part,  serving  to  maintain  a  tonic  resistance  against 
pulmonary  and  bronchial  pressure,  as  well  as  serving  to  aid 
in  the  act  of  coughing,  ete.,  so  important  in  expellihg  foreign 
bodies  or  preventing  their  ingress. 

The  bronchial .iAbM  inre  lined  with  a  mucous  membrane, 
kept  moist  by  the  leeretionB  of  ito  i^Umds,  and  covered  with 
ciliated  epithelium,  as  are  also  the  nasal  passages,  irhich  by 
the  outward  currents  they  create,  favor  diffusion  of  gases,  and 
removal  of  excess  of  mucus.  The  thoracic  walls  and  the  lungs 
themselves  are  covered  with  a  tough  but  thin  membrane  lined 
with  flattened  cells,  which  secrete  a  small  quantity  of  fluid. 


Mwmwwfw  Biinwi 


we  call  at- 
The  lungs 
lined  with 
blood-vea- 
igs  of  this 
reaterpart 
ions  ringSy 
la  f  oim  aa 


Mr 


«v 


ince  against 
rving  to  aid 
ling  foreign 

I  membrane, 
iovered  with 
»,  frhich  by 
[>f  gases,  and 
nd  the  lungs 
nbrane  lined 
tity  of  fluid. 


THB  BESPIRATORT  SYSTEM. 


869 


that  serves  to  maintain  the  surrounding  parts  in  a  moist  con* 
dition,  thus  lessening  friction.    The  importance  of  this  ar- 


VMw  Mi-SMtim  of  Hm 
Mtai^iSdnilM). 


•,~a,~^«i  waSi  of  tiM  tkKOh ;  '!>,  imaa  i 


rangement  is  well  seen  when,  in  consequence  of  inflammation 
of  this  pleura,  it  becomes  dry,  giving  rise  during  each  respira- 
tory movement  to  a  friction-sound  and  a  painful  sensation. 
It  will  not  be  forgotten  that  this  membrane  extends  over  the 
diaphragm,  and  that,  in  consequence  of  the  lungs  completely 
filling  all  the  space  (not  occupi^  by  other  organs)  during  every 
position  of  the  chest-walls,  the  costal  and  pulmonary  pleural 
surfaces  are  in  constant  contact  By  far  the  greater  part  of 
the  lung-substance  consists  of  elastic  tissue,  thus  adapting  the 
principal  respiratory  organs  to  that  amount^of  distention  and 
recoil  to  which  they  are  ceaselessly  subjected  during  the  en- 
tire lifetime  of  the  animal. 

Thb  Entsaitcb  and  Exit  op  Air. 

Since  the  lungs  fill  up  so  completely  the  thoracic  cavity, 

manifestly  any  <^ange  in  the  sise  of  the  latter  must  lead  to 

an  increase  or  diminution  in  the  quantity  of  j^r  they  contain. 

Since  the  air  within  the  respiratory  organs  is  being  constantly 

M 


,j,^i^in«,,#«»iWfcTO*nw«. 


870 


ANIMAL  PHTSIOLOOT. 


robbed  of  its  oxygen,  and  rendered  impure  by  the  addition  of 
carbonic  dioxide,  the  former  must  be  renewed  and  the  latter 

expelled ;  and,  as  mere  diffu- 
sion takes  place  too  slowly  to 
accomplish  this  in  the  mam- 
mal, this  process  is  assisted 
by  the  nervous  system  set- 
ting certain  muscles  at  work 
to  alter  the  size  of  the  chest 
cavity.    Because  of  the  ribs 
being  placed  obliquely,  it  fol- 
lows that  their  elevation  will 
,  result  in  the  enlargement  of 
the  thoracic  cavity  in  the  au- 
tero-poeterior diameter;  and, 
as  the  chest,  in  consequetice, 
gets  widw  from  above  down- 
ward, also  in  the  transverse 
diameter;  which  is  more- 
over asristed  by  the  eversion 
of  the  lower  borders  of  the 
ribs;  and, if  the  convexity  of 
fhe  diaphragm  were  dimin- 
ished by  its  contraction  and 
consequent  descent,  it  would  follow  that  the  chest  would  be  in- 
creased in  the  vertical  diameter  also.    All  these  events,  favor- 
able to  the  entrance  of  air,  actuaUy  take  phice  through  agencies 
we  must  now  consider.    The  student  is  recommended  to  look 
into  the  insertion,  etcir  of  the  muscles  concerned,  to  which  we 
can  only  briefly  refer.  «      .        *  xv 

The  act  of  inspiration  commences  by  the  fixation  of  the 
uppermost  ribs,  beginning  with  the  first  two,  by  means  of  the 
soofent  muscles,  this  act  being  followed  up  by  the  contraction 
of  the  external  interoostals,  leading  to  the  elevation  of  the 
other  ribs;  at  the  same  time,  the  arch  of  the  diaphregm  de- 
scends in  consequence  of  the  contraction  of  its  various  mus- 
cular bundles.  Under  these  circumstances,  the  air  from  with- 
out must  rush  in,  or  a  vacuum  be  formed  in  the  thoracic 
cavity ;  and,  since  there  is  free  access  for  the  air  through  tiie 
glottic  opening,  the  lungs  are  of  necessity  expanded.  This  in- 
going air  has  had  to  overcome  the  elastic  resistance  of  the 
lungs,  which  amounts  to  about  5  millimetres  of  mercury  in 
man,  as  ascertained  by  tying  a  manometer  in  the  windpipe  of 


■  'V^JBiWiBBMWWffl 


im)!<ww»a'^*wWJ'^  •i^ummi^yimi^ki^vm^^i'^^''^^ 


addition  of 
1  the  latter 
.  mere  diffu- 
loo  slowly  to 
in  the  mam> 
I  is  assisted 
system  set- 
cles  at  work 
of  the  chest 
)  of  the  ribs 
iquely,itfol- 
levation  will 
argement  of 
ityintheau- 
uneter;  and, 
consequetice, 
above  down- 
le  transverse 
oh  is  more- 
the  evendon 
>rder8  of  the 
convexity  of 
were  dimin- 
itraction  and 
would  be  in- 
ivents,  f avor- 
>ngh  agencies 
inded  to  look 
,  to  which  we 

ntion  of  the 
means  of  the 
le  contraction 
ration  of  the 
iaphragm  de- 
various  mus- 
dr  from  with- 
the  thoracic 
T  through  the 
ded.  This  in- 
stance of  the 
)f  mercury  in 
le  windpipe  of 


THE  BBSPIRATORT  STSTBM. 


Wl 


a  dead  subject,  and  then  opening  the  thorax  to  equalize  the 
inside  and  outside  pressures,  when  the  lungs  at  once  collapse 
and  the  manometer  shows  a 
rise  of  the  mercury  to  the  ex- 
tent indicated  abova  To  this 
we  must  add  the  influence  of 
the  tonic  contraction  of  the 
bronchial  muscles  before  re- 
ferred to,  though  this  is  prob- 
ably not  very  great 

That  there  are  variations 
of  intrapulmonary  pressure 
may  be  ascertained  by  con- 
necting a  manometer  with  one 
nostril — the  other  being  closed 
—or  with  the  windpipe.  The 
mercury  shows  a  negative 
pressure  with  each  inspirato- 
ry, and  a  positive  with  each 
expiratory  act  This  may 
amount  to  from  30  to  70  mil- 
limetres with  strong  inspira- 
tion, and  60  to  100  in  forcible 
expiration. 

When  inspiration  ceases,  the  elastic  recoil  of  the  rib  carti- 
lages and  the  ribs  themselves,  and  of  the  sternum,  the  weight 


Vm-  3m. -pifimmiiutie  wpwwirtaUiMi  of 
mMw  ttjmwknmm  in  ianinaiM  (Om- 
5f^)-_.^?i?^  *SSf<^  thnmgh  moomI 
AoailKUMto.   The  brokwiMHl  dotted 

*-— theMMutarttodaMntaftto 

to  ofdioMy  and  la  dev  iMvIm- 


■I  1  -T  ■%  ^■■^*'-wr''Vg'™«<  '^vv>'' 


iff'T!SS.^2J!5*ff*»  '38*^52.2'  Wn^thorMlo  Mid  eztemia 
MitulMflMrttrt£«iM£ofaiMltebMM«nM^^ 


tiiaMawewMl;  teri|lit< 
At  OM  part  (8)  an  •laMciaii 


InagB.  The 
OMrcutT 
(.Jar.   laMt-L^ 
■  tlwajttMiial^ 
I  a  hole  in  Jar, 


(attar 
ahrandi- 
ofttMjariB 


itwOlbe 


■*r.  '-'rr~^~-^''^fr-'if^>^.^^-i^*^^'fi^^(imiitiii..i<'r"»^^ 


873 


AKIMAL  PUYSIOLOOT. 


fto.  aOB.— Donal  vtew  oC  four  wMfM 

•«•«>«"»«*  »'_^«ft*.  52''tt2 
torn  MMl  tatoworti*  (SCS  *££ 

ton :  % f xtarwUliitMvartal :  t, in- 


of  these  parts  and  that  of  the  attached  nmwles.  etc.,  awiBts  to 
the  return  of  the  chest  to  its  original  position,  entirely  indepen- 

dently  of  the  action  of  muscles. 
Moreover,  with  the  descent  of  the 
diaphragm  the  abdominal  viscera 
have  been  thrust  down  and  com- 
pressed together  with  their  mcluded 
gases;  when  this  muscle  relaxes, 
they  naturally  exert  an  upward 
pressure.     Putting    these    events 
together,  it  is  not  difficult  to  un- 
derstand why  the  air  should   be 
squeeaed  out  of  the  lungs,  the  elas- 
ticity of  which  latter  is,  as  we  have 
shown,  an  important  factor  in  itself. 
Tha  MvsdM  of  BMpintira^The 
diaphragm  may  be  considered  the 
most  important  single  respiratory 
muscle,  and  can  of  itself  maintain 

respiration.    The  »odUni  are  important  as  fixators  of  the  ribs ; 

the  levalores  eostartm,  and  exUnud  irUercosUds,  as  normal  eie- 

vators.     The    quadrahu   himborum 

Assists  the  diaphragm  by  fixing  the 

last  rib.    These,  with  the  serraiua 

portieua  superior,  may  be  regarded 

as  the  principal  muscles  called  into 

action   in  an  ordinary  inspiration. 

The  muscles  used  in  an  ordinary  ex- 
piratory act  are  the  internal  iniercoa- 

tola,  the  trtaingvlaria  demi,  and  ser- 

ratits  poaiieu8  inferior.     In  forced 

inspiration  the  lower  ribs  are  drawn 

down  and  retracted,  giving  support 

in   their  fixed   position  to  the  dia- 
phragm.     The    scaleni,    pectorales, 

serratus   magnus,  latissimus   dorsi, 

and  others  are  called  into  action ;  but 

when  dyspnoea  becomes  extreme,  as 

in  one  with  a  fit  of  asthma,  nearly  all 

the  muscles  of  the  body  may  be  called 

into  play,  even  the  muscles  of  the 

face,  which  are  not  normally  active  at  all  or  but  very  shghtly 

m  natural  breathing. 


'oSSr'QiukiiiMd 


nSSSS  InthtoeMetlMitaia 
•tiaa  to  aUMidtd  with  <"*■ 


THE  RBSPIBATORT  SYSTBlL 


878 


;.,  assists  in 
ily  indepen- 
)f  muscles, 
cent  of  the 
nal  viscera 
1  and  com- 
eir  included 
icle  relaxes, 
an  upward 
lese  events 
Icult  to  un- 

should  be 
igs,  the  elas- 
I,  as  we  have 
ctor  in  itself. 
IntiMk— The 
osidered  the 

respiratory 
elf  maintain 
I  of  the  ribs; 
I  normal  ele* 


^(•ftarQnikiiiMd 
I.  iuTBZ  taqoM 
n.  DniW^deMiin- 
Iwaaad  ooamwner- 
idilwvvWble.  Soeb 
tt  PHiMMft  in  iBMV 

MWlBWllldl 

ndtdwtth"' 


Faeial  and  laryngeal  reapiraiion  is  best  seen  in  such  animals 
as  the  rabbit,  auii  it  is  this  condition  which  is  approximated 
in  disordered  states  in  man — in  fact,  when  from  any  cause  in> 
spiration  is  very  labored  (aHthma,  diphtheria,  etc.). 

In  man  and  most  mammals,  unlike  the  frog,  the  glottic 
opening  is  never  entirely  closed  during  any  part  of  the  respira- 
tory act,  though  it  undergoes  a  rhythmical  change  of  size, 
widening  during  inspiration  and  narrowing  during  expiration, 
in  accordance  with  the  action  of  the  muscles  attached  to  the 
arytenoid  cartilages,  the  action  of  which  may  be  studied  in 
man  by  means  of  the  laryngoscope. 

The  abdominal  muscles  have  a  powerful  rhythmical  action 
during  forced  respiration,  though  whether  they  function  dur- 
ing ordinary  quiet  breathing  is  undetermined ;  if  at  all,  prob- 
ably but  slightly.  Though  the  removal  of  the  external  inter- 
costab  in  the  dog  and  some  other  animals  revMtls  the  fact  that 
the  internal  intercostals  contract  alternately  with  the  dia- 
phragm, it  must  not  be  regarded  as  absolutely  certain  that  such 
is  their  action  when  their  companion  miiscles  are  present,  for 
Nature  has  more  ways  than  one  of  accomplishing  the  same  pur- 
pose—a fact  that  seems  oftdn  to  be  fprgotten  in  reasoning  from 
experiments.    This  result,  however,  carries  some  weight  with  it. 

Types  of  Xsspintiioiii.— There  are  among  mammals  two  princi- 
pal types  of  breathing  recognizable — ^the  costal  (thoracic)  and 
abdominal — ^according  as  the  movements  of  the  chest  or  the 
abdomen  are  the  more  pronounced. 

In  the  civilized  white  woman,  even  in  the  female  child,  the 
upper  thorax  takes  a  larger  share  in  respiration  than  in  the 
male  sex.  This  has  been  explained,  on  the  one  hand,  as  being 
due  to  artificial  influences,  modes  of  dress,  and  their  inherited 
effects ;  and  on  the  other  to  natural  ones,  the  crowding  of  the 
respiratory  organs,  owing  to  the  contents  of  the  pelvio  and 
abdominal  cavities  encroaching  on  the  thorax,  in  consequence 
of  the  enlargement  of  the  uterus  during  pregnancy.  It  has, 
however,  been  maintained  recently  that  an  examination  of 
pure-blooded  Indian  girls  does  not  show  the  features  of  respira- 
tion just  noticed  as  characteristic  of  the  breathing  of  white 
females,  the  inference  from  which  is  obvious.  But,  again,  it  i8> 
to  be  remembered  that  the  Indian  and  other  women  retaining^ 
primitive  habits  possess  a  power  of  adaptation  to  the  demands  | 
of  the  pregnant  condition  no  longer  shown  by  white  women. 
Thoracic  breathing  in  females  is  probably  the  result  of  several 
co-operating  causey  of  which  xtmge  in  dress  is  on& 


-, 


■iwgww  wMmmi  lui  -wi'i  J.>^miwwi.i 


874 


ANIMAL  PHYSIOLOOT. 


PMNMnal  ObMTfKkioB.— The  student  would  do  well  at  this  stage 
to  test  the  t  itements  we  have  made  in  regard  to  the  respira- 
tory movemems  on  the  human  subject  especially.  This  he 
can  very  well  do  in  his  own  person  when  stripped  to  the  waist 
before  a  mirror.  Many  of  the  abnormalities  of  the  forced  res- 
piration of  disease  may  be  imitated— in  fact,  this  is  one  of  the 
departments  of  physiology  in  which  the  human  aspects  may 
be  examined  into  by  a  species  of  experiment  on  one's  self  that 
is  as  simple  as  it  is  valuable. 


tm.  m.~Fnt¥la  Omteri,  m  aaitea  uuMHdllflM  in  • 


teftarHuainr).  th* out mmMMi thaw 
firam  tta  oalaareoai  tiba.  a,  braaohlal 
hood-Un 


9,  OfB. 


(hinB«teiMU»«)«sMM«i 

tiba.   a,  braaohlal  (TMplntotT)  phUBM,  tJhmuiuiUf  mmuw  ;  o, 
ai  vtHiorMdofmjr;  e,iM«w;  il,itoaMah  ;«,«»■; /,liM«{ 


HMMMHMNMHlMkMWi 


t  this  stage 
he  respira- 
'.  This  lie 
X)  the  waist 
forced  res- 
one  -of  the 
spects  may 
i'B  self  that 


THE  BBSPIRATOBT  SYSTEM. 


878 


Ito.  SOB. 


no.  m. 


rm.  «IS.-Vertioia  tnuiwrane  mcUoh  oT  (MribwitMr  miMHl  (^MdoH)  ttooo;^  hevt  (^ter 
HnzlaTi.    r,  ««ntriale:  ii.  auriolM:  r,  nelam;  js  pwlowdim:  <,  fmiw,  «,  o^ 

lnf«»in*fcm(altSirBiiSC    A,  bwwdilri  Mtwy ;  ^.  hrMnJ^MBliiwMi  faowiecUoB ; 

0«BVMWttft.~It  is  hoped  that  the  various  figures  accompa- 
nied by  descriptions^  introduced  in  this  and  other  chapters,  will 
make  the  relations  of  the  circulation  and  respiration  in  the  va- 


-w-— 


iMim»iwi'  il>»ii>i»i»«H''»'' 


r>«M 


876 


ANIMAL  PHYSIOLOGY. 


rious  classes  of  animals,  whether  terrestrial  or  aquatic,  evident 
without  extended  treatment  of  the  subject  in  the  text.    What 


w& 


rNktM. 


Fw.aoQ. 


Fm, 


we  are  desirous  of  impreiasing  is  that  throughout  the  entire  ani- 
mal kingdom  respiration  is  essentially  the  same  process;  that 


r».  ni.- 


0.  Hoiv 


finally  it  resolves  itself  into  tisarue-brcathing :  the  appropria- 
tion of  oxygen  and  the  excretion  of  carbon  dioxide.  Since  the 
manner  in  which  oxygen  is  introduced  into  the  lungt  ^d  foul 
gases  expelled  from  them  in  some  reptiles  and  amphibiaas,  is 
krgely  different  from  the  method  of  respiration  in  the  mam- 
mal, we  call  attention  to  this  process  in  an  animal  readily 
watched— the  common  frog.  This  creature,  by  depressing  the 
floor  of  the  mouth,  enlarges  l^s  air-spaoe  in  this  region  and 
consequently  the  air  freely  enters  through  the  nostrils;  wher^ 
upon  the  latter  are  dosed  by  a  sort  of  valve,  the  glottis  opened 


MMM 


liilmMiiwiiiiwWi 


ic.  evident 
rt.    What 


M.tia 


tier  BlanohArd). 
er  Ducta).   pm. 


)  entire  ani- 
ocess;  that 


I  mm:  a,an;  o, 

«Mhka«|iMrtara. 
■  rli^iMSMdoC 


I  appropna- 
b  Since  the 
tgs  imd  foul 
ipbibiaiui,  is 
n  the  mam- 
mal readily 
[iresBing  the 
region  and 
rili;  irhere- 
ottiii  opened 


THE  RBSPIRATOBY  SYSTEM. 


877 


and  the  air  forced  into  the  lungs  by  the  elevation  of  the  floor 
of  the  mouth.  By  a  series  of  flank  movements  the  elasticity 
of  the  lungs  is  aided  in  expelling  the  air  tl^rough  the  now  open 
nostrils.  The  respiration  of  the  turtle  and  some  other  reptiles 
is  somewhat  similar.    In  the  case  of  aquatic  animals^  both  in- 


W».  Wi.-q<atwlTteirot«lrrtMr»olw<it<ii^<»w»d  mmMtf^  ■lyth»»wl>ttewi"yMi 
BrlMlBal«teM»(i(tnuikOrfl|rSWMr)-   l.l.aflMwrtwinlhraCcirTloainMr?iiiwn 


Mth 


vertebrate  and  vertebrate,  excepting  mammals,  the  blood  is 
freely  exposed  in  the  gillt  to  oxygen  dissolved  in  the  water  as 
it  is  to  the  same  gas  mixed  with  nitrogen  in  terrestrial  animals. 
In  the  land-snail,  land-crab,  etc.,  we  Imve  a  sort  of  intermedi- 
ate condition,  the  gills  being  kept  moist    It  is  not  to  be  for- 


878 


ANIMAL  PHTSIOLOGT. 


gotten,  however,  that  normally  the  respiratory  tract  of  mam- 
mals  is  never  other  than  slightly  moist. 


Thb  Quantitt  of  Ant  bkspibbd. 

We  distinguish  hetween  the  quantity  of  air  that  usually  is 
moved  by  the  thorax,  and  that  which  may  be  respired  under 
special  effort,  which,  of  course,  can  never  exceed  the  capacity 
of  the  respiratory  organs. 

Accordingly,  we  recognise:  1.  Tidal  air,  or  that  which 
passes  in  and  out  of  the  respiratory  passages  in  ordinary  quiet 
breathing,  amounting  to  about  500  cc.,  or  thirty  cubic  inches. 
2.  Complemenial  air,  which  may  be  voluntarily  inhaled  by  a 
forced  inspiration  in  addition  to  the  tidal  air,  amounting  to 
1,600  cc,  or  about  100  cubic  inches.  3.  SupplemerUal  {reserve) 
air,  which  may  be  expelled  at  the  end  of  a  normal  respiration 
— ^L  e.,  after  the  expulsion  of  the  tidal  air,  and  ifhich  represents 
the  quantity  usually  left  in  the  lungs  after  a  normal  quiet 
expiration,  amounting  to  1,500  cc.  4.  Reaiduai  atr,,  which  can 
not  be  voluntarily  expelled  at  all,  amounting  to  about  2,000  cc, 
or  120  cubic  inches. 

The  vital  capacity  is  estimated  by  the  quantity  of  air  that 
may  be  expired  after  the  most  forcible  inspiration.  This  will, 
of  course,  vary  with  the  age,  which  determines  largely  the  elas- 
ticity of  the  thorax,  together  with  sex,  position,  height,  and  a 
variety  of  other  circumstiuioes.  But,  inasmuch  as  the  result 
may  be  greatly  modified  by  practice,  like  the  power  to  expand 
the  chest,  the  vit^l  capacity  is  not  so  valuable  an  indication  as 
might  at  first  be  supposed. 

It  is  important  to  bear  in  mind  that  the  tidal  air  is  scarcely 
more  than  snfficient  to  fill  the  upper  air-passages  and  larger 
bronchi,  so  that  it  reqtures  from  five  to  ten  respirations  to  re- 
move a  quantity  of  air  inspired  by  tai  ordinary  Act.  Very 
much  muft,  therefore,  depend  on  diffusion,  the  quantity  of  air 
remaining  in  the  lungs  after  each  breath  being  the  sum  of  the 
residual  and  reserve  air,  or  about  8,500  oc.  (890  cubic  inches). 
Oonsidering  the  creeping  slowness  of  the  capillary  dronlation, 
it  would  not  be  supposed  that  the  respiratory  process  in  its 
essential  parts  shotdd  be  the  nipid  one  that  a  greater  move* 
ment  of  the  air  would  imply. 


ma 


of  mam- 


luaaUy  is 
ired  under 
e  capacity 

bat  wbicli 
nary  quiet 
ibic  inches, 
laled  by  a 
jonting  to 
al  {reserve) 
respiration 
.  represents 
rmal  quiet 
..which  can 
at  2,000  cc, 

of  air  that 
This  will, 
)ly  the  elas- 
>ight,  and  a 
I  the  result 
r  to  expand 
idioation  as 

r  is  scarcely 
and  larger 
ktions  to  re> 
*ot.  Very 
intityofair 
I  sum  of  the 
bio  inches), 
cirenlation, 
rooess  in  its 
eater  move* 


THB  BBSPIBATORY  ST8TSM. 


Thb  Rkspibatoby  Rhtthm. 


879 


In  man,  and  most  of  our  domestic  mammals,  a  definite  rela- 
tion between  the  cardiac  and  respiratory  movements  obtains, 
there  being  about  four  to  five  heart-beats  to  one  respiration, 
which  would  make  the  rate  of  breathing  in  man  about  sixteen 
to  eighteen  per  minute.  Usually,  of  course,  the  largest  animab 
have  the  slower  pulse  and  respiration;  and  this  is  an  invariable 
rale  for  the  varieties  of  a  species,  as  observable  in  the  canine 
race,  to  mention  a  well-known  instance. 

The  rate  uf  the  respiratory  movements  is  to  some  extent  a 
measure  of  the  ntpidity  of  the  oxidative  processes  in  the  body, 
as  witness  the  slow  and  intermittent  breathing  of  cold-bloodeid 
animals  as  compared  with  the  more  rapid  respiration  of  birds 
and  mammals  (Fig.  313). 

Palhiologiesl. — ^Any  condition  that  lessens  the  amount  of  re- 
spiratory surface,  or  diminishes  the  mobility  of  the  chest-walls 
is  usually  accompanied  by  accelerated  movements,  but  beneath 
this  is  the  demand  for  oxygen,  part  of  the  avenues  by  which 
this  gas  usually  enters,  having  been  dosed  or  obsirnoted  by  the 
disease.  So  that  it  is  not'  suxprising  that,  in  consequence  of 
the  effusion  of  fluid  into  the  thoracic  cavity,  leading  to  the 
compression  of  the  lung,  the  oppodte  one  should  be  called  into 
more  frequent  use,  and  even  enlarge  to  meet  the  'demand. 
These  facts  show  how  urgent  is  the  need  for  constant  ventila- 
tion of  the  blood,  and  at  the  same  time  how  great  is  the  power 
of  adaptation  to  meet  the  emeigency. 

The  difference  between  the  inq»iratory  and  the  expiratory 
rhythm  may  be  gathered  by  watching  the  movements  of  the 
bared  chest,  or  more  accurately  from  a  graphic  record.  It  is 
usually  considwed  that  expiration  is  only  tUghtly  longer  than 
inspiration,  and  ttiat  any  marked  deviation  from  this  relation 
should  arouse  suspicion  of  disease.  Normally  the  respiratory 
pause  is  very  slight,  so  that  inspiration  seems  to  follow  di- 
rectly on  expiration ;  though  the  latter  act  reminds  us  of  the 
prolongation  of  the  ventricular  systole  after  the  blood  is  ex- 
pelled. 

If,  in  the  tracing,  the  small  waves  on  the  upper  part  of  the 
expiratory  curve  really  represent  the  effect  of  the  heart-beat,  it 
makes  it  easier  to  understand  how  such  might  assist  in  venti- 
lating the  blood  when  the  respirations  occur  only  once  in  a 
considerable  interval  and  very  feebly  then,  as  in  hibernating 
animals  or  individuals  that  have  fainted ;  though  it  must  be 


880 


ANIMAL  PHYSIOLOGY. 


remembered  that  diffusion  is  a  ceaseless  process  in  all  Hving 
vertebrates. 

It  is  scarcely  necessary  to  point  out  that  the  respiratory 


-rAA/-^AAr 


WlAA/l/WVUia 

0mmM0mmnfum\j\S)imm^ 


■hiUow,  MMl  in  ml  (IMP- 


movements  are  increased  by  exercise,  emotions,  position,  sea- 
son, hour  of  the  day,  taking  meals,  etc. 


mammm 


l,)ltfMMIt»MtHiMKHmit 


all  liying 
aspiratory 

/XT 


^A/1 


ifWW 


groups  of 


KMsition, 


THB  RBSPIBATORT  STSTBM. 


881 


^fK^^^/^J\^r^f^rJA/^^^\N'^VA^ 


Wm.  S14.—Tnoiiigt  of  ni|riratlMo(kan»iHiM  at  iMt  and  after  ezeroin  (•Iter  ThMriMOtor). 
/,  iMpiration ;  Ji;  caanntiaii.  8|«eaa  bstwaen  vertloal  HnM  indioata  tUM  Mcioili  ot  oiw 
aeoondea*^  1,  aimial  atandhn  at  rwt;  1.  alter  walk  at  IWr  mlnntaa;  7  and  ft  attet 
trottiiis;  •,  afterabrinf  rcat:  U,  after  trotting  and  nmntaig  (oraomeminiitaa;  17,aftw 
nattngfKnnlaitforadMcttiiM;  »1,  tradiig  at  awd  ot  eKpanmant. 

Bai^ntorj  Saniidiy— The  entrance  and  exit  of  air  are  accom- 
panied by  certain  sounds,  which  vary  with  each  part  of  the 
respiratory  tract.  To  these  sonnds  names  have  been  given,  but 
as  they  are  sqmewhat  inconstant  in  their  application,  or  at  least 
have  several  sjrnonyms,  we  paw  them  by,  recommending  the 
student  to  actually  learn  the  nature  of  the  respiratory  murmurs 
by  listening  to  the  normal  chest  in  both  man  and  the  lower  ani- 
mals. With  the  use  of  a  douUe  stethoscope  he  may  practice  upon 
himself,  though  not  so  advantageously  as  in  fhe  case  of  the  heart. 

The  sounds  are  caused  in  part  by  the  friction  of  the  air, 
though  they  are  probably  complex,  several  factors  entering  into 
their  causation. 

Comparison  of  thb  Inbpirbd  and  Expirbd  Ant. 

The  changes  that  take  place  in  the  air  respired  may  be 
briefly  stated  as  follows : 


888 


ANIMAL  PHYSIOLOGY. 


y 


- 1.  Whatever  the  condition  of  the  inspired  air,  that  expired 
is  about  saturated  with  aqueous  vapor — ^i.  e.,  it  contains  all  that 
it  is  capable  of  holding  at  the  existing  temperature. 

2.  The  temperature  of  the  expired  air  is  about  that  of  the 
blood  itself,  so  that  if  the  air  is  very  cold  when  breathed,  the 
body  loses  a  great  deal  of  its  heat  in  warming  it.  The  expired 
air  of  the  nasal  passages  is  slightly  warmer  than  that  of  the 
mouth. 

3.  Experiment  shows  that  the  expired  air  is  really  dimin- 
ished in  volume  to  the  extent  of  from  one  fortieth  to  one  fiftieth 
of  the  whole.  Since  two  volumes  of  carbonic  anhydride  require 
for  their  composition  two  volumes  of  oxygen,  if  the  amount  of 
the  former  gas  expired  be  not  equal  to  the  amount  of  oxygen 
inspired,  some  of  the  latter  must  have  been  tised  to  form  other 

combinations.    -^,  amounting  to  rather  less  than  1,  is  called 

the  respiratory  coefficient. 

4.  liie  ^fference  between  inspired  and  expired  air  may  be 
gathered  from  the  following : 

OsTgm.  mtroiHi.       Ovbonle  dknlde. 

V         luvinddf -. aO«10  79-180  (HMO 

Bxpii^air 1«<»8  79-897  4-880 

From  which  the  most  important  conclusions  to  be  drawn 
are,  that  the  expired  air  is  poorer  in  oxygen  to  the  extent  of 
4  to  5  per  cent,  and  richer  in  carbonic  anhydride  to  somewhat 
leas  tham  this  amount. 

From  experiment  it  has  been  ascertained  that  the  amount 
of  carbonic  dioxide  is  for  the  average  man  800  grammes  (406 
litres,  equivalent  to  218*1  grammes  carbon)  daily,  the  oxygen 
actuijly  used  for  the  same  period  being  700  grammes.  But 
the  variations  in  such  cases  are  veiry  great,  so  that  these  num- 
bers must  not  be  interpreted  too  rigidly.  Ibqierience  proves 
that,  while  chemists  often  work  in  laboratories  in  which  the 
percentage  of  carbonic  anhydride  (from  chemical  decomposi- 
tions) reaches  6  per  cent,  an  ordinary  room  in  which  theafnount 
of  this  gas  reaches  1  per  cent  is  entirely  unfit  for  occupation. 
This  is  not  because  of  the  amount  of  the  parbon  dioxide  pres- 
ent, but  of  other  impurities  which  seem  to  be  excreted  in  pro- 
portion to  the  amount  of  this  gas,  so  that  the  latter  may  be 
taken  as  a  measure  of  these  poisona 

What  these  are  is  as  yet  almost  entirely  unknown,  buir  ti»t 
they  are  poisons  is  beyond  doubt.    Small  effete  particles  oi 


iiii)rtiiiiiMfciii«i4t^w 


lat  expired 
ins  all  that 

;hat  of  the 
eaihed,  the 
Ixe  expired 
that  of  the 

ally  dimin- 
one  fiftieth 
ride  require 
I  amount  of 
of  oxygen 
form  other 

1,  is  called 


air  may  be 


}Mbaiiledii»>d«. 
(HMO 
4-880 

y  be  drawn 
le  extent  of 

0  somewhat 

the  amount 
ammes  (406 
the  oxygen 
mmes.  But 
these  num- 
ence  proves 

1  which  the 
decomposi- 
theatnount 
occupation. 

lioxide  pres- 
■eted  inpro- 
tter  may  be 

^ft,bat  tiiat 
particles  of 


THE  BESPIRATOBT  STSTBM. 


888 


onoe-living  protoplasm  are  carried  out  with  the  breath,  but 
these  other  substances  are  got  rid  of  from  the  blood  by  a  vital 
process  of  secretion  (excretion),  we  must  believe;  which  shows 
that  the  lungs  to  some  degree  play  the  part  of  gls  ' ',  and  that 
their  whole  action  is  not  to  be  explained  as  if  they  «  ^re  merely 
moistened  bladders  acting  in  accordance  with  ordinary  physical 
law& 

'  An  estimation  of  the  amount  of  atmospheric  air  required 
may  be  calculated  from  data  already  given. 

Thus,  assuming  that  a  man  gives  up  at  each  breath  4  per 
cent  of  carbon  dioxide  to  the  SOO  co.  of  tidal  air  he  expiree,  and 
breathes,  say,  seventeen  times  a  minute,  we  get  for  the  amount 
of  air  thus  charged  in  one  hour  to  the  extent  of  1  i>er  cent : 

SOO  X  4  X  17  X  60  s  3,040,000  cc.,  or  2,040  litres. 

But  if  the  air  is  to  be  contaminated  to  the  extent  of  only 
^  per  cent  of  carbonic  anhydride,  the  amount  should  equal  at 
least  8,040  X  10  hourly. 

Rkspibatiok  in  thb  Blood. 

It  may  be  noticed  that  arterial  blood  kept  in  a  confined 
space  grows  gradually  darkey  in  color,  and  that  the  original 
bright  scarlet  hue  may  be  restored  by  shaking  it  up  with  air. 
When  the  blood  has  passed  through  the  capillaries  and  reached 
the  veins,  the  color  has  changed  to  a  sort  of  purple,  character- 
istic of  venous  blood.  Putting  these  two  facts  toge^er,  we  are 
led  to  suspect  that  the  change  has  been  caused  in  some  way  by 
oxygen.  Exact  experiments  with  an  appropriate  form  of  blood- 
pump  show  that  from  one  hundred  volumes  of  blood,  whether 
arterial  or  venous,  about  sixty  volumes  of  gas  may  be  obtained ; 
that  this  gas  consists  chiefiy  of  oxygen  and  carbonic  anhydride, 
but  that  the  proportions  of  each  present  depends  upon  whether 
the  blood  is  arterial  or  venous. 

The  following  table  will  make  this  clear  r 


ArterUblood. 
Venoiu  UoocL. 


OUIM. 

OHlM)iiieulv<iU«- 

mtiDtm 

M 

40 

1-8 

»-lt 

46 

1-4 

from  100  volumes  of  blood  at  0*  0.  and  760  millimetre  pressure. 

Arterial  blood,  then,  contains  8  to  IS  per  cent  more  oxygen 

and  about  6  per  cent  more  carbonic  dioxide  than  venous  blood. 

It  is  not,  of  course,  true,  as  is  sometimes  supposed,  that  arterial 


4 


.t 


/ 


884 


ANIMAL  PHYSIOLOGY. 


blood  is  "  pure  blood  **  in  the  sense  that  it  contains  no  carbbnic 
anhydride,  as  in  reality  it  always  carries  a  large  percentage  of 
this  gas. 


Fm.  sib.— DtagnuuiMtie 
TeSmlV     A  to  tartly 

B*  tola  turn  niMd 
Ukd  witta  BMNwr.  Mtaam  pyiuuMy  m  *  **«  ft[|T«  •«* 
te  d  and  kHrar&R  B*,  tlM  lAal^  tte  MMtcnrr  te^^^ 

imrartait i.'. •  «MniimS«iBitor||r tmMminA  tuAmuAtnllbm tmSUim l>«tw»wi ^ud  A 
I(tS?Mok  i  bJiSi?^i*iS^g^«  otttabloodhiOwMiWteto  «>» JS™"^  ;i,*»« 

(AfMrlVMlMr.) 


thnmi^*. 


TlMOoadttiflniiBd«r«Uidi  tli*  0mm  cdH  ia  th«  BlMd.— If  a 
flaid,  as  water,  be  exposed  to  a  mixture  of  gases  whicli  it  cm 


LO  caTb6iuc 
rcentage  of 


i  mad  B  v?**** 
of  tiw  aloiHiock 

NlJdwOOIUIMtM 

Mreanr.  aad  tlie 

10  oil*  tBffWll^  6* 

'iaiatuninind 
iMtaMt  drivw  ool 

fMunmoCilanl 
i|trMai«M*«i 


— If  » 

hich  it  <Mm 


THE  BBSPIRATORY  SYSTEM, 


8f 


absorb  under  pressure,  it  is  found  that  the  amouiti  taken  n^ 
depends  on  the  quantity  of  the  particular  gas  present  independ- 
ent of  the  presence  or  quantity  of  the  others ;  thus,  if  water 
be  exposed  to  a  mixture  of  oxygen  and  nitrogen,  the  quantity 
of  oxygen  absorbed  will  be  the  same  as  if  no  nitrogen  were 
present— i  e.,  the  absorption  of  a  gas  varies  with  the  partial 
preasure  of  that  gas  in  the  atmosphere  to  which  it  is  exposed. 
But  whether  blood,  deprived  of  its  gases,  be  thus  exposed  to 
oxygen  under  pressure,  or  whether  the  attempt  be  made  to 
remove  this  gas  from  arterial  blood,  it  is  found  that  the  above- 
stated  law  does  not  apply. 

When  blood  is  placed  under  the  exhaustion-pump,  at  first 
very  little  oxygen  is  given  off ;  then,  when  the  pressure  is  con- 
siderably reduced,  the  gas  is  suddenly  libwated  in  large  quan- 
tity, and  after  this  comparatively  little.  A  precisely  analogoifti 
course  of  events  takes  place  when  blood  deprived  of  its  oxygen 
is  submitted  to  this  gas  under  pressure.  On  the  other  hand, 
if  these  experiments  be  made  with  serwn,  absorption  follows 
according  to  the  law  of  pressures.  Evidently,  then,  if  the  oxy- 
gen is  merely  dissolved  in  the  blood,  such  solution  is  peculiar, 
and  we  shall  presently  see  that  this  supposition  is  neither  neces- 
saiy  nor  reasonable. 

Hjemoolobin  and  its  Dbbitativks. 

Heemoglobin  constitutes  about  ^  of  the  corpuscles,  and, 
though  amorphous  in  the  living  blood-cells,  may  be  obtained 
in  crystals,  the  form  of  which  varies  with  the  animal;  in- 
deed, in  many  animals  this  substance  crystalliaes  spontane- 
ously on  the  death  of  the  red  cdla.  It  is  ufiique  among  albu- 
minous compounds  in  being  the  only  one  found  in  the  animal 
body  that  is  suscQptible  of  crystallization.  Its  estimated  com> 
position  is : 

Carbon 68-85 

Hydrogen r...    7*88 

Nitrogen. 16*17 

Oxygen..... ......:  81*84 

Iron '43 

Bulphur '39 

togethor  with  3  to  4  per  cent  of  water  of  crystallization. 

The  formula  assigned  is:  CwHtMOmNiMFeSt.  The  molecular 
constitution  is  not  known,  and  the  above  formula  is  merely  an 
approximation,  which  will,  however,  serve  to  convey  an  idea 


■^ 


— ".^-.ff'-f  T-     ""''."iMi 


386 


ANIMAL  PHTSIOLOOT. 


of  the  great  complexity  uf  this  compound.    The  presence  of 
iron  seems  to  be  of  great  importance.     If  not  the  essential 

respiratory  constituent,  cer- 
tainly the  administration  of 
this  metal  in  some  form 
proves  very  valuable  when 
the  blood  is  deficient  in 
heemtglobin. 

This    substance  can   be 
recogniaed  most  certainly  by 
the  spectroscope.     The  ap- 
pearances   vary   with    the 
strength   of    the    solution, 
and,  as  this  test  for  blood 
(hnmoglobin)  is   of   much 
practical  importance,  it  ¥rill 
be  necessary  to  dwell  a  little 
upon  the  subject ;  though, 
after  a  student  has  once  rec- 
ognized clearly  the  differ- 
ences of  the  spectrum  ap- 
pearances, he  has  a  sort  of 
Icnowledge  that  no  verbal 
description  can  convey.  This 
is  easily  acquired.    One  only 
needs  a  small,  flat-sided  bot- 
tle  and  a  pocket  -  spectro- 
scope.    Filling  the    bottle 
half-full  of  water,  and  getting  the  spectroscope  so  focused  that 
the  Fraunhofer  lines  appear  distinctly,  blood,  blood-stained 
serum,  a  solution  of  hamoglobin-crystals,  or  the  essential  sub- 
stance in  any  form  of  dilute  solution,  may  be  added  drop  by 
drop  till  changes  in  the  spectrum  in  the  form  of  dark  bands 
appear.    By  gradually  increasing  the  quantity,  appearances 
like  those  figured  below  may  be  observed,  though,  of  course, 
much  will  depend  on  the  thickness  of  the  layer  of  fluid  as  to 
the  quantity  to  be  added  before  a  particular  band  comes  into 

view. 

When  wishing  to  be  precise,  we  speak  of  the  most  highly 
oxidized  form  of  heemoglobin  as  oxy-hflemoglobin  (0-H),  and 
the  reduced  form  as  hamoglpbin  simply,  or  reduced  heemo- 
globin(H).  ' 

By  a  comparison  of  the  spectra  it  will  be  seen  that  the  bands 


Tut.  a6.-0nntiriltod  hMBOtfoMii  (OMtiH^ 
a.  6,  orntali  f iom  tcoow  wood  of  dim  ;  e, 
B  liiood  of  oat;  ii,o(  GnliiM-piK;  •>  o( 
;/,o« 


■MM 


presence  of 
le  eflsential 
tituent,  cer- 
listration  of 
Bome  form 
aable  when 
leficient    in 

ice  can  be 
sertainlyby 
.     The  ap- 

with  the 
e  solution, 
b  for  blood 
B  of  much 
ance,  it  will 
Iwell  a  little 
st;  though, 
las  once  rec- 

the  differ- 
lectrum  ap- 
as  a  sort  of 
,  no  verbal 
onvey.  This 
L  One  only 
ftt-sided  bot- 
cet  -  spectro- 

the  bottle 
focused  that 
>lood-8tained 
flsential  sub- 
ied  drop  by 
I  dark  bands 
appearances 
h.  of  course, 
[)f  fluid  as  to 
i  comes  into 

most  highly 
a  (0-H),and 
luced  heemo- 

lat  the  bands 


THB  BESPIRATOBT  SYSTEM. 


887 


of  oxy-hffimoglobin  lie  between  the  D  and  j;  lines;  that  the 
left  band  near  D  is  always  the  moat  definite  in  outline  and  the 


most  pronounced  in  every  respect  except  breadth ;  that  it  is  in 
weak  solutions  the  first  to  appear,  and  the  last  to  disappear  on 


f.atiV.>\^Vn 


888 


ANIMAL  PHTSIOLOOY. 


reduction ;  that  there  are  two  instances  in  which  there  may  be 
a  single  band  from  heemoglobin — ^in  the  one  case  when  the  solu- 
tion is  very  dilute  and  when  it  is  very  concentrated.  These 
need  never  be  mistaken  for  each  other  nor  for  the  band  of  re- 
duced heemoglobin.  The  latter  is  a  hasy  broad  band  with  com- 
paratively indistinct  outlines,  and  darkest  in  the  middle. 

It  will  be  further  noticed  that  in  all  these  instances,  apart 
from  the  bands,  the  spectrum  is  otherwise  modified  at  each 
end,  so  that  the  darker  the  more  centrally  placed  characteristic 
bands,  the  more  is  the  light  at  the  same  time  out  off  at  each 
end  of  the  spectrum. 

If,  now,  to  a  specimen  showing  the  two  bands  of  oxy-heemo- 
globin  distinctly  a  few  drops  of  ammonium  sulphide  or  other 
reducing  agent  be  added,  a  change  in  the  color  of  the  solution 
will  result,  and  the  single  hasy  band  characteristic  of  heemo- 
globin will  appear. 

It  is  not  to  be  supposed,  however,  that  venous  blood  gives 
this  Bpe«jtrum.  Even  after  asphyxia  it  will  be  difficult  to  see 
this  band,  for  usually  some  of  the  oxy-heemoglobin  remains 
reduced ;  but  it  is  worthy  of  note,  as  showing  that  the  appear- 
ances are  normal,  that  the  blood,  viewed  through  thin  tissues 
when  actually  circtdating,  whether  arterial  or  venous,  gives 
the  spectrum  of  oxy-heBmoglobin.  At  the  same  time  there  can 
be  no  doubt  that  the  changes  in  color  which  the  blood  under- 
goes in  passing  through  the  capillaries  is  due  chiefly  to  loss  of 
oxygen,  as  evidenced  by  the  experiments  before  referred  to ;  and 
the  reason  that  the  two  bands  are  always  to  be  seen  in  venous 
blood  is  simply  that  enough  oxy-heemoglobin  remains  to  give 
the  two-band  spectrum  which  prevails  over  that  of  (reduced) 
heemoglobin.  We  are  thus  led  by  many  paths  to  the  important 
conclusion  that  the  red  corpuscles  are  oxygen-carriers,  and, 
though  this  may  not  be  and  probably  is  not  their  only  func- 
tion, it  is  without  doubt  their  principal  one.  Of  their  oxygen 
they  are  being  constantly  relieved  by  the  tissues;  hence  the 
necessity  of  a  circulation  of  the  blood  from  a  req)iratory  point 
of  vidw. 

There  are  other  gases  that  can  replace  oxygen  and  form 
compounds  with  heemoglobin ;  L<)nce  we  have  GO-heemoglobin 
and  NO-heemoglobin,  which  in  turn  are  replaced  by  oxygen  with 
no  little  difficulty— a  fact  which  explains  why  carbonic  oxide  is 
so  fatal  when  respired,  and,  as  it  is  a  constituent  of  illuminat- 
ing gas,  the  cause  of  the  death  of  those  inhaling  the  latter  is 
often  not  far  to  seek.    Blood  may,  in  fact,  be  saturated  with 


iilfiiiliriiiTi 


THE  RESPIRATORY  SYSTEM. 


889 


ere  may  be 
m  the  solu- 
»d.  These 
band  of  re- 
l  with  com- 
idle. 

mces,  apart 
led  at  each 
aracteristic 
off  at  each 

oxy-hflBmo- 
de  or  other 
the  solution 
Ic  of  heemo- 

blood  gives 
fficult  to  see 
bin  remains 
the  appear- 
thin  tissues 
enous,  gives 
me  there  can 
blood  under- 
»fly  to  loss  of 
jrredto;  and 
en  in  venous 
lains  to  give 
of  (reduced) 
he  important 
»rrier8,  and, 
ir  only  func- 
their  oxygen 
«;  hence  tiie 
(iratory  point 

;en  and  form 
^-heemoglobin 
f  oxygen  with 
bonic  oxide  is 
of  illuminat- 
g  the  latter  is 
kturated  with 


carbonic  oxide  by  allowing  illuminating  gas  to  pass  through  it, 
when  a  change  of  color  to  a  cherry  red  may  be  observed,  and 
which  will  remain  in  spite  of  prolonged  shaking  up  with  air  or 
attempts  at  reduction  with  the  usual  reagenta  Heemoglobin 
may  be  resolved  into  a  proteid  (globin)  not  well  understood, 
and  hanudin.  This  happens  when  the  blood  is  boiled  (perhaps 
also  in  certain  cases  of  lightning-stroke),  and  when  strong  acids 
are  added.  Hsematin  is  soluble  in  dilute  acids  and  alkalies,  and 
has  then  characteristic  spectra.  Alkaline  hematin  may  be  re- 
duced ;  and,  as  the  iron  can  be  separated,  resulting  in  a  change 
of  color  to  brownish  red,  after  which  there  are  no  longer  any 
reducing  effects,  it  would  seem  that  the  oxygen-carrying  power 
and  iron  are  associated.  This '  iron-free  htematin  is  named 
hamaioporphyrin  or  Ttamatoin. 

Hamin  is  hydrochlorate  of  hematin  (Teichmann's  crystals), 

and  may  be  formed  by  adding  glacial  acetic  acid  and  common 

salt  to  blood,  dried  blood-clot,  etc.,  and  heating  to  boiling.  This 

'is  one  of  the  best  tests  for  blood,  valuable  in  medico-legal  and 

other  cases. 

When  oxy-hsemoglobin  stands  exposed  to  the  air,  or  when 
diffused  in  urine,  it  changes' color  and  becomes^  in  fact,  another 
i^ubstance — metJuemoglobin,  irreducible  by  other  gases  (CO,  etc.), 
and  not  surrendering  its  oxygen  in  vacuo,  though  giving  it  up 
to  ammonium  sulphide,  becoming  again  oxy-heemoglobin,  when 
shaken  up  with  atmospheric  air.  Its  spectrum  differs  from 
that  of  oxy-heemoglobin  in  that  it  has  a  band  in  the  red  end  of 
the  spectrum  between  the  C  and  D  lines.  HameUoidin  is  some- 
times found  in  the  body  as  a  remnant  of  old  blood-clots.  It  is 
probably  closely  allied  to  if  not  identical  with  the  bUirubin 
of  bile. 

Ooiq^anittft.— While  hemoglobin  is  the  respiratory  agent  in 
all  the  groups  of.  vertebrates,  this  is  not  true  of  the  inverte- 
brates. Red  blood-cells  have  as  yet  been  found  in  but  a  few 
species,  though  heemoglobin  does  exist  in  the  blood  plasma  of 
several  groups,  to  one  of  which  the  earth-worm  and  several 
other  annelids  belong.  It  is  interesting  to  note  that  the  respir- 
atory compound  in  certain  families  of  crustaceans,  as  the  com- 
mon crab,  horseshoe-crab  (limulus),  etc.,  is  blue,  and  that  in 
this  substance  copper  seems  to  take  the  place  of  iron. 

Tht  Vitngw  miA  tin  Ouboi  DlMdd*  «f  tlw  Hood.— The  little 
nitrogen  which  is  found  in  about  equal  quantity  in  venous  and 
arterial  blood,  seems  to  be  simply  dissolved.  The  relations  of 
carbonic  anhydride  are  much  more  complex  and  obscure.    The 


890 


ANIMAL  PHTSIOLOGT. 


main  facts  known  are  that — 1.  The  quantity  of  this  gas  is  as 
great  in  serum  as  in  blood,  or,  at  all  events,  the  quantity  iu 
serum  is  very  large.  2.  The  greater  part  may  be  extracted  by 
an  exhaustion-pump ;  but  a  small  percentage  (3  to  6  volumes 
per  cent)  does  not  yield  to  this  method,  but  is  given  off  when 
an  acid  is  added  to  the  serum.  3.  If  the  entire  blood  be  sub- 
jected to  a  vacuum,  tLe  whole  of  the  COt  is  given  off. 

From  these  facts  it  has  been  conclude:^  that  the  greater  part 
of  the  COt  exists  in  the  plasma,  associated  probably  with  sodium 
salts,  as  isodium  bicarbonate,  but  that  the  corpuscles  in  some 
way  determine  its  relations  of  association  and  disassociation. 
Some  think  a  good  deal  of  this  gas  is  actually  united  with  the 
red  corpuscles. 

We  may  now  inquire  into  the  more  intimate  nature  of  respi- 
ration in  the  blood.  From  the  facts  we  have  stated  it  is  obvi- 
ous that  respiration  can  not  be  wholly  explained  by  the  Henry- 
Dalton  law  of  pressures  or  any  other  physical  law.  It  is  also 
plain  that  any  explanation  which  leaves  out  the  principle  of 
pressure  must  be  incomplete. 

While  there  is  in  oxy-heemoglobin  a  certain  quantity  of  oxy- 
gen, which  is  intra-molecular  and  incapable  of  removal  by  re- 
duction of  pressure,  there  is  also  a  portion  which  is  subject  to 
this  law,  though  in  a  peculiar  way;  nor  is  the  question  of 
temperature  to  be  excluded,  for  experiment  shows  that  less 
oxygen  is  taken  up  by  blood  at  a  high  than  at  a  low  tempera- 
ture. 

We  have  learned  that,  in  ordinary  respiration,  the  propor- 
tion of  carbonic  dioxide  and  oxygen  in  (Ufferent  parts  of  the 
respiratory  tract  must  vary  greatly ;  the  air  of  necessity  being 
much  less  pure  in  the  alveoli  than  in  the  larger  bronchi. 

From  experiments  on  blood,  venous  and  arterial,  to  deter- 
mine the  conditions  of  pressure,  temperature,  etc,  under  which 
the  injurious  gas  is  got  rid  of  and  the  necessary  one  absorbed, 
it  has  been  found  that  the  partial  pressure  of  oxygen  in  the 
lungs  is  sufficient  to  bring  about  that  surrender  of  oxygen  to 
the  blood  necessary  to  keep  it  all  but  saturated  with  this  gas 
as  it  is  believed  to  be ;  and  that,  so  far  as  carbonic  anhydride 
is  concerned,  the  same  law  holds—i  a,  the  partial  pressure  in 
the  blood  is  ordinarily  greater  than  in  the  alveoli. 

By  means  of  an  apparatus  by  which  one  of  the  smaller 
bronchi  may  be  occluded  for  a  certain  period,  and  also  allow 
of  withdrawal  of  samples  of  the  air  in  the  occluded  portion  of 
lung  from  time  to  time,  to  ascertain  its  composition,  attempts 


THE  BBSPIBATORT  8T8TE1L 


891 


is  gas  M  as 
[quantity  iu 
ctracted  by 
I  6  volumes 
in  off  when  . 
Qod  be  sub- 
ff. 

greater  part 
iritb  sodium 
les  in  some 
lassociation. 
»d  with  the 

are  of  respi- 
d  it  is  obvi- 
'  the  Henry- 
r.  It  is  also 
principle  of 

itity  of  oxy- 
noval  by  re- 
LS  subject  to 
question  of 
nrs  that  less 
owtempera- 

the  propor- 
parts  of  the 
lessity  being 
>nchi. 

ial,  to  deter- 
under  which 
ne  absorbed, 
ygen  in  the 
>f  oxygen  to 
rith  this  gas 
io  anhydride 
pressure  in 

the  smaller 
d  also  allow 
Bd  portion  of 
on,  attempts 


have  been  made  to  determine  the  pressure  relations  within  an 
alveolus.  It  is  maintained  that  while  the  partial  pressure  of 
the  carbonic  anhydride  rises  and  of  the  oxygen  sinks,  still  that 
they  remain  such  as  to  favor  respiration.  It  is  also  found  that, 
in  the  asphyxia  following  occlusion  of  the  trachea,  the  tension 
of  oxygen  is  always  greater,  and  of  carbonic  anhydride  less,  ia 
the  alveoli  than  in  the  blood.  On  the  other  hand  it  is  stated 
that  oxy-IuBmoglobin  is  found  in  the  blood  whoa  every  trace  of 
oxygen  is  removed  from  a  chamber  in  which  an  asphyxiating 
animal  is  breathing,  so  that  it  is  argued  that  partial  pressures 
alone  can  not  explain  the  facts  of  respiration,  and  that  this 
function  is  fundamentally  a  chemical  process;  and  it  is  cus- 
tomary to  speak  of  the  oxygen  of  oxy-hemoglobin  as  being  in 
a  state  of  "  loose  chemical  combination." 

The  entire  truth  seems  to  lie  in  neither  view,  though  both 
are  partially  correct 

The  view  expressed  by  some  phjrsiologists,  to  the  effect  that 
diffusion  explains  the  whole  matter,  so  far,  at  least,  as  carbonic 
anhydride  is  concerned,  and  that  the  epithelial  eejls  of  the  lung 
have  no  share  in  the  rospiratory  process,  does  not  seem  to  be 
in  harmony  either  with  ttie  facts  of  respiration  or  with  the 
laws  of  biology  in  general.  Why  not  say  at  once  that  the  facts 
of  respiration  show  that,  here  as  in  other  parts  of  the  economy, 
while  physical  and  chemical  laws,  aa  we  hnoto  tJiem,  stand 
related  to  the  vital  processes,  yet,  by  reason  of  being  vital 
processes,  we  can  not  explain  tiiem  according  to  the  theories  of 
either  ph3ir8iai  or  chemistry  ?  Surely  this  very  subject  show^ 
that  neither  chemistry  nor  physics  is  at  present  adequate  to/ 
explain  such  processes.  It  is,  of  course,  of  value  to  know  the 
circumstances  of  tension,  temperature,  etc.,  under  which  respi- 
ration takes  place.  We,  however,  maintain  that  these  are  con- 
ditions only—essential  no  doubt,  "but,  though  important,  that 
they  do  not  make  up  the  process  of  respiration.  But,  because 
we  do  not  know  the  real  explanation,  let  us  not  exalt  a  few 
facts  or  theories  of  chemistry  or  phyidos  into  a  solution  of  a 
complex  problem.  Besides,  some  of  tiie  experiments  on  which 
the  oondiosions  have  been  based  are  questionable,  inasmuch  as 
they  seem  to  inducN»  artificial  conditions  in  the  animals  oper- 
ated upon ;  and  we  have  already  insisted  on  the  blood  being 
regarded  as  a  living  tissue,  behaving  differently  in  the  body 
and  when  isolated  from  it,  so  that  even  in  so-ci^ed  blood-gas 
experiments  there  may-  be  sources  of  fallacy  inherent  in  the 
nature  of  the  case. 


892 


ANIMAL  PHYSIOLOGY. 


Vordgn  0mm  and  SMpintion. — ^These  are  divided  into : 

1.  Indifferent  gases,  as  N,  H,  CH*,  which,  though  not  in 
themselves  injurious,  are  entirely  useleM  to  the  economy. 

3.  Pbisonotia  gases,  fatal,  no  matter  how  abundant  the  nor* 
mal  respiratory  food  may  be.  They  are  divisible  into:  (a)  those 
that  kill  by  displaqing  oxy^n,  as  NO,  GO,  HON ;  (&)  narcolie 
gases,  as  CO*,  NtO,  producing  asphyxia  when  present  in  large 
quantities;  (c)  reducing  gases,  as  HiS,(NH«)iS,  PH(,As^C»N(, 
which  rob  the  heemoglobin  of  its  oxygen. 

There  are  probably  a  number  of  poisonous  products,  some 
of  them  possibly  gasee^  produced  by  the  tissues  themselves  and 
eliminated  normally  by  the  respiratory  tract;  and  these  are 
doubtless  greatly  augmented,  either  in  number  or  quantity,  or 
both,  when  other  excreting  organs  are  disordered. 


Respiration  in  the  Tissues. 

We  first  direct  attention  to  certain  striking  facts : 
1.  An  isolated  (frog's)  muscle  will  continue  to  contract  for 
a  considerable  period  and  to  exhale  carbon  dioxide  in  the  total 
absence  of  oxygen,  as  in  an  atmosphere  of  hydrogen;  though, 
of  course,'there  is  a  limit  to  this,  and  a  muscle  to  which  either 
no  blood  .flows,  or  only  venous  blood,  soon  shows  signs  of 
fatigue.  2.  In  a  frog,  in  which  physiological  saline  solution 
has  been  substituted  for  blood,  the  metabolism  will  continue, 
carbonic  anhydride  being  exhaled  as  usual.  8.  SubetancM, 
which  are  readily  oxidized*  when  introduced  into  the  blood  of 
a  living  animal  or  into  that  blood  when  withdrawn  undergo 
but  little  oxidative  change.  4,  An  raitire  frog  will  respire  oar> 
bonic  dioxide  for  hours  in  an  atmosphere  of  nitrogen. 

Such  facts  as  these  seem  to  teach  certain  lessons  dearly.  It 
is  evident,  first  ^f  all,  that  the  oxidative  prooessM  that  give  rise 
to  carbon  dioxide  occur  chiefly  in  the  Hssues  and  not  in  the 
blood ;  that  in  the  case  of  muscle  the  oxygen  that  is  Used  is  first 
laid  by,  banked  as  it  were  against  a  time  of  need,  in  tiici  form  of 
intra-moleoular  oxygen,  which  is  again  set  free  in  the  form  of 
carbon  dioxide,  but  by  what  seriM  of  changM  we  are  quite  un- 
able tu  say.  "IRiough  our  knowledge  of  the  rMpiratory  prooessM 
of  muscle  is  greater  than  for  any  other  tissue,  there  seems  to 
be  no  reason  to  believe  that  th6y  are  essentially  diflFerent  else- 
where. The  ad  vantagM  of  this  .banking  of  oxygen  are,  of  course, 
obvious ;  were  it  otherwise,  the  life  of  every  cell  mui^  be  at  the 
mercy  of  the  ^lightest  interruption  of  the  flow  of  blood,  the 


THB  RBSPIRATORT  ST8TE1L 


898 


nto: 

Lgh  not  in 

omy. 

it  the  nor- 

):  (a)  those 

[b)  narcotie 

tit  in  large 

AbH.,C.Ni^ 

iucts,  some 
aselves  and 
1  these  are 
[uantity,  or 


i: 

iontract  for 
in  the  total 
»n;  though, 
rhich  either 
rs  signs  of 
ine  solution 
11  continue. 
Substances, 
the  blood  of 
wn  undergo 
respire  oar^ 
m. 

I  clearly.  It 
hat  give  rise 
I  not  in  the 
I  tised  is  first 
.  thet  form  of 
L  the  form  of 
ure  quite  un- 
jry  processes 
ere  seems  to 
lifferent  else- 
,re,  of  course, 
ust  be  at  the 
>f  blood,  the 


/  1«WB 


entrance  of  air,  etc.  Even  as  it  is,  the  need  of  a  oonatant  supply 
of  oxygen  in  warm-blooded  animals  is  much  greater  than  in 
cold-blooded  creatures,  which  can  long  endure  almost  entire 
cessation  of  both  respiration  and  circulation,  owing  to  the  com- 
paratively slow  rate  of  speed  of  the  vital  machinery. 

If  one  were  to  rely  on  mere  appearances  he  might  suppose 
that  in  the  more  active  condition  of  certain  organs  there  was 
less  chemical  interchange  (respiration)  between  the  blood  and 
the  tissues  than  in  the  resting  stage,  or,  properly  speaking, 
more  tranquil  stage,  for  it  must  be  borne  in  mind  tiiat  a  living 
cell  is  never  wholly  at  rest;  its  molecular  changeejwe  cease- 
less. It  happens,  e,  g.,  that  wE^ToBriwi  giJii^ads  (saiivMyTi'e 
Siecreting  actively,  the  blood  flowing  from  them  is  less  venous 
in  appearance  than  when  not  functionally  active.  This  is  not 
because  less  oxygen  is  used  or  lees  abstracted  from  the  blood, 
but  because  of  the  greatly  increased  qieed  of  the  blood-flow,  so 
that  the  total  supply  to  draw  from  is  so  much  larger  that, 
though  more  oxygen  is  actually  used,  it  is  not  so  much  missed, 
nor  do  the  greater  additions  of  carbon  dioxide  so  rapidly  pol- 
lute this  rapid  stream. 

It  is  thus  seen  that  throughout  the  animal  kingdom  respira- 
tion is  fnndMnentally  the  same  process.  It  is  in  every  case 
finally  a  consumption  of  oxygen  and  production  of  carbonic 
anhydride  by  the  individual  cell,  whether  that  be  an  Amceba 
or  an  element  of  man's  brain.  These  are,  however,  but  the\ 
beginning  and  end  of  a  very  complicated  biological  history  of  ( 
by  far  the  greater  part  of  which  nothing  is  yet  known ;  and  itN 
must  be  admitted  that  diffusion  or  any  physical  explanationj 
carries  us  but  a  litUe  way  on  toward  the  understanding  of  it.  "^ 

The  Nbsvous  Stbtuc  in  Relation  to  Rmhpibation. 

We  have  considered  the  muscular  movements  by  which  the 
air  is  made  to  enter  and  leave  the  lungs  in  consequence  of 
changes  in  the  diameters  of  the  air-inclosing  case,  the  thorax. 
It  remains  to  examine  into  the  means  by  which  these  muscles 
were  set  into  harmonious  action  so  as  to  accomplish  the  pnr^ 
pose.  The  nerves  supplying  the  musdee  of  req>iration  are  de- 
rived from  the  spinal  cord,  so  that  they  must  be  under  the 
dominion  of  central  nerve-oells  situated  either  in  the  cord  or 
the  brain.  Is  the  influence  that  proceeds  outward  generated 
within  the  cells  independently  of  any  afferent  impulses,  or  is  it 
dependent  on  such  causes  f   Let  us  appeal  to  facts. 


894 


ANIMAL  PHTSIOLOGT. 


1.  If  the  phrenics,  an  intercostal  nerve,  etc.,  be  cut,  there  is 
a  corresponding  pan^ysis  of  the  mnscle  supplied.  2.  If  the 
spinal  cord  be  divided  below  the  mednlla  oblongata,  there  is  a 
cessation  of  all  respiratory  movements  except  those  of  the 
larynx  and  face,  which  also  disappear  if  the  facial  and  inecur- 
rent  laryngeal  nerves  be  divided.  3.  So  long  as  the  medulla 
remains,  respiration  may  continue;  but  if  even  a  small  part  of 
this  region,  situated  below  the  vaso-motor  center  between  this 
and  the  ccdamus  acriptorius  (respiratory  center,  ruBud  vital), 
be  injured,  death  ensues  rapidly.  Plainly,  then,  there  are  cen- 
tral cells  which  originate  the  impulses  that  energize  the  mus- 
cles. 

It  remains  to  inquire  still  whether  they  an:  independent 
(automatic)  centers,  or  are  influenced  by  impulsv>8  reaching 
them  from  without.  Is  the  government  absolute,  or  subject  to 
the  will  of  the  multitudinous  cells  of  the  organic  common- 
wealth ? 

Again  let  us  appeal  to  facts:  1.  If  one  vagus  nerve  be  cut, 
a  change  is  observable  in  the  respiratory  rhjrthm,  which  is 
much  more  pronounced  if  both  nerves  be  divided.  Respiration 
becomes  slower,  and  the  pause  between  inspiration  and  expira- 
tion greatly  leiigthened,  though  th^  gaseous  interchange  re- 
mains much  as  before.  S.  If  one  suddenly  step  into  a  cold 
bath,  he  naturally  draws  a  long  breath.  Again,  the  respiration 
is  very  greatly  idtered  in  conaequenoe  of  emotional  clumges; 
indeed,  there  iis  probably  no  rhythm  in  the  body  more  subject 
to  frequent  obvious  altwation  than  that  of  respiration.  8. 
Stimulation  of  the  central  end  of  such  a  nerve  as  the  sciatic 
causes  marked  change  in  the  rhythm  of  breathing.  4.  Stimu- 
lation of  the  central  end  of  the  vagus  usually  quickens  res- 
piration, whil^  stimulation  of  the  central  end  of  the  superior 
laryngeal  has  the  opposite  effect.  If  the  current  be  strong, 
respiration  may  bo  arrested  in  each  instance,  though  in  a  differ- 
ent manner.  In  the  case  of  vagus  stimulation  the  result  id 
inspiratory  spasm,  and  of  the  superiw  laryngeal  eitpiratory 
spasm. 

These  and  a  host  of  additional  facts,  experimental  and  other, 
show  that  the  central  impulses  are  modified  by  afferent  im- 
pulses reaching  the  center  through  appropriate  nerves.  More- 
over, drugs  seem  to  act  directly  on  tiie  center  through  the 
blood. 

The  vagus  is  without  doubt  the  afferent  respiratory  nerve, 
though  how  it  is  affected,  whether  by  the  mechanical  movement 


THE  BBSPIRATORT  STBTBM. 


896 


;nt,  tiliere  is 
.  2.  If  the 
I,  there  is  a 
bose  of  the 
I  and  recur- 
the  medulla 
imall  part  of 
Mtween  this 
noRvd  vital),  , 
lere  are  cen- 
ize  the  mtis- 

independent 
.808  reaching 
or  subject  to 
nic  common- 

lerve  be  cut, 
im,  which  is 
Bespiration 
1  and  ezpira- 
terohange  re- 
p  into  a  cold 
be  respiration 
»nal  clumges; 
more  subject 
ispiration.    8. 
as  the  sciatic 
ig.    4.  Stimu- 
quickens  res- 
f  the  superior 
tnt  be  strong, 
ighinadiffer- 
L  the  result  id 
aal  expiratory 

ntal  and  other, 
f  afferent  im- 
lerves.  More- 
r  through  the 

►iratory  nerve, 
ioal  movement 


of  the  lungs  merely,  by  the  condition  of  the  blood  as  regards  its 
contained  gases,  or,  as  seems  most  likely,  by  a  combination  of 
circumstances  into  which  these  enter  and  are  probably  the 


Bntn  oteoe  meduffc  A»m  whtek 
-imnOm  ModMrliig  rmplnUim 
man  proceed. 


Jfi^pli'iiCof  y 
inaumeduna. 


Vm.  m.-I>iacnm  latoBdMl  la 


BJptMt  tortf.— > 


OrtatMOMimrw 
/  fum/n 
taqwtawi 
ptrotery  eetdn  tv'* 


ooorw  of  ImpolMa. 


o(f«|ilratloa.   Arrawa 


principal,  is  not  demonstrably  clear.    When  othons  function  as 
afferent  nerves^  capable  of  modifying  the  action  of  the  respira- 


ffiiMiwiliiwiiiiiiitw 


396 


ANIMAL  PHYSIOLOGT. 


¥ 


tory  center,  they  are  probably  influenced  by  the  respiratory 
condition  of  the  blood,  though  not  necessarily  exclusively. 

But  when  all  the  principal  a£Ferent  impulses  are  cut  off  by 
division  of  the  nerves  reaching  the  respiratory  center  directly 
or  indirectly,  respiration  will  still  continue,  provided  the  motor 
nerves  and  the  medulla  remain  intact. 

The  center,  then,  is  not,  mainly  at  least,  a  reflex  but  an  auto- 
matic one,  though  its  action  is  modified  by  afferent  impulses 
reaching  it  from  eVery  quarter.  Since  respiration  continues 
when  the  medulla  is  divided  in  the  middle  line,  yet  is  modified 
unilaterally  when  one  vagus  is  divided,  it  is  inferred  that  the 
respiratory  center  is  double,  that  each  half  usually  works  in 
harmony  with  the  other,  but  that  each  can  act  independently. 
Though  it  seems  clear  enough  that  the  respiratory  center  is 
automatic,  and  that  its  action  is  modified  according  to  the  con- 
dition of  the  organism  generally,  as  communicated  to  it  by  the 
various  afferent  nerves  and  the  blood  itself,  yet  the  exact  man- 
ner of  its  action — ^why  inspiration  follows  up  expiration— has 
not  been  clearly  explsdned.  Some  assume  that  during  expira- 
tion inspiratory  impulses  are  gathering  head  and  finally  check 
expiration  by  originating  inspiration,  while  these  are  opposed 
by  another  process  which  at  length  gives  rise  to  enough  resist- 
ance to  check  inspiration,  and  originate  expiration ;  and  this 
theory  becomes  more  complete  if  an  expiratory  as  well  as  in- 
spiratory center  be  assumed. 

We  have  hitherto  spoken  only  of  a  single  respiratory  cen- 
ter in  the  medulla,  but  certain  experimental  facts  throw  addi- 
tional light  on  the  subject. 

In  young  mamnuils— e.  g.,  kittens— it  is  found  that,  in  the 
absence  of  the  medulla*  respiratory  movements  may  be  induced 
by  stimulating  (pinching)  the  turiace,  especially  if  the  action 
of  the  spinal  cord  be  Augmented  by  the  administration  of 
strychnia.  From  this  it  hew  been  inferred  that  there  are  respir- ' 
atory  centers  in  the  spinal  cord,  subordinate  to  the  main  cen- 
ter in  the  medulla.  Oonndering  the  imperfect  nature  of  the 
respiratory  act  as  thus  induced,  and  the  circumstances  of  the 
case,  the  conclusion  has  the  appearance  of  being  a  little  strained. 
But  quite  recently  it  has  been  shown  that  ba.  the  adult  dog 
when  the  cord  is  severed  below  the  medulla*  and  artificial  res- 
piration maintained  for  some  time,  on  ceasing  this,  breathing 
begins  spontaneously  and  continues  for  a  considerable  period ; 
and  the  expiratory  phase  of  req>iration  in  this  case  is  the  most 
marked.    It  has  been  argued  from  this  experiin^:,%ai^  tliere 


respiratoi^y 
sively. 
J  cut  oflE  by 
ter  directly 
1  the  motor 

rat  on  auto- 
oit  impalses 
n  continues 
\  is  modified 
>ed  that  the 
ly  works  in 
lependently. 
ry  center  is 
j;  to  the  con- 
to  it  by  the 
)  exact  man- 
iration— has 
iringexpira- 
&nally  check 
are  opposed 
lOugh  resist' 
on;  and  this 
swell  as  in- 

piratory  cen- 
I  throw  addi- 

1  that,  in  the 
ty  be  induced 
if  the  action 
nistration  of 
erearerespir-' 
lie  main  cen- 
lature  of  the 
itances  of  the 
little  strained, 
the  adult  dog 
[  artificial  res- 
his,  breathing 
srable  period; 
kse  is  the  most 
ant  t^t  there 


THB  RESPIBATORT  STSTEBL 


897 


arc  both  inspiratory  and  expiratory  centers  in  the  spinal  cord. 
But,  as  we  have  pointed  out,  on  more  than  one  occasion,  we 
must  always  be  on  our  guard  in  interpreting  the  behavior  of 
one  i>art  when  another  is  out  of  gear.  There  is  so  much  latent 
resource,  so  great  a  power  to  resume  functions  normally  laid 
aside,  if  not  wholly  in  great  part,  that  we  should  hesitate  be- 
fore inferring  that  the  spinal  cord  usually  takes  a  prominent 
share  in  originating  the  impulses  which  govern  respiration. 
Notwithstanding  the  suggestiveness  of  such  exi)eriments,  we 
do  not  think  they  make  the  medulla  appear  in  a  less  important 
light  as  the  part  of  the  nervous  system  dominant  in  respira- 
tion ;  though  there  may  be  nervous  machinery  in  the  cord  usu- 
ally in  feeble  action,  susceptible  of  assuming  a  more  exalted 
functional  HUe  when  occasion  urgently  demands  and  when  en- 
couraged, so  to  speak,  to  do  so,  as  in  the  experiments  referred 
to  above;  indeed  such,  upon  our  own  theory  of  physiological 
reversion,  would  natturally  be  the  case.  We  must,  however, 
draw  the  line  between  what  is  and  what  may  be  is  function. 

The  Tnfliwioe  ef  fhe  Ooodttlm  «f  the  Btooi  ia  XeipintioB^— If 
for  any  reason  the  tissues  are  not  receiving  a  due  supply  of 
oxygen,  they  manifest  their  disapproval,  to  speak  figuratively, 
by  reports  to  the  responsible  center  in  the  medulla,  and  if  the 
medulla  is  a  sharer  in  the  lack,  as  it  naturally  would  be,  it  takes 
action  independently.  One  of  the  most  obvious  instances  in 
which  there  is  okygen  starvation  is  when  there  is  hindrance  to 
the  entrance  of  air,  owing  to  obstruction  in  the  respiratory 
tract. 

At  first  the  breathing  is  merely  accelerated,  with  perhaps 
some  increase  in  the  depth  of  the  inspirations  {hyperpn<Ka),  a 
stage  which  is  soon  succeeded  by  labored  breathing  (dyspncMi), 
which,  after  the  medulla  has  called  all  the  muscles  usually  em- 
ployed in  respiration  into  violent  action,  psuues  into  convul- 
sions, in  which  every  muscle  may  take  part 

In  other  words,  the  respiratory  impulses  not  only  pass  along 
their  usual  pi^hs  as  energetically  as  possible,  but  radiate  into 
unusual  ones  and  pass  by  nerves  not  commonly  thus  set  into 
functional  activity. 

It  would  be  more  correct,  perhaps  to  assume  that  the  vari- 
ous parts  of  the  nervous  system  are  so  linked  together  that  ex- 
cessive activity  of  one  set  of  connections  acts  like  a  stimulus  to 
rouse  another  set  into  action,  the  order  in  which  this  happens 
depending  on  the  law  of  habit^habit  personal  and  especially 
ancestral.    An  opposite  condition  to  that  described,  known  as 


itwywmwJBHWKiwmiaMi 


MiilMiaWIIBIlBIIIWnBMI 


898 


ANIMAL  PHT8I0L00T. 


apnaa,  may  be  indnced  by  pomping  air  into  an  animal's  chest 
very  rapidly  by  a  bellows;,  or  in  one's  self  by  a  suooeesion  of 
rapid,  deep  respirations. 

After  ceasing,  the  breathing  may  be  entirely  interrupted 
for  a  Inrief  interval,  then  conunenee  very  quietly,  gradually  in> 
creaoing  to  the  normaL 

Apncea  has  been  interpreted  in  two  ways.  Some  think  that 
it  is  due  to  fatigue  of  the  muscles  of  respiration  or  the  respira> 
tory  center;  others  that  the  blood  has  under  these  circum- 
stances an  excess  of  oxygen,  whidi  so  influences  the  respiratory 
center  that  it  is  quieted  (inhibited)  for  a  time. 

The  latter  yiew  is  that  usually  sidopted ;  but,  considering  that 
apfMsa  results  from  the  sobbing  of  children  following  a  pro- 
longed fit  of  crying,  also  in  Cheyne-Stokes  and  other  abnonnal 
forms  of  breathing,  and  thai  the  blood  is  normally  almost  satu- 
rated with  oxygen,  it  will  be  agreed  that  there  is  a  good  deal 
to  be  said  for  the  first  view,  especially  thai  part  of  it  which 
represents  the  cessation  uf  breathing  as  owing  to  excessive 
activity  and  exhaustion  of  the  respiratory  centw.  We  find 
such  a  calm  in  asphyxia  after  the  convulsive  storm. 

Is  it,  then,  the  excessive  accumulation  of  carbon  dioxide  or 
the  deficiency  of  oxygen  that  induces  dyspnoea  f  Considering 
that  the  former  gas  acts  as  a  narcotic,  and  does  not  induce  con- 
vulsions, even  when  it, constitutes  a  large  percentage  of  the 
atmosphere  breathed,  and  that  the  need  of  oxygen  for  the  tis- 
sues is  constant,  it  certainly  seem^  most  reasonable  to  conclude 
that  the  phenomena  of  dyspnoea  are  owing  to  the  lack  of  oxy- 
gen chiefly,  at  least ;  thxHigh  the  presence  of  an  excess  of  car- 
bonic anhydride  may  take  some  share  in  arousing  that  vigorous 
effort  on  the  part  of  the  n«irvous  system,  to  restore  the  func- 
tional equilibrium,  so  evident  under  the  circumstances. 

Ths  dh^MMtos  BsspifatioB  (gtowsnaaX— There  is  a  form 
of  breathing  occurring  under  a  variety  of  abnormal  circum- 
stances, xa  which  the  respirations  gradually  reach  a  maximum 
(dyspnoaa),  and  then  as  gradually  decline  to  absolute  cessation 
(apnoea).  The  pause  may  last  a  su^rising  length  of  time  (one 
half  to  three  quarters  of  a  minute),  when  this  form  of  breathing 
again  repeats  itself.  It  has  been  compared  to  the  periodic 
grouping  of  heart-beats  (Luciani  groups),  occurring  when  the 
organ  is  suffering.  There  is  abundant  cause  usually  for  ex- 
haustion of  the  center,  on  account  of  disordered  blood  or  an 
insufficient  supply  to  the  Inain.  This  phenomenon  and  apnoea 
bring  out  clearly  the  rhythmic  character  of  those  processes. 


mmmtm 


>W)M.M.iW  ^iiw  II 


THE  RBSnBATORT  8T8TEM. 


899 


mars  cheat 
looession  of 

interrupted 
radoally  in- 

» think  that 
therespira- 
ese  ciromn- 
respiratory 

ideringthat 
wing  apro- 
HrabnOTmal 
alinoet  satu- 

a  good  deal 
of  it  which 
to  excessive 
r.  We  find 
I. 

tn  dioxide  or 
Ck>nsidering 
;  induce  con- 
itage  of  the 
a  for  the  tis- 
)  to  conclude 
lack  of  oxy- 
xcessof  car- 
ihat  vigorous 
>Te  the  funo- 
nces. 

lere  is  a  form 
rmal  circum- 
i  a  maximum 
lute  cessation 

of  time  (one 
L  of  breathing 

the  periodic 
ing  when  the 
tually  for  ex- 
.  blood  or  an 
}n  and  apnoea 
Dse  processes. 


like  respiration,  which  in  the  nature  of  the  case  must  be  in 
the  higher  groups  of  vertebrates  ceaseless,  and  it  is  not  surpris- 
ing that,  like  a  lame  dog,  which  prefers  progression  by  three 
legs  to  none  at  all,  the  ever-active  center  will  keep  up  its  rhythm 
as  long  as  it  can— perfectly,  if  possible,  and,  if  not  perfectly,  as 
well  as  it  can.  We  mean  to  imply  that  its  action  must  be 
rhythmic,  or  cease  entirely. 

ThB  ElTBCTS  OF  VaBIATIONS  IK  THK  ATMOSPHBBIO 

PBB88UBE. 

These  depend  in  great  part  upon  the  suddenness  with  which 
the  change  is  made.  When  an  individual  ascends  a  high 
mountain  or  rises  in  a  balloon,  parts  in  contact  with  the  air 
become  reddened  and  swollen,  owing  to  the  distention  of  the 
small  vessels,  which  may  result  in  heemorrhages.  There  is  dif- 
ficulty in  breathing,  the  respirations  become  more  rapid,  as  also 
the  pulse.  If  the  lowering  of  pressure  amounts  to  from  one 
third  to  one  half,  the  quantity  of  oxygen  in  the  blood  is  dimin- 
ished, and  the  carbon  dioxide  impeif  ectly  excreted.  Owing  to 
the  excess  of  blood  in  the  superficial  parts,  the  internal  organs 
become  ansBmic,  and  there  is  consequently  diminished  secretion 
of  urine  and  a  variety  of  other  disturbances,  with  general  weak- 
nes&    The  blood-pressure  is  also  altered. 

Sudden  diminution  of  pressure  gives  rise  to  a  liberation  of 
gas— chiefly  nitrogen— within  the  blood-vensels,  which  causes 
death  by  blocking  the  circulation  in  the  small  vessels  (hence 
also  the  danger  from  section  of  a  large  vein  in  surgical  opera- 
tions about  the  neck,  tilie  air  being  liable  to  be  sucked  in,  owing 
to  the  negative  pressure). 

Increase  in  the  atmospheric  pressure  when  not  very  great 
gives  rise  to  symptoms  akin  to  those  of  narcotic  poisoning; 
but  when  the  increase  amounts  to  twenty  atmospherei^  animals 
die,  as  if  asphyxiated,  with  convukdims.  Neither  the  assump-i 
tion  of  oxygen  nor  the  separation  of  carbon  dioxide  takes  place] 
to  the  usual  extent;  and  it  is  interesting  to  note  that  microV 
organisms  are  killed  under  similar  circumstances. 

With  considerable  diminution  of  pressure,  though  not  suf- 
ficient to  lead  to  a  fatal  result,  symptoms  the  opposite  of  those 
described  above  occur.  Thus,  there  is  paleness  of  the  surface, 
respiration  is  easy,  the  capacity  of  the  lungs  i^  increased,  owing, 
it  is  thought,  to  the  greater  descent  of  the  diaphragm,  in  con- 
sequence of  the  compression  of  tixe  gases  of  the  intestines. 


«wuyii'iwwW.' 


400 


ANIMAL  PHT8IOL0OT. 


Urine  is  secreted  in  excess,  there  is  more  muscular  energy,  and 
the  metabolism  of  the  body  generally  is  accelerated.  Air  under 
altered  pressure  has  been  employed  as  a  therapeutic  agent,  but 
a  little  reflection  will  make  it  clear  that  it  is  a  remedy  to  be 
used  with  the  greatest  care,  especially  when  there  is  disease  of 
the  heart,  blood-vessels,  etc. 


Thk  Influbncb  of  RmpnuTiOM  ok  ths  Oibculation. 

An  examination  of  tracings  of  the  intra-thoracic  and  blood- 
pressure,  taken  simultaneously,  shows  (1)  that  during  inspira- 
tion the  blood-pressure  rises  and  the  intra-thoracic  pressure 
falls ;  (2)  that  during  expiration  the  reverse  is  true ;  and  (8)  that 
the  heart-beat  is  slowed,  and  has  a  decided  effect  on  the  form 
of  the  pulse.  But  it  also  appears  that  the  period  of  highest 
blood-pressure  is  just  after  expiration  has  begun. 


Vto.  Its. 


totJmtmpmJtmr  iMHlnMtai  9mtm,jmA  thwatMrljr  aUka  m 


We  must  now  attempt  to  explain  how  these  changes  are 
brought  about  By  intra-thoracic  pressure  is  meant  the  press- 
ure the  lungs  exert  on  the  costal  pleura  or  any  organ  within 
the  chest,  which  must  differ  from  intra-pulmonary  pressure 
and  the  pressure  of  the  atmosphere,  because  of  the  resistance 
of  the  lungs  by  virtue  of  their  own  elasticity. . 

It  has  been  noted  that  even  in  death  the  lungs  remain  par- 
tially distended ;  and  ibhat  when  the  thorax  is  opened  the  pul- 
monary collapse  which  follows  demonstrates  that  their  elas- 
ticity amounts  to  about  five  millimetres  of  mercury,  which 
must,  of  course,  represent  but  a  small  portion  of  that  elasticity 
which  may  be  brought  into  play  when  these  organs  are  greatly 
distended,  so  that  they  never  press  on  the  costal  walls,  heart. 


nergy,  and 
Air  under 
I  agent,  but 
medy  to  be 
g  disease  of 


(JLATION. 

!  and  blood- 
ing inspira- 
sio  pressure 
uid  (2)  that 
m  the  form 
I  of  highest 


a.  Wood- 
cnrvoot  tato«- 


I  changes  are 
tnt  the  press- 
organ  within 
nary  pressure 
the  resistance 

s  remain  par- 
tened  the  pul- 
lat  their  elas- 
arcury,  which 
that  elasticity 
bus  are  greatly 
tl  walls,  heart. 


THB  BBSPIRATOBT  STSTEM. 


401 


etc.,  with  a  pressure  equal  to  that  of  the  atmosphere.  It  follows 
that  the  deeper  the  inspiration  the  greater  the  difference  be- 
tween the  intra-thoracio  and  the  atmospheric  pressure.  Even 
in  expiration,  except  when  forced,  the  intra-thoracic  pressure 
remains  less,  for  the  same  reason. 

These  conditions  must  have  an  influence  on  the  heart  and 
blood-vessels.  Bearing  in  mind  that  the  pressure  without  is 
practically  constant  and  always  greater  than  that  within  the 
thorax,  the  conditions  are  favorable  to  the  flow  of  blood  toward 
the  heart  As  in  inspiration,  the  pressure  on  the  great  veins 
and  the  heart  is  diminished,  and,  as  these  organs  are  not  rigid, 
they  tend  to  expand  within  the  thorax,  thus  favoring  an  on- 
ward flow.  But  the  opposite  effect  would  follow  as  regards  the 
large  arteries.  Their  expansion  must  tend  to  withdraw  blood. 
During  expiration  the  conditions  are  reversed.  The  effects  on 
the  great  veins  can  be  observed  by  laying  them  bare  in  the 
neck  of  an  animal,  when  it  may  be  seen  that  during  inspiration 
they  become  partially  collapsed,  and  refilled  during  expiration. 
In  consequence  of  the  marked  thickness  of  the  coats  of  the 
great  arteries,  the  effect  of  changes  in  intra-thoracic  pressure 
must  be  slight.  The  ccmi'paratively  thin-walled  auricles  act 
somewhat  as  the  veins,  and  it  is  likely  that  the  increase  of 
pressure  during  expiration  must  favor,  so  far  as  it  goes,  the 
cardiac  systole. 

More  blood,  then,  entering  the  right  side  of  the  heart  dur- 
ing inspiration,  more  will  be  thrown  into  the  systemic  circula- 
tion, unless  it  be  retained  in  the  lungs,  and,  unless  the  effect  be 
counteracted,  the  arterial  pressure  will  rise,  and,  as  all  the  con- 
ditions are  reversed  during  expiration,  we  look  for  and  find 
exactly  opposite  results.  The  lungs  themselves,  however,  must 
be  taken  into  the  account.  During  inspiration  room  is  pro- 
vided for  an  increased  quantity  of  blood,  the  resistance  to  its 
flow  is  lessened,  hence  more  blood  reaches  the  left  side  of  the 
heart  The  immediate  effect  would  be,  notwithstanding,  some 
diminution  in  the  quantity  flowing  to  the  left  heart,  in  conse- 
quence of  the  sadden  widening  of  the  pulmonary  vessels,  the 
reverse  of  which  would  follow  during  expiration;  hence  the 
period  of  highest  intra-thoracio  pressure  is  after  the  onset  of 
the  ex|Hratory  act  During  inspiration  the  descent  of  the  dia- 
phragm compressing  the  abdominal  organs  is  thought  to  forpe 
on  blood  from  the  abdominal  veins  int6  the  thoracic  vena  cava. 

That  the  respiratory  movements  do  exert  in  some  way  a 
pronounced  effect  on  tiie  circulati<m.  the  student  may  demon- 


4oa 


ANIMAL  PHYSIOLOi^r. 


Btrate  to  himself  in  the  following  ways :  1.  After  a  full  inspira- 
tion, close  the  glottis  and  attempt  to  expire  forcibly,  keeping 
the  fingers  on  the  radial  artery.  It  may  be  noticed  that  the 
pulse  is  modified  or  possibly  for  a  moment  disappears.  2.  Re- 
verse the  experiment  by  trying  to  inspire  forcibly  with  closed 
glottis  after  a  stropg  expiration,  when  the  pulse  will  again  be 
found  to  vary.  In  the  first  instance,  the  heart  is  comparative- 
ly empty  and  hampered  in  its  action,  intra-thoracic  pressure 
being  so  great  as  to  prevent  the  entrance  of  venous  blood  by 
compression  of  the  heart  and  veins,  while  that  already  within 
the  organ  and  returning  to  it  from  the  lungs  soon  passes  on 
into  the  general  system,  hence  the  pulseless  condition.  The 
explanation  is  to  be  reversed  for  the  second  case.  The  heart's 
beat  is  modified,  probably  reflexly,  through  the  cardlo-inhibitory 
center,  for  the  changes  in  the  pulse-rate  do  not  occur  when  the 
vagi  nerves  are  cut,  at  least  not  to  nearly  the  same  extent. 

OompantiTe.— It  may  be  stated  that  the  cardiac  phenomena 
referred  to  in  this  section  are  much  more  marked  in  some  ani- 
mals than  in  others.  Very  little  change  may  be  observed  in 
the  pulse-rate  in  man,  whUe  in  the  dog  it  is  so  decided  that  one 
observing  it  for  the  first  time  might  suppose  that  such  pro- 
nounced irregularity  of  tho  heart  was  the  result  of  disease ; 
though  even  in  this  animal  there  are  variations  in  this  respect 
with  the  breed,  age,  etc. 

We  must  now  direct  attention  to  certain  facts  which  have 
been  very  differently  interpreted. 

During  artificial  respiration,  when  air  is  pumped  into  the 
chest  by  a  bellows,  it  follows,  of  course,  that  all  the  usual  press- 
ure conditions  are  reversed—e.  g.,  the  inspiratory  pressure  is 
greater  than  the  expiratory. 

If  artificial  respiration,  in  an  animal  under  experiment,  be 
stopped,  it  may  be  noticed  that  there  is  at  first  a  steady  rise  of 
blood-pressure ;  but  presently  certain  undulations  in,  the  respir- 
atory tracings  may  be  observed,  known  as  I'raube-Hering 
curves ;  and  these  will  appear  even  when  the  vagi  nerves  are 
cut,  and  disappear  only  with  the  fall  of  blood-pressure  that 
ensues  with  the  exhaustion  of  the  animal. 

If  the  spinal  cord  has  been  divided,  the  tracings  may  still 
be  obtained,  though  the  effect  is  not  so  marked.  These  are  the 
phenomena,  but  there  is  much  divergence  of  opinion  as  to  their 
cause.  Some  maintain  that  mechanical  effects  suffice  to  explain 
them,  though  the  majority  are  not  of  this  opinion,  but  believe 
them  due  to  rhjrthmioal  variations  in  the  caliber  of  the  arteri- 


HMHMHIHMM^ 


isas— ..^-. 


■M\iiim)-mta::it:  r 


TH£  RESPIRATORY  SYSTEM. 


4m 


nil  inspira- 
ly,  keeping 
id  tUat  the 
irs.    2.  Re- 
with  closed 
ill  again  be 
>mparative- 
ic  pressure 
as  blood  by 
3ady  witbin 
Q  passes  on 
lition.    The 
The  heart's 
o-inhibitory 
iir  when  the 
extoit. 
phenomena 
in  some  ani- 
observed  in 
ded  that  one 
fct  such  pro- 
(  of  disease; 
L  this  respect 

» which  have 

iped  into  the 
5  usual  press- 
Y  pressure  is 

qteriment,  be 
steady  rise  of 
in^  the  respir- 
ratibe-Hering 
ji  nerves  are 
pressure  that 

ings  may  still 
These  are  the 
ion  as  to  their 
fBoe  to  explain 
>n,  but  believe 
?  of  the  arteri- 


oles affected  through  vaso-motor  nerves  in  obedience  to  the 
medullary  center  which  operates  by  their  agency;  and  that 


^^^•J?'*-r^5'*'*'^M  blood-OTMMDe  in  niMt  to  tlioir  Tnnb»-HMrii«  encna  (after  Foatw). 
yw.wM**  undulatloM  bdioM  Trmoiw Battag  cunca;  tboM  aatt  in  riat,  eOecta  of 
nqrintlaa;MidUMHniUlMt,oCtlwpiilw. 

when  this  center  is  disabled  its  subordinates  in  the  spinal  cord 
take  upon  them  the  task.  It  has  also  been  suggested  that  there 
may  be  a  local  vaso-motor  mechanism  acted  upon  by  the  ve- 
nous blood  or  that  the  muscle-cells  themselves  may  be  influ- 
enced by  the  unnatural  condition  of  the  blood  in  asphyxia. 

These  curves,  however,  also  appear  during  respiration  that 
deviates  but  little  from  the  normal. 

It  is  to  be  borne  in  mind  that  the  tracings  on  which  we 
have  based  our  reasoning  do  not  represoit  what  takes  place  in 
every  mode  of  breathing.  The  subject  is  one  of  great  com- 
plexity. Doubtless  mechanical  explanations  go  a  long  way 
here,  but  they  are  so  mixed  up  with  factors  that  play  a  part 
more  or  less  prominent,  though  difficult  to  isolate  in  individual 
instances,  and  in  no  wise  to  be  explained  as  other  than  vital 
effects,  that  one  must  exercise  the  usual  caution ;  the  more  so 
as  it  is  found  upon  actual  experiment  that  the  outcome,  as 
regards  bloofl-pressure,  is  not  always  quite  what  would  have 
been  expected,  reasoning  from  the  principles  of  physics  alone. 

That  there  are  rhythms  within  rhythms  in  the  vascular  an<] 
respiratory  system,  rendering  the  subject  complex  beyond  thej 
power  of  experiments  fully  to  unravel,  is  a  conviction  that  w^ 
think  will  deepen  in  the  minds  of  physiologists. 


ia>M»»»!i»iiri  wiliwtiWHKWiBiM 


V 


404 


ANIMAL  PHYSIOLOOr. 


The  Beipixfttioii  and  Cixeolatimi  in  Afphyxia.— A  most  in8truct-> 
ive  experiment  may  be  arranged  thus : 

Let  an  ansesthetized  rabbit,  cat,  or  such-like  animal,  have 
the  carotid  of  one  side  connected  with  a  glass  tube  as  before 
described  (page  229),  by  which  the  blood-pressure  and  its 
changes  may  be  indicated,  and,  when  the  normal  respiratory 
acts  have  been  carefully  observed,  proceed  to  notice  th»  effecto 
on  the  blood-pressure,  etc.,  of  pumping  air  into  the  chest  by  a 
bellows,  of  hindering  the  ingress  of  air  to  a  moderate  degree, 
and  of  struggling.  With  a  small  animal  it  will  be  difficult  to 
observe  the  respiratory  effects  on  the  blood-pressure  by  simply 
watching  the  oscillations  of  the  fluid  in  the  glass  tube,  but  this 
is  readily  enough  nuwle  out  if  more  elaborate  arrangements  be 
made,  so  that  a  graphic  tracing  may  be  obtained. 

But  the  main  events  of  asphyxia  may  be  well  (perhaps  best) 
studied  in  this  manner : 

Let  the  trachea  be  occluded  (ligatured).  At  once  the  blood- 
pressure  will  be  f^n  to  rise  and  remain  elevated  for  some  time, 
then  gradually  fall  to  zero.  These  changes  are  contemporane- 
ous with  a  series  of  remarkable  manifestations  of  disturbance 
in  the  respiratory  system  as  it  at  first  appears,  but  in  reality 
due  to  widespread  and  profound  nutritive  disturbance.  So  far 
as  the  breathing  is  concerned,  it  may  be  seen  to  become  more 
rapid,  deeper,  and  labored,  in  which  the  expiratory  phase  be- 
comes more  than  proportionably  marked  (dyspinoea) ;  this  is  fol- 
lowed by  the  gradual  a<ition  of  other  muscles  than  those  usually 
employed  in  respiration,  until  the  whole  body  passes  into  a  ter- 
rible convulsion— a  musolft^torm  in  consequence  of  a  nerve- 
storm.  When  this  has  lasted  a  variable  time,  but  usually 
about  one  minute,  there  follows  a  period  of  exhaustion,  during 
which  the  •subject  of  the  experiment  is  in  a  motionless  oondi* 
tion,.  interrupted  by  an  occasional  respiration,  in  which  inspi- 
ration is  more  pronounced  than  expirtftion ;  and,  finally,  the 
animal  quietly  stretches  every  limb^  the  sphincters  Are  rehixed, 
there  mcy  be  a  discharge  of  urine  or  fnces  from  peristaltic 
movements  of  the  bladder  or  intestines,  and  death  ehds  a  strik'- 
ing  scene.  These  events  may  be  dassified  in  three  stages, 
though  the  flrs^  and  lecond  especially  merge  into  one  another : 
h  Stage  of  dyspnoea.  2.  Stage  of  convulsions.  8.  Stage  of 
exhaustion. 

It  is  during  the  first  two  stages  that  the  blood-pressure  rises, 
and  during  the  third  that  it  sinks,  due  in  the  first  instance 
chiefly  to  excessive  activity  of  the  vaao-motor  center,  and  in 


^ 


I  itmWii 


fit  in8tracir> 

limal,  have 
)e  as  before 
tre  and  its 
respiratory 
9  th&  effects 
chest  by  a 
rate  degree, 
>  difficult  to 
e  by  simply 
ibe,  but  this 
igements  be 

lerhapsbest) 

;e  the  blood- 
r  some  time, 
atemporane- 
disturbance 
ut  in  reality 
mce.    So  far 
become  more 
ry  phase  be- 
);  thisisfol* 
those  usually 
les  into  a  ter- 
I  of  a  nerve- 
but  usually 
stion,  during 
ionless  oondi- 
which  inspi- 
U  floaUy,  the 
BMordaxed, 
»m  peristaltic 
,  ehds  a  strike 
three  stages, 
one  another : 
8.  Stage  of 

iressure  rises, 
first  instance 
tenter,  and  in 


THE  BBSPIBATORT  SYSTEM. 


405 


the  second  to  its  exhaustion  and  the  weakening  of  the  heart- 
beat. 

These  violent  movements  are  owing,  we  repeat,  to  the  action 
of  blood  deficient  in  oxygen  on  the  respiratory  center  (or  cen- 
ters), leading  to  inordinate  action  followed  by  exhaustion. 

iiie  duration  of  the  stages  of  asphyxia  varies  with  the  ani- 
mal, but  rarely  exceeds  five  minutes.  In  this  connection  it  may 
be  noted  that  newly-born  animals  (kittens,  puppies)  bear  im- 
mersiorf  in  water  for  as  much  as  from  thirty  to  fifty  minutes, 
while  an  adult  dog  dies  within  four  or  five  minutes.  This  is 
to  be  explained  by  the  feeble  metabolism  of  new-bom  mam- 
mals, which  so  slowly  uses  up  the  vital  air  (oxygen). 

If  the  chest  of  an  animal  be  opened,  though  the  respiratory 
muscles  contract  as  usual  there  is,  of  course,  no  ventilation  of 
the  lungs,  which  lie  collapsed  in  the'  chest;  and  the  animal  dies 
about  as  quickly  as  if  its  trachea  were  occluded.  It  passes 
through  all  the  phases  of  asphyxia  as  in  the  former  case ;  but 
additional  information  may  be  gained.  The  heart  is  seen  to 
beat  at  first  more  quickly  and  forcibly,  later  vigorously  though 
slower,  and  finally  both  feebly  and  irregularly,  till  the  ventri- 
cles, then  the  left  auricle,  and  finally  the  right  auricle  cease  to 
beat  at  all  or  only  at  long  intervals.  The  terminations  of  the 
great  veins  (representing  the  sinus  venosus)  beat  last  of  alL 

At  death  the  heart  and  great  veins  are  much  distended 
with  blood,  the  arteries  comparatively  empty.  Even  after 
rigor  mortis  has  set  in,  the  right  heart  is  still  much  engorged. 

These  phenomena  are  the  result  of  the  operation  oi*  several 
causes.  The  increasingly  venous  blood  at  first  stimulates  the 
heart  probably  directly,  in  part  at  least,  but  later  has  the  con- 
trary effect.  The  nutrition  of  the  organ  suffers  from  the  de- 
graded blood,  from  which  it  must  needs  derive  its  supplies. 
The  caiitO'inhibitory  center  probably  has  a  large  share  in  the 
slowing  of  the  heart,  if  not  also  in  quickening;  it  Whether 
the  accelerator  fibers  of  the  vagus  or  sympathetic  play  any 
part  is  uncertain.  The  increase  of  peripheraT  resistance  caused 
by  the  action  of  the  vaso-mot6r  center  makes  it  more  difficult 
for  the  heart  to  empty  its  left  side  and  thus  receive  the  venoua 
blood  as  it  pours  on.  At  the  same  time  the  deep  inspirations 
(when  the  chest  is  unopened)  favor  the  onflow  of  venous  blood; 
and  in  any  case  the  whole  venous  system,  including  the  right 
heart,  tends  to  become  engorged  from  these  several  causes  act- 
ing together.  The  heart  gives  up  the  struggle,  unable  to  main- 
tain it,  but  not  so  long  as  it  can  beat  in  any  part. 


mmmmmmmi0 


406 


ANIMAL  PHTSIOLOGT. 


The  share  which  the  elasticity  of  the  arteries  takes  in 
forcing  on  the  blood  when  the  heart  ceases,  and  the  contraction 
of  the  muscular  coat  of  these  vessels,  especially  the  smaller, 
must  not  be  left  out  of  the  account  in  explaining  the  phenom- 
ena of  asphyxia  and  the  post-mortem  appearances. 

FathologiiML — ^The  importance  of  being  practically  as  well  as 
theoretically  acquainted  with  the  facts  of  asphyxia  is  very  great. 

The  appearance  of  the  heart  and  venous  system  gives  une- 
quivocal evidence  as  to  the  mode  of  derth  in  any  casb  of  as- 
phyxia; and  the  contrast  between  the  heart  of  an  animal  bled 
to  death,  or  that  has  died  of  a  lingering  disease,  and  one 
drowned,  hanged,  or  otherwise  asphyxiated,  is  extreme. 

We  strongly  recommend  the  studeni;  to  asphyxiate  some 
small  mammal  placed  under  the  influence  of  an  ansesthetic, 
and  to  note  the  phenomena,  preferably  with  the  chesi  opened ; 
and  to  follow  up  these  observations  by  others  after  the  onset 
of  rigor  mortis. 

Pecuuar  Respiratort  Movbmbnts. 

Though  at  first  sight  these  seem  so  different,  and  are  so  as 
regards  acts  of  expression,  yet  from  the  respiratory  point  of 
view  they  resemble  each  other  closely;  they  are  all  reflex, 
and,  of  course,  involuntary.  Many  of  them  have  a  common 
purpose,  either  the  better  to  ventilate  the  lungs,  to  clear  them 
of  foreign  bodies,  or  to  prevent  their  ingress. 

Cotighing,  in  which  such  a  purpose  is  evident,  is  made  up  of 
several  expiratory  efforts  preceded  by  an  inspiratory  act.  The 
afferent  nerve  is  usually  the  vagus  or  laryngeal,  but  may  be 
one  or  more  of  several  others. 

The  glottis  presents  characteristic  appearances,  being  closed 
and  then  opened  suddenly^  the  mouth  being  kept  opisn. 

Coughing  is  often  induced  in  attempting  to  examine  the  ear 
with  instruments.    (Reflex  act.) 

Laughing  is  very  similar  to  the  last,  so  far  as  the  behavior 
of  the  glottis  is  concerned,  though  it  usually  acts  more' rapidly, 
of  course.    Several  expirations  follow  a  deep  inspiration. 

Crying  is  essentially  the  same  as  laughing,  but  the  facial 
expression  is  different,  and  the  lachrymal  gland  functions  exces- 
sively, though  with  some  persons  this  occurs  during  laughter 
also. 

ScMnng  is  made  up  of  a  series  of  inspirations,  in  which  the 
glottis  is  partially  closed,  followed  by  a  deep  expiration. 


M>«wMaKMiltellMMflMliiwn>i 


litMiMWiiUilii 


3  takes  in 
sontraction 
le  smaller, 
le  phenom- 

r  as  well  as 
very  great, 
gives  une- 
casb  of  as-  . 
nimal  bled 
e,  and  one 
me. 

xiate  some 
aneesthetic, 
)si  opened; 
ir  the  onset 


d  are  so  as 
ry  point  of 
I  all  reflex, 
a  common 
)  clear  them 

made  np  of 
•y  act.  The 
but  may  be 

being  closed 

pen. 

nine  the  ear 

the  behavior 
lore' rapidly, 
■alion. 

it  the  facial 
ctions  exces- 
ng  laughter 


n  which  the 


THB  BBSPIBATOBT  STSTBM. 


407 


Yawning  involves  a  deep-drawn,  slow  inspiration,  followed 
by  a  more  sudden  expiration,  with  a  well-known  depression  of 
the  lower  jaw  and  usually  stretching  movements. 

Sighing  is  much  like  the  preceding,  though  the  mouth  is  not 
opened  widely  if  at  all,  nor  do  the  stretching  movements  com- 
monly occur. 

Hieeough  is  produced  by  a  sudden  inspiratory  effort,  though 
fruitless,  inannuch  as  the  glottis  is  suddenly  closed.  It  is 
spoken  of  as  spasm  of  the  diaphragm,  and  when  long  continued 
is  very  exhaustive. 

Sneezing  is  the  result  of  a  powerful  and  sudden  expiratory 
act  following  a  deep  inspiration,  the  moutii  being  usually  closed 
by  the  anterior  pillars  of  the  fauces  against  the  outgoing  cur- 
rent of  air,  which  then  makes  its  exit  through  the  nose,  while 
the.  glottis  is  forcibly  opened  after  sudden  closure.  It  will  be 
noticed  that  in  most  of  theao  acts  the  glottis  is  momentarily 
closed,  which  is  never  the  case  in  mammals  during  quiet  res- 
piration. 

This  temporary  occlusion  of  the  respiratory  passages,  per- 
mits of  a  higher  intrapulmonary  pressure,  which -is  very  effect- 
ive in  clearing  the  passages  of  excess  of  muctis,  etc.,  when  the 
glottis  is  suddenly  opened.  Though  the  acts  described  are  all 
involuntary,  they  may  most  of  tiiem  be  imitated  and  thus 
studied  deliberately  by  the  studout.  It  will  also  appear,  con* 
sidering  the  many  ways  in  which  some  if  not  all  of  them  may 
be  brought  about,  that  if  the  medullary  center  is  responsible 
for  the  initiation  of  tiiem,  it  must  be  accessible  by  numberless 
paths. 

OoapanttTa.— Few  of  the  lower  animals  cough  with  the  same 
facility  as  man,  while  laughing  is  all  but  unknown,  crjring  and 
sobbing  rare,  though  the  whining  of  dogs  is  allied  to  the  cry- 
ing of  human  beings. 

Sneesing  seems  to  be  voluntary  in  some  animals,  as  squir- 
rels, when  engaged  in  toilet  operations,  etc. 

Barking  is  voluntary,  and  in  mechanism:  resembles  cough- 
ing, the  voci^  cords  being,  however,  more  definitely  employed, 
as  also  in  growling. 

Bawling,  neighing,  braying,  etc.,  are  made  up  of  long  expira- 
tory acts,  preceded  by  one  or  more  inspirations.  The  vocal 
coids  are  aliso  rendered  tense. 


mmiiMttmMtatMmMm.mi>tiumut«mmiimmtiim> 


408 


ANI2IAL  PHYSIOLOGY. 


Special  Considerations. 

Pathologioal  ud  GUnieaL— The  number  of  diseases  that  lessen 
the  amount  of  available  pulmonary  tissue,  or  hamper  the  move- 
ments of  the  chest,  are  many,  and  only  the  briefest  reference 
can  be  made  to  a  few  of  them. 

Inflammation  of  the  lungs  may  render  a  greater  or  less  por- 
tion of  one  or  both  lungs  solid ;  inflammation  of  the  jAewra 
(pleuritis,  pleurisy)  by  the  drjmess,  pain,  etc.,  may  restrict  the 
thoracic  movements;  phthisis  may  solidify  or  excavate  the  lungs, 
or  by  pleuritic  inflammation  glue  the  costal  and  pulmonary 
pleural  surfaces  together;  bronchitis  clog  the  tubes  and  other 
air-passages  with  altered  secretions ;  emphysema  (distention  of 
air-cells)  may  destroy  elasticity  of  parts  of  the  lung;  pneumct- 
thorax  from  rupture  of  the  lung-tissue  and  consequent  accumu- 
lation of  gases  in  the  pleural  cavity,  or  pleurisy  with  effusion, 
render  one  lung  all  but  useless  from  pressure.  In  all  such 
cases  Nature  attempts  to  make  up  what  is  lost  in  amplitude  by 
increase  in  rapidity  of  the  respiratory  movements.  It  is  inter- 
esting to  note  too  how  the  other  lung,  in  diseased  conditions,  if 
it  remain  unaffected,  enlarges  to  compensate  for  the  loss  on  the 
opposite  side.  When  the  muscles  are  weak,  especially  if  there 
be  hindrance  to  the  entrance  of  air  while  the  thoracic  move- 
ments are  marked,  there  may  be  bulging  inward  of  the  inter- 
costal spaces. 

Normally,  this  would  also  occur,  as  the  intra-thoracic  press- 
tire  is  less  than  the  atmospheric,  were  it  not  for  the  fact  that 
the  intercostal  muscles  when  contracting  have  a  certain  resist- 
ing power. 

The  imperfect  respiration  of  the  moribund,  permitting  the 
/accumulation  of  carbonic  anhydride  with  its  soporific  effects, 
smooths  the  descent  into  the  valley  of  the  shadow  of  death ;  so 
that  there  may  be  to  the  uninitiated  the  appearance  of  a  suffer- 
ing which  does  not  e^st,  consciousness  itself  bemg  either 
wholly  or  partially  absent.  The  dyspnoea  of  anemic  jwrsons, 
whether  from  sudden  loss  of  blood  or  from  imperfect  )rmiewal 
of  the  haemoglobin,  shows  that  this  substance  has  a  respiratory 
function;  while  informs  of  cmrdiac  disease  with  regurgitation, 
etc.,  the  blood  may  be  imperfectly  oxidised,  pdviag  rise  to  la- 
bored respiration. 

Penonal  Obiimit|oin.-~As  hinted  from  time  to  time  during 
the  treatment  of  this  subject,  there  is  a  large  number  of  facts 
the  student  may  verify  for  himself. 


MitaiiiMiHMMMlWMin 


<>mm 


»MMP 


THE  BBSPIRATORT  SYSTEM. 


409 


that  lessen 

the  move- 

;  reference 

>r  less  por- 
the  pleura 
estrict  the 
9  the  lungs, 
pulmonary 
i  and  other 
stention  of 
;;  pnewna- 
at  accumu- 
th  efiFusion, 
11  all  such 
iplitude  by 

It  is  inter- 
tnditions,  if 

loss  on  the 
lly  if  there 
•acic  move* 
{  the  inter* 

traoic  press- 
le  fact  that 
rtainresist- 

mitting  the 
»rific  effects, 
)f  death ;  so 
)  of  a  snffer- 
leiiQg  either 
nio  persons, 
feet  )miewal 
^respiratory 
gurgitation, 
ig  rise  to  la- 
time  during 
iher  of  facts 


A  simple  way  of  proving  that  CO.  is  exhaled  is  to  bi-eathe 
(blow)  into  a  vessel  containing  some  clear  solution  of  quick- 
lime (CaO),  the  turbidity  showing  that  an  insoluble  salt  of  lime 
(GaCOa)  has  hem  formed  by  the  addition  of  this  gas. 

The  functions  of  most  of  the  respiratory  muscles,  the  phe- 
nomena of  dyspnoea,  apnoea  (by  a  series  of  long  breaths),  partial 
asphyxia  by  holding  the  breath,  and  many  other  experiments, 
simple  but  convincing,  will  occur  to  the  student  who  is  willing 
to  learn  in  this  way. 

The  observation  of  respiration  in  a  dreaming  animal  (dog) 
wiQ  show  how  mental  occurrences  affect  the  respiratory  center 
in  the  absence  of  all  the  usual  outward  influmices.  The  respira- 
tion of  the  domestic  animals,  of  tl-  r  og,  turtle,  snake,  and  fish 
are  easily  watched  if  these  cold-b.c  jded  animals  be  placed  for 
observation  beneath  a  glass  vessel  Their  study  will  teach  how 
manifold  are  the  ways  by  which  the  one  end  is  attained.  Com- 
pare the  tracings  of  Fig.  313. 

IfdutiOB. — ^A  study  of  embryology  shows  that  the  respirsr 
tory  and  circulatory  systems  d^lop  together;  that  the  vascu- 
lar system  functions  largely  a/a  respiratory  system  also  in  cer- 
tain stages,  and  remains  such,  from  a.  physiological  point  of 
view,  throughout  embryonic  life. 

The  changes  that  take  place  in  the  vascular  system— the 
heart,  especially— of  the  mammal  when  the  lungs  have  become 
functionally  active  at  birth,  show  how  one  set  of  organs  modi- 
fies the  other. 

When  one  considers,  in  addition  to  tibese  facts,  that  the 
digestive  as  well  as  the  vascular  and  respiratory  organs  are 
represented  in  one  group  of  structures  in  a  jelly-fish,  and  that 
the  lungs  of  the  mammal  are  derived  from  tiie  same  mesoblast 
as  gives  rise  to  the  digestive  and  circulatory  organs,  many  of 
the  relations  of  these  systems  in  the  highest  groups  of  animals 
become  intelligible;  but  unless  there  be  descent  with  modifica- 
tion, these  facts,  clear  enough  from  an  evolutionary  standpoint, 
are  isolated  and  out  of  joint,  bound  together  by  no  common 
principle  that  satisfies  a  philosophical  biology. 

It  has  been  found  that  in  hunting-dogs  and  wild  rabbits  the 
vagus  is  more  efficient  than  in  other  races  of  dogs  and  in  rab- 
bits kept  in  confinement ;  and  pomibly  this  inay  in  part  account 
for  the  greater  speed  and«  especially  the  endurance  of  the 
former.  The  very  conformation  of  some  animals,  as  the  grey- 
hound, with  his  deep  chest  and  capacious  lungs,  indicates  an 
unusual  respiratory  capacity. 


■\)i&m0tae»vimn9mtmUHi 


iiinitliitiiiliili 


oAivtl^ 


410 


ANIMAL  PHYSIOLOOT. 


The  law  cf  habU  is  well  illustrated  in  the  case  of  divers,  who 
can  bear  deprivation  of  air  longer  than  those  unaccustomed  to 
such  submersion  in  water.  Oreater  toleration  on  the  part  of 
the  respiratory  center  has  probably  much  to  do  with  the  caee, 
though  doubtless  many  other  departures  from  the  normal  occur, 
either  independently  or  correlated  to  the  changes  in  the  respin^ 
tory  center. 

luuuury  of  Am  VbjtUlogj  flf  BMpintioB.— The  purpose  of 
repiration  in  all  animals  is  to  furnish  oxygen  for  the  tissues 
and  remove  the  carbonic  anhydride  they  produce,  which  in  all 
vertebrattf  is  accomplished  by  t^ie  exposure  of  the  blood  in 
capillaries  io  thn  ^^^iscspheriu  air,  either  free  or  dissolved  in 
water.  A  membrane  lined  with  cells  always  intervenes  between 
the  capillaries  and  the  air. 

The  air  may  be  pumped  in  and  out,  or  sucked  in  and  forced 
out. 

Xtsplntiini  ia  the  Wawwai— The  air  enters  the  lungs,  owing 
to  the  enlargement  of  the  chest  in  three  directions  by  the  action 
of  certain  muscles.  It  leaves  the  lungs  because  of  thjeir  own 
elastic  recoil  and  that  of  the  chest-wall  chiefly.  Inspiration  is 
active,  expiration  chiefly  passive. 

The  diaphragm  is  the  principal  muscle  of  respiration.  In 
some  animals  there  is  a  well-marked  facial  and  laryngeal  as 
well  as  thoracic  respiration.  Respiration  is  rhythmical,  con- 
sisting of  inspiration,  succeeded  without  appreciable  pause  by 
expiration,  the  latter  being  in  health  of  only  slightly  longer 
duration.  There  is  also  a  definite  relation  between  the  number 
of  respirations  and  of  heart-beats.  According  as  respiration  is 
normal,  hurried,  labored,  or  interrupted,  we  describe  it  as 
eupnoM,  hyperpncea,  dyapnim,  and  apncM.  The  intra-thoracic 
pressure  is  never  equal  to  the  atmospheric— -i.  e.,  it  is  always 
negative— except  in  forced  expiration ;  and  the  lungs  are  never 
collapsed  so  long  as  the  chest  is  unopened.  The  expired  air 
differs  from  that  inspired  in  being  of  the  temperaiture  of  the 
body,  saturated  with  moisture,  and  containing  about  4  to  6 
per  cent  less  oxygen  and  4  per  cent  more  carbonic  anhydride, 
besides  certain  indifferently  known  bodies,  the  result  of  tissue 
metabolism,  excreted  by  the  lungs. 

The  quantity  of  iair  actually  moved  by  a  respiratory  act,  as 
compared  with  the  total  capacity  of  the  respiratory  organs,  is 
smaU ;  hence  a  great  jmrt  nmst  be  played  by  diffusion.  The 
portion  of  air  that  can  not  be  removed  from  the  lungs  by  any 
respiratory  effort  is  relatively  large. 


i\timt»M'MMmi 


■M«»i««««**»*l(aBMPW»*»ls^W . ' 


THE  BBSPIBATORT  SYSTEM. 


411 


iver8,wlio 
Lstomed  to 
he  part  of 
the  cmk9, 
rmal  occur, 
heTespyr»> 

ptirpoee  of 
the  tissaes 
hich  in  all 
e  blood  in 
isBolved  in 
les  between 

and  forced 

ingB,  owing 
7  the  action 
f  their  own 
uspiration  is 

liration.  In 
aryngeal  as 
kimioal,  con- 
>le  pause  by 
jhtly  longer 
the  number 
espiration  is 
iscribe  it  as 
itra-thoracic 
it  is  always 
Lgs  are  never 
I  expired  air 
ratnre  of  the  , 
kbout  4  to  5 
ic  anhydride, 
rait  of  tiflsae 

ratory  act,  as 
nry  organs,  is 
ffosion.  The 
lungs  by  any 


It  is  customary  to  distinguish  tidal,  complementary,  supple- 
mentary, and  residual  air. 

The  vital  capacity  is  estimated  by  the  quantity  of  air  the 
respiratory  organs  can  move,  and  is  very  variable. 

The  blood  is  the  respiratory  tissue,  through  the  mediation 
of  its  red  cells,  by  the  heemoglobin  they  contain.  This  sub- 
stance is  a  ferruginous  proteid,  capable  of  crystallisation,  and 
assuming  under  chemical  treatment  many  modifications.  When 
it  coixUuns  all  the  oxygen  it  can  retain,  it  is  said  to  be  saturated, 
and  is  called  oxy -heemoglobin,  in  which  form  it  exists  (with 
some  reduced  heemoglobin)  in  arterial  blood,  and  to  a  lesser 
extent  in  venous  blood,  which  differs  from  arterial  in  the  rela- 
tive proportions  of  heemoglobin  (reduced)  it  contains,  as  viewed 
from  the  respiratory  standpoint. 

Oxy-heemoglobin  does  not  assume  or  part  with  its  oxygen, 
according  to  the  Heury-Dalton  law  of  pressures,  nor  is  this  gas 
in  a  state  of  ordinary  chemical  combination.  It  is  found  that 
the  oxygen  tension  of  the  blood  is  lower  and  that  of  carbonic 
anhydride  higher  than  in  the  air  of  the  alveoli  of  the  lungs, 
while  the  same  may  be  said  of  the  tissues  and -the  blood  re- 
spectively.   This  has  been-,  however,  recently  again  denied. 

Respiration  is  a  vital  process,  though  certain  physical  con- 
ditions (temperature  and  pressure)  must  be  rigidly  maintained 
in  order  that  the  gaseous  interchanges  shall  take  place.  Res- 
piration is  always  fundamentally  bound  up  with  the  metabo- 
lism of  the  tissues  themselves.  All  animal  cells,  whether  they 
exist  as  unicellular  animals  (Amoeba)  or  as  the  components  of 
complex  organs,  use  up  oxygen  and  produce. carbonic  dioxide. 
Respiratory  organs,  usually  so  called,  and  the  respiratory  tissue 
par  exetiBence  (the  blood)  are  only  snppleihentaiy  mechanisms 
to  facilitate  tissue  respiration.  C-rbonic  anhydride  exists  in 
blood  probably  in  combination  with  sodium  salts,  though  the 
whole  matter  is  very  obscure. 

Respiration,  like  all  the  other  functions  of  the  body,  is  con- 
trolled by  the  central  nervous  system  thrdugh  nerves.  The 
medulla  oblongata  is  chiefly  concerned,  and  especially  one 
small  pari;  of  it  known  as  the  respiratory  center.  It  is  possi- 
ble, even  probable,  that  there  are  subordinate  centers  in  the 
ooid,  which,  under  peculiar  circumstances,  assume  importance; 
but  how  far  they  act  in  concert  with  the  medullary  center,  oil 
whether  they  act  at  all  wheia  normal  conditions  prevail,  is  aiv 
open  question. 

The  vagus  is  the  principal  afferent  respiratory  nerve.    The 


*is:tiyv<rint^mavmi»miiiiammi 


am 


41i 


ANIMAL  PHTSIOLOOT. 


efferent  nerves  are  the  phrenics,  intercostals,  and  others  supply- 
ing the  various  muscles  used  in  moving  the  chest-walls,  etc. 

The  respiratory  center  is  automatic,  hut  its  action  is  sus- 
ceptible of  modification  through  afferent  influences  taking  a 
variety  of  paths.  The  respiratory,  vaso-motor,  and  cardio- 
inhibitory  centers  seem  to  act  somewhat  in  concert. 

Blood-pressure  is  being  constantly  modified  by  the  respira- 
tory act,  rising  with  inspiration  uid  sinking  with  expiration. 
In  some  animals  the  heart-beat  also  varies  with  these  phases 
of  respiration,  becoming  slow  and  irregular  during  expiration. 
Into  the  causation  of  these  changes  both  mechanical  and  nerv- 
ous factors  enter,  and  make  a  very  complex  mesh,  which  we 
can  at  present  but  imperfectly  unravel.  When  the  access  of 
j  air  to  the  tissues  is  prevented,  a  series  of  stages  of  respiratory 
activity  and  decline,  accompanied  by  pronounced  changes  in 
the  vascular  system,  are  passed  through,  known  as  asphyxia. 

Three  stages  are  distinguishable:  one  of  dyspnoea,  one  of 
convulsions,  and  one  of  exhaustion — ^while  at  the  same  time 
there  is  a  rise  of  blood-pressure  during  the  first  two,  and  a 
decline  during  the  third,  accompanied  by  marked  alterations  in 
the  cardiac  rhythm. 


^>BOTECTIVE  AND  EXCBXTOBT  FUNCfTIONS  OF  THE  SKIN. 

As  has  been  intimated  from  time  to  time,  thus  far,  as  a 
result  of  the  metabolism  of  the  tissues,  certain  products  require 
constant  removal-  from  the  blood  to  prevent  poisonous  effects. 
These  substances  are  in  all  probability  much  more  numerous 
than  physiological  chemistry  has  as  yet  distinctly  recognized 
or,  at  all  events,  isolated.  Quantitatively  considered,  the  niost 
important  are  oarbonio  anhydride,  water,  urea»  and,  of  less  im- 
portance, perhaps,  certain  salts. 

In  many  invertebrates  and  in  all  vertebrates  several  organs 
take  part  in  this  work  of  elimination  of  waste  products  or  puri- 
fication of  the  blood,  one  set  of  which— the  respiratory — ^we 
have  just  studied ;  and  we  now  continue  the  consideration  of 
the  subject  of  excretion,  this  term  being  reserved  for  the  pro- 
cess of  separating  harmful  products  from  the  blood  and  dis- 
charging them  from  the  body. 

We  strongly  reeommend  the  student  to  make  the  study  of 
excretion  comparative  in  the  sense  of  noting  how  one  organ 
engaged  in  the  process  sujyplements  auother.    A  clear  under- 


^    .- 


PROTECTIVE  AND  EXCRBTORY  FUNCTIONS  OP  THE  SKIN.  418 


re  snpply- 
lls,  etc. 
on  is  BU8- 
i  taking  a 
id  cardio- 

\ie  respira- 
jxpiration. 
Bse  phases 
expiration.       < 
i  and  nerv- 
,  which  we 
)  access  of 
respiratory     • 
changes  in 
«phyxia. 
oea,  one  of 
same  time 
two,  and  a 
derations  in 


THE  SKIN. 

IS  far,  as  a 
acts  require 
ions  effects. 
9  numerous 
'recognized 
ad,  the  ihost 
,  of  less  im- 

reral  organs 
ticts  or  puri- 
liratory — ^we 
ideration  of 
for  the  pro- 
x)d  and  dis- 

the  study  of 
vr  one  organ 
clear  under- 


standing of  this  relation  even  to  details  makes  the  practice  of 
medicine  more  scientific  and  practically  effective,  and  gives 
physiology  greater  breadth. 

The  skin  has  a  triple  function :  it  is  protective,  excretory, 
sensory,  and,  we  may  udd,  nutritive  (absorptive)  and  respira- 
tory, especially  in  some  groups  of  animals. 

As  a  sensory  organ,  the  skin  will  receive  attention  later. 
Proksetiv*  Foafltiim  of  th«  lkla.—Gomp«nkiTe.— Among  many 
groups  of  invertebrates  the  principal  use  of  the  exterior  cover- 
ing of  the  body  ia  manifestly  protection.  Among  these  forms, 
an  internal  skeleton  being  absent,  the  exo-skeleton  is  developed 
externally,  and  serves  not  only  for  protection,  but  for  the  at- 
tachment of  muscles,  as  seen  in  crustaceans  and  insects.  But 
this  part  of  the  subject  is  too  large  for  detailed  treatment  in 

such  a  work  as  this.  Turning  to 
the  vertebrates,  we  see  scales, 
bony  plates,  feathers,  spines,  hair, 
etc.,  most  of  them  to  be  regarded 
as  modifications  of  the  epidermis, 
always  useful,  and  frequently  also 
i^^^^^^^^^^^^H  omammtal. 
'^^^^^^H^^^Hi  Primitive  man  was  probably 

much  more  hin; ate  than  his  mod- 


FM. 


Km.  an.-SiMlof4wrmM  |l«adB.   1 »  «>  (After  Sqpiwjr.)  lJi.„^._^     . 
V»mL—Maim«rSlaat  imim  at  hMid  •book  oiwlHilf  m  tatk 


iW 


(After  84i«^>   1>  !•  >•  ^  <V«^BR*  << 


.excrrtonr 


Iii4. 


Mdoriteoaidaate:  a,  9,  a.  a,  groovM  between 


em  representative;  and,  though  the  human  snbjeot  is  at  prea- 
ent  provided  with  a  skin  in  which  protective  functions  are  at 
their  lowest,  still  the  epidermis  does  serve  such  a  purpose,  as 


tmtmma  n't* 


■»»pii»HHMWwt'*M)  Jiww*i^"iiwwai'w  \itm  u. 


4U 


ANIMAL  PHYSIOLUOY. 


IV 


all  Lave  some  time  realized  when  it  has  been  accidentally  re- 
moved by  blistering,  etc. 

Taking  the  structure  of  the  skin  of  man  as  representing  that 
of  mammals  generally,  certain  points  claim  attention  from  the 

physiologist.  Its  elastic- 
ity, the  failure  of  which 
in  old  age  accounts  for 
wrinkles;  its  epidermal 
covering,  made  up  of 
numerous  layers  of  cells ; 
its  coiled  and  spiral- 
ly twisted  sudoriferous 
glands,  permitting  of 
movements  of  the  skin 
without  harm  to  these 
structures ;  its  hair-folli- 
cles and  associated  seba- 
ceous glands,  the  fatty 
secretion  of  which  keeps 
the  hair  and  the  skin  gen- 
erally soft  and  pliable. 

The  muscles  of  the 
skin,  which  either  move 
it  as  a  whole  or  erect  in- 
dividual hairs,  play  an 
important  part  in  modi- 
fying expression,  well 
seen  in  the  whole  canine 
tribe  and  many  others. 

There  are  several  mod- 
ificaticms  of  the  sebaceous 
glands  that  furnish  high- 
ly odoriferous  secretions, 
as  in  the  civet  cat,  the 
skunk,  the  musk  -  deer, 
and  many  lower  verte- 
brates. In  some,  these 
are  protective  (skunk) ; 
in  others,  though  they 
may  not  be  agreeable  to 
the  senses  of  man,  they  are  doubtless  attractive  to  the  females 
of  the  same  tribe,  and  are  to  be  regarded  as  important  in 
"  sexual  selection,"  being  often  confined  to  the  males  alone. 


fra 


m-H«lr  and  hair-foUiele  (•flOT  Sapper).    1. 
root  of  hair  :  S,  bulb  of  J"?" '.„?i'"*w»'  »«*• 
■heath;  B,  tUHMruub at  hair-foUieto : 
niMBbnuie  o*  foUlde;  7,7.  mwoidL 

■bnpie  MbaoBoS  gbwd;  It,  opminc  o(  hab^fol- 


CaxMnMa 
rbaatoat- 


MMoMi 


MWWft'iSwM 


PROTECTIVE  AND  EXCRETORY  FUNCTIONS  OP  THE  SKIN.  415 


entally  re- 

inting  that 
from  the 
Its  elastic- 
of  which 
sounts  for 
epidermal 
ie    up    of 
rs  of  cells ; 
id    spiral- 
idoriferous 
itting     of 
the  skin 
to   these 
halr-foUi- 
iated  seba- 
the  fatty 
bich  keeps 
e  skin  gen- 
pliable, 
es   of   the 
ther  move 
r  erect  in- 
i,  play  an 
t  in  modi- 
Bion,    well 
iiole  canine 
r  others, 
iveral  mod- 
d  sebaceous 
mish  high- 
secretions, 
et  cat,  the 
lusk  -  deer, 
wer   verte- 
ome,  these 
)   (skunk) ; 
ough   they 
greeable  to 
the  females 
iportant  in 
8  alone. 


Ear-wax  and  the  Meibomian  secretion  are  the  work  of  modi- 
fled  sebaceous  glands ;  as  also  the  oil-glands  so  highly  developed 
in  birds,  especially  aquatic  forms,  of  which  these  creatures 
make  great  use  in  preserving  their  feathers  from  wotting. 

Thb  Excretory  Function  of  the  Skin. 

Sweating  in  man  has  been  studied  by  inclosing  the  greater 
part  of  the  body  or  a  single  limb  in  a  caoutchouc  or  other  form 
of  impermeable  covering  and  exposing  the  subject  to  various 
degrees  of  heat;  but,  apart  from  errors  in  collecting, weighing, 
etc.,  such  sweating  must  be  regarded  as  somewhat  abnormal. 

It  is  clear,  however,  that  the  quantity  of  matter  discharged 
through  the  skin  is  large— greater  than  by  the  lungs  (about  as 
7  to  11),  though  the  amount  is  very  variable,  depen(?ing  on 
the  degree  of  activity  of  other  related  >ixcreting  organs,  ?w  the 
lungs  and  kidneys,  and  largely  upo'  the  teinperatuve  as  a 
physical  condition. 

When  the  watery  vapor  is  carried  off,  befc  o  it  c  *n  condense, 
the  perspiration  is  said  to  be  inaenaible  :  when  «mall  droplets 
become  visible,  aenaOtAe.  As  to  whether  the  ono  or  the  ;i,her 
is  predominant  will,  of  course,  depend  on  the  rapidity  ;  re- 
newal of  the  air,  its  humidity,  and  its  temperature,  impart 
from  the  temperature,  the  amount  of  sweat  is  i  1  vs  need  by  the 
quality  and  quantity  of  food  and,  especially  of  <  nnk  taken, 
the  amount  of  exercise,  and  psychic  conditions ;  not  to  speak 
of  the  effect  of  drugs,  poisons,  or  disease. 

Perspiration  in  man  is  a  clear  fluid,  mostly  colorless,  with 
a  characteristic  odor,  devoid  of  morphological  elements  (except 
epidermal  scales),  and  alkaline  in  reaction.  It  may  be  acid 
from  the  admixture  of  the  secretion  of  the  sebaceous  glanda 

Its  solids  (less  than  2  per  cent)  consist  of  sodium  salts, 
mostly  chlorides,  cholesterin,  neutral  fats,  and  traces  of  urea. 
The  acids  of  the  sweat  belong  to  the  fatty  series  (acetic,  buty- 
ric, formic,  propionic,  caprylic,  caproic,  etc.).' 

FttttoliOglML— The  sweat  may  contain  blood,  proteids,  abun- 
dance of  urea  (in  cholera),  uric  aovj,  xalates,  sugar,  lactic  acid, 
bile,  indigo  and  other  pigments.  Aany  medicines  are  elnii- 
nated  in  part  through  the  skiiu 

■•qinliMi  1^  tlM  SkiL— Ctmpazatif*.— In  reptiles  and  batra- 
chians,  with  smooth,  moist  ukin,  the  respiratory  functions  of 
this  organ  are  of  greal<  importance;  hence  these  animals  can 
live  long  under  water. 


416 


ANIMAL  PHTSI0L0G7. 


It  is  estimated  that  in  the  frog  the  greater  part  of  the  car- 
bonic anhydride  of  the  body- waste  is  eliminated  by  the  skin. 
Certainly  frogs  can  live  for  days  immersed  in  a  tank  supplied 
with  ninning  water ;  and  it  is  a  significant  fact  that  in  this 
animal  the  vessel  that  gives  rise  to  the  pulmonary  art«ry  sup- 
plies also  a  cutaneous  branch. 

The  respiratory  capacity  of  the  skin  in  man  and  most  mam- 
mals is  comparatively  small  under  ordinary  circumstances. 
The  amount  of  carbonic  anhydride  thus  eliminated  in  twenty- 
four  hours  in  man  is  estimated  at  not  more  than  10  grammes. 
It  varies  greatly,  however,  with  temperature,  exercise,  etc. 

The  skin  is  highly  vascular  in  mammals,  and  its  importance 
as  a  heat  regulator  is  thus  very  great. 

When  an  animal  is  varnished  over,  its  temperature  rapidly 
falls,  though  heat  production  is  in  excess.    From  the  fact  that 
life  may  be  prolonged  by  diminishing  loss  of  heat  through 
wrapping  up  the  animal  in  cotton-wool,  it  is  inferred  that 
depression  of  the  temperature  is,  at  all  events,  one  of  the  causes 
of  death.    Though  the  subjiect  is  obscure,  it  is  likely  that  th^ 
retention  of  poisonous  products  so  acts  as  to  derange  metabo-S 
lism,  as  well  as  poison  directly,  which  might  thus  lead  to  the? 
disorganisation  of  the  machinery  of  life  to  the  point  of  disrupt 
tion  or  death.    It  is  also  possible  that  the  reduction  of  the  tem- 
perature from  dilatation  of  the  cutaneous  vessels  may  be  so 
great  that  the  animal  is  cooled  below  that  point  at  wMch  the 
vital  functions  can  continue. 

Thb  Excrbtion  of  Pbrspibation. 

In  secretion  in  the  wider  sense  we  find  usually  certain  nerv- 
ous and  vascular  effects  associated.  The  vessels  supplying  the 
r.land  are  dilated  during  the  most  active  phase,  and  at  the  same 
i)ime  nervous  impulses  are  conveyed  to  the  secreting  cells  which 
stimulate  them  to  action.  There  is  a  certain  proportion  of 
water  given  off  by  traneiiiration;  but  the  sweat,  as  a  whole, 
even  the  major  part  of  the  water,  is  a  genuine  seoreticm,  the 
result  of  the  metabolism  of  the  cells. 

Certain  experimental  facts  deserve  consideration  in  this  con- 
nection :  1.  If,  in  the  oat,  the  sciatic  nerve  be  divided  and  its 
distal  end  stimulated,  even  when  the  vessels  of  the  leg  are  liga- 
tured, the  corresponding  foot  sweats.  %.  The  vessels  being  un- 
touched and  atropin  injected  into  the  blood,  no  sweating  occurs 
on  stimulation  of  the  nerve,  though  the  vessels  of  the  foot 


of  thecar- 
y  the  skin, 
ik  supplied 
hat  in  this 
artery  sup- 
most  mam- 
umstauces. 
in  twenty- 
)  grammes, 
se,  etc. 
importance 

ure  rapidly 
le  fact  that 
at  through 
ferred  that 
t  the  causes 
jly  that  th^ 
ige  metabo-S 
lead  to  the) 
it  of  disrupt 
of  the  tem- 
may  be  so 
t  -which,  the 


ertain  nery- 
ipplying  the 
at  the  same 
;  cells  which 
roportion  of 
as  a  whole, 
Ksrei^cm,  the 

I  in  this  oon> 
rided  and  its 
leg  are  liga- 
>ls  being  un- 
ating  occurs 
of  the  foot 


PROTECTIVE  AND  EXCRETORY  FUNCTIONS  OP  THE  SKIN.  417 

dilate.  3.  If  a  kitten  with  divided  sciatic,  and  as  a  consequence 
dilated  blood-vessels  in  the  corresponding  limb,  be  placed  in  a 
warm  oven,  the  other  feet  will  sweat,  while  the  one  the  nerves 
going  to  which  have  been  divided  remains  dry.  4.  Perspira- 
tion will  take  place  in  a  cat  that  has  just  died  under  the  cir- 
cumstances mentioned  in  1.  From  these  experiments  it  is 
clear  that  nervous  influences  alone,  in  the  absence  of  any  vas- 
cular changes,  or  in  the  total  deprivation  of  blood,  suffice  to 
induce  the  secretion  of  perspiration. 

If  the  central  stump  of  the  divided  sciatic  be  stimulated, 
sweating  of  the  other  Umbs  follows,  showing  that  perspiration 
may  bf  a  reflex  act.  It  is  found  that  stimulation  of  the  periph- 
eral end  of  the  divided  cervical  sympathetic  leads  to  sweating 
on  the  corresponding  side  of  the  face. 

Kvnui  Jhpkiogf. — Certain  nerves  (e.  g.,  the  cervical  sym- 
pathetic) have  been  stimulated  with  results  similar  to  those 
obtained  in  other  animals.  We  think  these  experiments  and 
certain  pathological  phenomena,  to  be  presently  mentioned,  of 
importance  beyond  their  immediate  application.  They  seem  to 
show  the  influence  of  nerves  over  vital  processes  in  the  clearest 
way,  and  render  it  probable- that  this  is  the  essential  element  in 
the  highest  vertebrates,  and  not  the  blood-supply,  which,  though 
important,  is  subsidiary.  The  path  of  the  sweat-nerves  is 
somewhat  similar  to  that  of  the  vaso-mator  fibers,  running 
mostly  i-a  the  sympathetic  in  some  part  of  their  course. 
Whether  there  is  a  dominant  center  in  the  medulla  and  subor- 
dinate ones  in  the  cord  is  a  matter  of  uncertainty ;  though,  that 
the  cerebrum  can  exercise  a  powerful  influence  over  the  sudor- 
ific glands  is  evident  from  the  effect  of  emotions. 

Certain  drugs  seem  to  act  on  the  centers  through  the  blood ; 
others  on  either  the  nerve  terminals  or  the  gland-cells  them- 
selves. It  is  true  that  some  of  these  will  induce  sweating  after 
the  nerves  have  been  divided,  though  conclusions  as  to  the  nor- 
tnal  action  of  a  part  from  such  experiments  must  be  drawn  with 
the  greatest  caution.  In  our  opinion  they  are  rather  suggest- 
ive than  demonstrative  in  themselves,  and  the  views  we  enter- 
tain of  normal  function  should  be  formed  from  h  consideration 
of  all  the  e^'^dence  rather  than  that  from  a  single  experiment, 
however  striking  in  itself. 

jjfWeating  during  dyspnoea  and  from  fear,  when  the  cutane- 
ous surfaces  are  pale,  as  well  as  in  the  moribund,  shows  also 
the  independent  influence  over  the  sudorific  glands  of  the  nerv- 
ous system.    Heat  induces  sweating  by  acting  both  reflexly  and 


II immummmmmim 


418 


ANIMAL  PHTSIOLOOT. 


directly  on  the  sweat-centers  we  may  suppose.  Unilateral 
sweating  is  known  as  a  pathological  as  well  as  experimental 
phenomenon.  Perspiration  may  be  either  increased  or  dimin- 
ished in  paralyzed  limbs,  according  to  circumstances.  It  is 
possible  that  there  is  a  paralytic  secretion  of  sweat  as  of  saliva. 
The  subject  is  very  intricate  and  will  be  referred  to  again  on 
aocoimt  of  the  light  it  throws  on  metabolic  processes  generally. 

Absorption  by  the  skin  in  man  and  other  mammals  is,  under 
natural  conditions  probably  very  slight,  as  would  be  expected 
when  it  is  borne  in  mind  that  the  true  skin  is  covered  by  sev- 
eral layers  of  cells,  the  outer  of  which  are  hardened. 

Ointments  may  unquestionably  be  forced  in  by  rubbing; 
and  perhaps  absorption  may  take  place  when  an  animal's  tis- 
sues are  starving,  and  food  can  not  be  made  available  through 
the  usual  channels.  ItisjCOTtain  that^braded  surfaces  are  aj 
source  of  danger,  from  affording^  means  of  entrance  for  < 

CO*  f orjgeinaK^ 

'stated  m  works  on 


Oompan^f*. — K  is  uisually  stated  m  works  on  physiology 
that  the  horse  sweats  profusely,  the  ox  less  so;  the  pig  in  the 
snout ;  and  the  dog,  cat,  rabbit,  rat,  and  mouse,  either  not  at  all 
or  in  the  feet  (between  the  toes)  only.  That  a  closer  observa- 
tion of  these  animals  will  convince  any  one  that  the  latter 
statements  are  incorrect,  we  have  no  doubt.  These  animals,  it 
is  true,  do  not  perspire  aenaMy  to  any  great  extent;  but  to 
maintain  that  their  akin  has  no  excretory  function  is  an  error. 

Wtmmuj. — ^The  skin  of  the  mammal  has  protective,  sensory, 
respiratory,  and  excretory  functions.  The  respiratory  are  in- 
significant under  ordinary  circumstances  in  this  group,  though 
well  marked  in  reptiles  and  especially  in  batraohians  (frog, 
menobranchus).  Sweating  is  probably  dependent  on  the  action 
of  centers  situated  in  the  brain  and  spinal  cord,  through  nerves 
that  run  generally  in  sympathetic  tracts  during  some  part  of 
their  course.  While  the  functicm  of  sweating  may  go  on  inde- 
pendently of  abundant  blood*supply>  it  ^is  usually  associated 
with  increased  vascularity. 

Sweat  contains  a  very  small  quantity  of  solids,  il  alkaline 
in  reaction  when  pure,  but  liable  to  be  acid  f  nnn  the  admixture 
of  sebaceous  matter  that  has  undergone  decomposition.  Sebum 
onsists  chiefly  of  olein,  palmitin,  soaps,  cholesterin,  and  ex- 
tractives of  little  known  composition.  The  salty  taste  of  the 
perspiration  is  due  chiefly  to  sodium  chloride,  and  its  smell  to 
volatile  fatty  acids ;  especially  is  this  so  of  the  sweat  of  certain 
parts  of  the  body  of  man  and  other  mammals. 


ilMIIMilUlMli 


mimmUiiimik 


Unilateral 
perimental 
L  or  dimin* 
aces.  It  ia 
18  of  saliTS. 
to  again  on 
s  generally, 
lis  is,  under 
be  expected 
red  by  sev- 

« 

»y  rubbing; 
mimal's  tis* 
ble  through^ 
rfaces  are  &. 

physiology 
le  pig  in  the 
ler  not  at  all 
Mer  observar 
it  the  latter 
le  animals,  it 
:tent;  but  to 
I  is  an  error, 
tive,  sensory, 
atory  are  in- 
roap,  though 
chians  (frog, 
on  the  action 
rough  nerves 
some  part  of 
y  go  on  inde> 
ily  associated 

Is,  i«  alkaline 
ihe  admixture 
ition.  Sebum 
erin,  and  ex- 
y  taste  of  the 
id  its  smell  to 
reat  of  certain 


1 


BXCBBTION  BT  THE  KIDNKT. 


419 


it<:viiMfdinr*mmii>iiNm 


The  functional  activity  of  the  skin  varies  with  the  tempera- 
ture, moisture,  etc.,  of  the  air  and  certain  internal  conditions; 
especially  is  it  important  to  remember  that  it  is  one  of  a  series 
of  excreioi'  organs  which  act  in  harmony  to  eliminate  the 
waste  OL  uhe  body,  so  that  when  one  functions  more  the  other 
may  and  usually  does  function  less. 

The  protective  function  of  the  skin  and  its  modified  epithe- 
lium (hair,  horns,  nails,  feathers,  etc)  is  in  man  slight,  but  very 
important  in  many  other  vertebrates,  among  which  provision 
against  undue  loss  of  temperature  is  one  of  the  most  constant- 
ly operative,  and  enables  a  vast  number  of  groups  of  animals 
to  adapt  successfully  to  their  varying  surroundings. 


EXCRETION  BY  THE  KIDNET. 

The  kidney  in  man  and  other  mammals  may  be  described  as 
a  very  complex  arrangement  of  tubes  lined  witii  many  different 
forms  of  secreting  cells,  sur- 
rounded by  a  great  mesh- 
work  of  capillaries^  bound 
together  by  connective  tis- 
sue, tho  quantity  varying 
wifli  the  animal,  and  the 
whole  inclosed  in  a  capsula 
The  organ  is  well  supplied 
with  lymphatics  and  nerves. 
Though  the  tubes  are  so 
complex,  the  kidney  may  be 
divided  into  SEOnes  which 
contain  mostly  but  one  kind 
of  tubule. 

Oomparttifs.— Among  the 
lowest  forms,  the  Infuaori- 
ana  and  Coeienteraies,  ex- 
cretory organs  have  not 
been  definitely  traced.  In 
the  Vermes,  organs  known 
as  nephridia  (segmental  or- 
gans, see  Figs.  358, 357)  are 
supposed  to  act  the  part  of 
the  kidney  in  some  fashion. 
These  ara  long,  often  ooUed 


430 


ANIMAL  PHYSIOLOGY. 


ttibes  lined  with  cells,  and  with  an  internal,  cilated,  ftumel- 
shaped  extremity  opening  into  the  body  cavity.    In  such  cnw- 


nwUc).    A.  OivlBMiwo(jortteia  ij^rtMCfc    B.  "" 


.  body:«- 
;  I,J;aw. 
ooBUBimi- 


tubw.  Sa.  BMlioBofaMighttube. 


»jt««tilftaBi»afeiteitraiiii!'aiiiiiii«*^'w«'--' 


sd,  ftumel- 
such  cms- 


EXCSBTION  BY  THE  KIDNEY. 


4S1 


lollMT  I 

manrtMe;  S,nw 


taceans  as  tho  crayfish  the  green  gland  is  supposed  to  repre- 
sent a  kidney.  It  does  not  open  into  the  body  cavity  like  the 
preceding  and  the  following  form  of  the  organ.  It  is  well  sup- 
plied with  capillaries.    The  organ  of  Bojanus  (Fig.  306)  is  the 


<Rilw"i']iiihr)Biii»i>tiiMi'i* 


Fia.  an.-Blood^vMMli  of  MUpiBlalu  bodtaa  and  oomotaiwd  *>iili>»S*JiiS!S^i!lSSS!'S£i, 

main  excretory  channel  in  many  groups  of  moUusks.  In  in- 
sects the  long,  coiled  Malpighian  tubules,  which  open  into  the 
intestine,  are  believed  to  secrete  both  bile  and  uric  acid. 

Among  vertebrates,  till  the  reptiles  are  reached,  the  kidney 
is  a  persistent  Wolffian  body,  hence  its  more  simple  form. 


._J 


iv 


ANIMAL  PHYSIOLOGY. 

In  most  fishes  the  kidney  i» 
a  very  elongated  organ,  though 
in  the  lowest  it  consists  of  little 
more  than  tubules,  coiling  but 
►0  slightly,  ending  by  one  extrem- 
ity in  a  glomerulus  and  by  the 
other  opening  into  a  long  com- 
mon efferent  tube  or  duct.  The 
glomerulus  is,  however,  pecul- 
iar to   the  vertebtite  kidney. 
The  graded  complexity  in  ar- 
rangement, etc.,  of  the  tubes  is 
*B  represented  well  in  the  figure 
below.    It  is  a  significant  fact 
that  the  kidney  of  the  human 
subject  is  lobulated  in  the  em- 
bryo, which  condition  is  persist- 
ent in  some  mammals  (rumi- 
nants, etc.). 

(Ab  the  lungs  are  the  organs 
employed  especially  for  the 
elimination  of  carbonic  anhy- 
dride, so  the  kidneys  are  above 
all  others  the  exoretors  of  the 
nitrogenous  waste  products  of 
the  body  chiefly  in  the  form  of 
uric  acid  or  urea.  Before  treat- 
ing of  secretion  by  the  kidney 
it  will  be  well  to  examine  into  the  physical  and  chemical  prop- 
erties  of  urine  with  some  detail,  especially  on  account  of  its 
great  impor^nce  in  the  diagnosis  of  disease. 

UbINK  CONSIDKBLi)  PHYSICALLY  AND  OHBMICALLY. 

Urine  is  naturally  a  fluid  of  very  variable  composition,  espe- 
cially regarded  Quantitatively-*  fact  to  be  borne  m  Mnd  m 
considering  all  statements  of  the  constitution  of  this  fluid. 

BdmUo  flxatitj.— Urine  must  needs  be  heavier  than  water,  on 
account  of  the  large  variety  of  solids  it  contains.  The  average 
specific  gravity  of  the  urine  for  the  twenty-f our  hours  is  1016 
to  loao.  It  is  lowest  in  the  morning  and  varies  greatly  witn 
the  quantity  and  kind  of  food  eaten,  the  activity  of  the  lungs 
and  especially  of  the  skin,  with  emotions,  etc. 


dMribaUon  of  tubulM  at  k>dMT(< 
Hnxlesr).  C,  corttoal  i«Khm ;  0,  b« 
ttj KNie, conUiniiut targe  P«* o^rrT. 

•M  the  main  outsDW  tunulaa. 


IBSiMMl 


EXCBBTION  BY  THK  KIDNEY. 


428 


kidney  it 
a,  though 
Is  of  little 
filing  but 
ke  extrem- 
,nd  by  the 
long  com- 
iuct.  The 
rer,  pecul- 
»  kidney, 
ity  in  ar- 
te tubes  is 
the  figure 
ficant  fact 
he  human 
in  the  em- 
L  is  persist- 
als  (rumi- 

the  organs 
f  for  the 
onic  anhy- 
1  are  above 
tors  of  the 
)roducts  of 
he  form  of 
ef ore  treat- 
the  kidney 
mical  prop- 
K>unt  of  its 


CALLT. 

mtion^espe- 
in  inind  in 
Isflmd. 
an  water,  on 
rhe  average 
ours  is  1015 
ipreatly  with 
)f  the  lungs 


dolor.— A  light  straw  color,  which  is  also  very  variable, 
being  increased  in  depth  either  by  the  presence  of  an  excess  of 
pigment  or  a  diminution  of  water.  There  are  probably  several 
pigments,  among  which  occur  urcbUin,  derived  probably  from 
bile  pigment;  urochrome,  becoming  red  on  oxidation;  and 
indican,  which  may  be  oxidized  to  indigo. 

This  XMMtlon  of  human  urine  is  acid,  owini;  to  acid  salts,  espe- 
cially acid  sodium  phosphate  (NaH,P04).  There  is  usually  but 
a  trifling  qvantity,  if  any,  of  free  acid  in  the  urine  when 
secreted.  The  acidity  diminishes  after  meals,  and  the  urine 
may  be  neutral  or  alkaline  when  the  food  is  wholly  vegetable, 
or  unduly  acid  when  the  diet  is  entirely  fleshy. 

Qniatlty.— Usually  about  1,500  c.c.  or  from  50  to  52  ounces 
(two  pints)  in  twenty-four  hours.  This  is,  of  course,  like  the 
specific  gravity,  highly  variable,  and  frequently  they  run  par- 
allel with  each  other. 

The  following  tabular  statement  Will  prove  useful  for  refer- 
ence: 

QuarUUative  Estimation  of  the  CwuiUuenis  of  the  Urine  for 
Tiventy-four  flows  {after  Parkes). 


Wa,tm 

Tota^  BolidB. . . 

Utw 

Uricaoid 

Hippario  aoid. 
Creatfnin 


Pigment,  etc. 
Siuphi 


man  of  66  Una. 


Ipharie  acid  . 
Ph(M|riiorio  aoid. 

ClilonDe 

Ammonia 

PotaMium * 

Sodium 

Galoium 

Magnesium 


FwiklloM 
body  weight. 


28-000 
11000 
•5000 
-0064 
•0000 
•0140 
•1510 
•0806 
•OffiO 
•IMO 


Attention  is  directed  more  particularly  to  the  preponderance 
among  the  solids  of  urea,  and  sodium  chloride,  for  the  latter  is 
the  form  in  which  a  large  part  of  the  sodium  reappears.  We 
may  say  that  in  round  niunbers  about  35  grammes  or  600  grains 
(2  to  3  per  vent)  of  urea  are  excreted  daily. 

VitnfmoBt  OryitaUiM  ledlM.— These  are  the  dezivatives  of 
the  metabolism  of  the  body,  and  not  in  any  appreciable  degree 
drawn  from  the  food  itself.    Besides  urea,  and  of  much  less 


MM! 


4U 


ANIMAL  PHTSIOLOOT. 


importance,  occarring  in  small  quantities,  are  bodies  that  may 
be  regarded  as  less  oxidized  forms  of  nitrogenous  metabolism, 
such  as  creatinin,  xanthin,  hypoxauthin  (sarkin),  hippuric  acid, 

ammonium  oxalurate,  and  urea,  C/O^t^g*.    The  latter  was 

first  prepared  artificially  from  ammonium  cyanate,  ^^  >  O, 

with  which  it  is  isomeric. 

When  air  has  free  access  to  urine  for  some  time  in  a  warm 
room,  the  urea  becomes  ammonium  carbonate  by  hydration, 
probably  owing  to  the  influence  of  micro-organisms,  thus: 
CO  (NH»)i  +  2  H,0  s  (SUt),  COt;  hence  the  strong  ammonioal 
smell  of  old  urine,  urinals,  etc. 

Uric  acid  (CiH4N4(\)  occurs  sparingly  (see  table),  combined 
with  sodium  and  ammonium  chiefly  as  acid  salt&  Since  these 
salts  are  not  so  soluble  in  cold  as  in  warm  water,  they  often 
fall  as  a  sediment  in  the  vessel  in  which  the  urine  stands,  and 
present  a  brick-red  or  fawn  color. 

Uric  acid  is  itself  rather  insoluble  in  cold  water  or  hydro- 
chloric acid,  though  soluble  in  alkalies;  hence  it  may  be 
obtained  by  adding  hydrochloric  acid  to  the  urine  in  the  cold. 
When  it  is  in  excess  it  may  separate  out  on  standing,  forming 
characteristic  cdorcd  (dark-red)  crystals,  adhering  to  the  sides 
of  the  vessel,  floating  on  the  top  of  the  urine,  or  as  a  sediment 
at  the  bottom  (like  red-pepper  grains). 

V4»<«ttrogiB0U  OigaiilD  Bo4iM.— Whether  traces  of  sugar  are 
normal  in  urine  is  as  yet  undetermined.  Certain  acids  occur, 
at  least  frequently,  in  small  quantities,  and  combined  mostly 
with  bases.  Among  these  are  lactic,  formic,  oxalic,  succinic, 
etc.  A  series  of  well-known  aromatic  bodies  occurs  in  urine, 
especially  in  that  of  the  horse,  cow,  etc.  These  are  phenol, 
oresol,  pyrocatechin,  which  occur  not  free,  but  united  with  std- 
phurio  acid.  \. 

IiungaaiA  lattn — These  are  mostly  in  simple  solution^  in  urine, 
and  not,  as  in  some  other  fluids  of  the-  body,  united  with  pro- 
teid  bodies.  The  salts  are  chlorides,  phosphates,  sulphates, 
nitrates,  and  carbonates,  the  first  three  being  the  most  Abun- 
dant; the  bases  being  sodium,  potassium,  calcium,  magnesium. 
Since  the  earthy  salts  can  not  remain  in  solution  in  an  alkaline 
fluid,  they  are  usually  found  as  a  sediment  when  the  urine  loses 
its  acid  reaction.  The  phosphates  are  to  be  traced  to  the  food, 
to  the  phosphorus  of  proteids,  $nd  to  phosphorized  fats  (leci- 
thin). The  sulphates  are  derived  from  those  of  the  food  and 
from  the  sulphur  of  the  proteids  of  the  body.    So  much  of  the 


liilwwiiiii       tniiiiri 


I  that  may 
etabolism, 
puric  aoid, 

latter  was 


in  a  warm 
hydration, 
sms,  thus: 
Etmmonical 

,  combined 
Since  these 
they  often 
itands,  and 

'  or  hydro- 
it  may  be 
in  the  cold, 
[g,  forming 
bo  the  sides 
a  sediment 

f  sugar  are 
kcids  occur, 
aed  mostly 
c,  succinic, 
■s  in  urine, 
ure  phenol, 
d  with  sul* 

>n^  in  urine, 
d  with  pro- 
sulphates, 
most  Abun- 
nagnesium. 
an  alkaline 
urine  loses 
to  the  food, 
I  fats  (leci- 
e  food  and 
luch  of  the 


EXCRETION  BT  THE  KIDNEY. 


498 


carbonates  as  is  not  derived  directly  from  a  corresponding  sup- 
ply in  the  food  may  be  traced  to  the  oxidation  of  certain  or- 
ganic salts,  as  citrates,  tartrates,  etc. 

Doubtless  mapy  bodies  appear  either  regularly  or  occasion- 
ally in  urine  that  have  so  far  escaped  detection,  which  are,  like 
the  poisonous  exhalations  of  the  lungs,  not  the  less  important 
because  unknown  to  science. 

Abnflimuil  Vrint. — ^There  is  not  a  substance  in  the  urine  that 
does  not  vary  under  disease,  while  the  possible  additions  act- 
ually known  are  legion.  These  may  be  derived  either  from 
the  blood  or  from  the  kidneys  and  other  jMtrts  of  the  urinary 
tract.  The  kidneys  seem  to  take  upon  themselves  more  readily 
than  any  other  organ  the  duty  of  eliminating  foreign  matters 
from  the  body.  But  this  aspect  of  the  subject  is  too  wide  for 
detailed  consideration  in  this  work. 

The  student  of  medicine  should  be  thoroughly  familiar  with 
the  urine  in  its  normal  condition  before  he  enters  upon  the 
examination  of  the  variations  produced  by  disease.  This  is 
not  difficult,  and  much  of  it  may  be  carried  out  with  but  a 
meager  supply  of  apparatus.  For  this  purpose,-  however,  we 
recommend  some  work  devoted  to  the  chemical  and  micro- 
scopic study  of  the  urine. 

It  greatly  assists  to  remember  a  few  points  in  regard  to 
solubilities.  From  a  physiologici^  point  of  view,  the  urine  and 
its  variations,  as  the  result  of  changes  in  the  organism,  may  be 
observed  with  advantage  in  one's  own  person— e.  g.,  the  influ- 
ence of  food  and  drink,  temperature,  emotions,  etc. 

Oompantlt*.— The  urine  of  most  vertebrates  is  of  higher  spe- 
cific gravity  than  that  of  man.  In  fishes,  reptiles,  and  birds, 
uric  acid  replaces  urea,  and  is  very  abnndaht.  In  these  animals 
most  of  this  substance  is  white.  The  urine  is  passed  with  the 
f seces.  Among  mammals  the  urine  of  the  camivora  is  strongly 
acid,  perhaps  owing  in  great  part  to  the  flesh  on  which  they 
feed;  and  abounds  in  phosphates  and,  in  some  instances,  sul- 
phates. The  urine  is  sq  concentrated  in  some  cases  that  we 
have  known  urea  nitrate  to  cryktalliae  out  on  the  addition  of 
nitric  acid  without  requiring  condensation. 

The  urine  of  the  herbivora  is  alkaline,  and  abounds  in  salts 
of  calcium,  especially  carbonates.  It  is  also  of  high  sjiecific 
gravity,  and  grows  rapidly  dark  in  color  when  passed,  owing 
probably  tu  the  presence  of  the  aromatic  compounds  referred 
to  above,  derived  from  the  food.  In  certain  groups  of  inverte- 
brates uric  acid  seems  to  be  a  normal  excretion. 


[^Mteiitt^MnMriMtaiM 


•aoH 


4M 


ANIMAL  PHTSIOLOOY. 


The  Skcbbtion  of  Ubink. 

Among  experimental  facts  from  which  important  conclu- 
sions have  been  drawn  are  the  following  (whto  blood-pressure 
within  the  kidney  is  referred  to,  it  will  be  understood  that  the 
glomeruli  are  meant):  1.  Section  of  the  spinal  cord,  which 
greatly  lowers  the  general  blood-pressure,  is  followed  by  dimi- 
nution or  total  arrest  of  the  secretion  of  urine.  2.  Section  of 
the  renal  nerves,  and  to  a  less  extent  of  the  splanchnics  de- 
creases the  flow  of  urine.  3.  Stimulation  of  the  spinal  cord 
after  section  of  the  above  nerves  (which  raises  the  blood-press- 
ure in  the  kidney  by  elevating  the  general  blood-pressure)  in- 
creases the  flow  of  urine.  4.  Certain  diuretics  increase  the 
blood-pressure,  either  generally  or  in  the  kidney,  while  others 
act  on  the  renal  epithelium,  apparently  independently  of  blood- 
pressure. 

By  means  of  apparatus  adapted  to  register  the  changes  of 
volume  the  kidney  undergoes,  it  is  found  that  the  kidney  not 
only  responds  to  every  general  change  in  blood-pressure,  but 


Tta. 


kIdMj ;  T,  tlni»ciirT«, 


to  each  heart-beat— that  is,  its  volume  varies  momentarily. 
This  shows  how  sensitive  it  is  to  variations  in  blood-pressure. 

From  the  above  and  other  experiments  it  has  been  concluded 
that  the  secretion  of  urine  is  largely  dependent  on  blood-press- 
ure. Until  very  recently  certain  experiments  (of  NusslMium) 
were  considered  as  favoring  the  view  that  the  activity  of  the 
glomeruli  was  of  a  wholly  or  greatly  different  character  from 
that  of  the  tubules.  In  the  amphibia  (frog,  newt,  etc.)  there  is 
a  double  renal  blood-supply.  The  glomeruli  derive  their  blood 
from  the  renal  artery,  and  the  tubules  from  the  renal-portal 
system.  The  vein  returning  the  blood  from  the  lower  extrem- 
ity divides  (Fig.  331)  at  the  upper  part  of  the  thigh  into  two 
branches,  one  of  which,  entering  tiie  kidney,  breaks  up  into 


BXCRBTION  BY  THE  KIDNBT. 


4t7 


it  conolti- 
l-pressure 
1  that  the 
>rd,  which 
I  by  dimi- 
Section  of 
chnics  de* 
;>iiial  cord 
lood-press- 
essure)  in- 
sreaae  the 
bile  others 
f  of  blood- 
changes  of 
kidney  not 
Bssure,  but 


Bnjr). 


»mentarily. 
pressure. 
I  concluded 
ilood-press- 
IS'ussbaum) 
vity  of  the 
actor  from 
be.)  there  is 
their  blood 
■enal-portal 
rer  extrem- 
h  into  two 
,ks  up  into 


oapillaries  around  the  tubules,  which  inosculate  to  some  extent 
with  the  veseels  emerging  from  the  glomeruli  It  was  found 
that  when  certain  substences  were  injected  into  the  blood  they 
no  longer  appeared  in  the  urine  after  the  renal  artery  had  been 
tied,  from  which  it  was  concluded  that  they  were  secreted  only 
by  the  glomeruli,  and  that  the  blood  of  the  renal-portal  vein 
did  not  find  access  to  the  glomeruli  This  conclusion  was  a 
pretty  bold  leap,  but  there  was  some  show  of  reason  for  it. 
More  recently,  however,  these  experimente  have  been  demon- 
strated to  be,  to  a  certain  extent,  unreliable,  and  that  the  pas- 
sage of  blood  from  the  venous  capillaries  backward  can  really 
take  place,  to  some  extent,  after  a  time. 

Theories  legarding  the  secretion  of  urine  may  be  divided 
into  those  that  are  almost  wholly  mechanical,  partly  mechani- 
cal, and  purely  secretory:  1.  To  the  first  class  belongs  that  of 
Ludwig,  which  teaches  that  very  diluto  urine  is  separated  from 
the  blood  in  the  glomeruli,  and  by  a  process  of  endosmosis  and 
absorption  of  water  by  the  tubular  capillaries  is  gradually 
concentrated  to  the  normal.  2.  As  an  example  of  the  second 
class  is  that  of  Bowman,  who  maintained  that  the  greater  part 
of  the  water  and  some  of  the  more  soluble  and  diffusible  salte  are 
separated  by  the  glomeruli  but  the  characteristic  constituente 
of  the  urine  by  the  epithelium  of  the  renal  tubules.  8.  As  an  ex^ 
ample  of  the  third  is  the  theory  of  Heidenhain,  who  attributed 
little  to  blood-pressure  in  itself,  and  much,  if  not  the  whole,  to 
the  secreting  activity  of  the  epithelium  of  the  tubules  more  par- 
ticularly. This  physiologist  showed  that  while  ligature  of  a 
vein  raised  the  blood-pressure  within  a  glomerulus,  it  was  not 
followed  by  any  increase  in  the  quantity  of  the  secretion,  but 
by  ite  actual  arrest  He  also  showed  that  injection  of  a  colored 
substance  (sodium  sulphindigodate)  into  the  blood,  after  the 
pressure  had  been  greatly  lowered  by  section  of  the  spintd 
cord,  led  to  ite  appearance  in  the  urine ;  and  microscopic  exam- 
ination showed  that  it  had  passed  through  the  epithelial  cells 
of  the  tubules,  not  of  the  glomeruli 

It  is  found,  however,  that  after  the  removal  of  a  ligature 
applied  to  the  renal  artery  the  urine  is  albuminous,  showing 
that  the  cells  have  been  plainly  injured  by  the  operation ;  hence 
Heidenhain's  experiment  described  above  is  not  valid  against 
the  blood-pressure  theory.  Moreover,  too  much  must  not  be 
inferred  from  the  action  of  foreign  substances  under  the  ab- 
normal conditions  of  such  an  experiment,  t  While  some  physi- 
ologists claim  that  the  glomeruli  are  filtering  mechanisms,  they 


4S8 


ANIMAL  PHTSIOLOOr. 


|\. 


explain  that  filtration  is  not  to  be  und^ir  i -ju  Iii  itS  ordinary 
laboratory  acceptation,  but  that  the  glonu  .;'  ''>.c:riminate  as 
to  what  they  allow  to  pam,  yet  they  in  )  ray  explain  how 
this  is  done.  They  make  the  whole  process  depend  ou  blood- 
pressnre,  and  attribute  little  special  action  to  the  flat  epithe- 
lium of  the  Malpighian  capsules. 

Though  we  can  not  admit  the  full  force  of  Heidenhain's  ex- 
periments as  he  interprets  them,  we  still  believe  that  his  views 
are  most  in  harmony  with  the  general  laws  of  biology  and  the 
special  facts  of  renal  secretion.  Recently,  after  a  repetition  of 
Nussbaum's  experiments,  and  the  institution  of  others,  it  has 
been  rendered  clear  that  the  mechanical  theory  of  the  work  of 
the  kidney  can  not  hold,  even  of  the  glomeruli,  which  are 
shown  to  be,  as  we  should  have  expected,  true  secreting  organs. 
Now,  there  can  be  no  doubt  that  blood-pressure  is  a  most  im- 
portant determining  condition  here  as  in  other  secreting  pro- 
cesses, in  the  mammal  at  all  events ;  but  whether  of  itself  or 
because  of  the  influence  it  has  on  the  rapidity  of  blood-flow,  it 
is  difficult  to  determine ;  or  rather  whether  solely  to  the  latter, 
for  that  the  constant  supply  of  fresh  blood  is  a  regular  con- 
dition of  normal  secretion  there  can  be  no  doubt.  Further,  it 
seems  probable  that  blood-pressure  has  more  to  do  with  the 
secretion  of  water  than  any  other  constituent  of  urine.  But 
we  maintain  that  it  shotild  be  called  a  genuine  secretion,  and 
that  nothing  is  gained  by  using  the  term  *' filtration  "—on  the 
contrary,  that  it  is  misleading,  and  tends  to  divert  attention 
from  the  real  though  often  hidden  nature  of  vital  processes. 
The  facts  of  disease  and  the  evidence  of  therapeutics,  we  think, 
all  favor  such  a  view  of  the  work  of  the  kidneys. 

(iTerves  having  an  influence  over  the  secretion  of  urine  simi- 
lar to  those  acting  on  the  digestive  glands  have  not  yet  been 
determined.  The  powerful  influence  of  emotion,  especially  in 
those  of  unstable  nervous  system,  over  the  secretion  of  urine 
shows  that  there  must  be  nervous  channels  tiirough  which  the 
nerve-centers  act  on  the  kidneys ;  though  whether  the  results 
are  not  wholly  dependent  upon  vaso-motor  effects  may' be  con- 
sidered as  an  open  question  by  many.  We  think  such  a  view 
improbable  in  the  highest  degree.  The  most  recent  investiga- 
tions would  seem  to  show  that  the  vaso-motor  fibers  run  in  the 
dorsal  nerves,  especially  the  eleventh,  twelfth,  and  thirteenth, 
and  that  cc  these  the  vaso-constrictors  are  the  hesL  developed. 

PttihskgioaL — ^When  the  kidneys  are  excised,  the  ureters 
ligatured,  or  when  the  former  are  so  diseased  as  to  be  inca- 


MM 


EXCRETION  BY  THE  KIDNEY. 


499 


B  ordinary 
iminate  as 
plain  how 
on  blood- 
lat  epithe- 

ihain's  ex- 
;  his  views 
ly  and  the 
petition  of 
lers,  it  has 
lie  work  of 
which  are 
ng  organs. 
k  most  im- 
reting  pro- 
>f  itself  or 
[)od-flow,  it 
I  the  latter, 
tgnlar  con- 
Further,  it 
[o  with  the 
irine.    But 
iretion,  and 
a"— on  the 
t  attention 
[  processes. 
},  we  think, 

urine  simi- 
)t  yet  been 
specially  in 
m  of  urine 
L  which  the 
the  results 
aay'be  con- 
luch  a  view 
k  investiga- 
1  run  in  the 
thirteenth, 
leveloped. 
the  xireters 
to  be  inca- 


pable of  performing  their  functions,  death  is  the  result,  being 
preceded  by  marked  depression  of  the  brain-centers  passing 
into  coma.     Elxactly  which  of  the  retained  products  brings 
about  these  results  is  not  known.    They  are  likely  due  to  sev- 
eral, and  it  impresses  on  the  mind  the  importance  of  those 
processes  by  which  the  constantly  accumulating  waste  is  elimi- 
nated.  Uric  acid  when  not  removed  from  the  blood  and  tissues 
is  supposed  to  be  the  exciting  cause  of  gout.    An  excess  in  the  ) 
f5rm  of  urates  retained  or  deposited  in  certain  parts,  especially  ( 
the  joints,  is  frequently  at  all  events  an  accompaniment  of  this  ) 
disease. 

Thk  Expulsion  or  Urine. 

We  now  present  in  concise  form  certain  facts  on  which  to 
base  opinions  as  to  the  nature  of  the  processes  by  which  the 
bladder  is  emptied. 

It  will  be  borne  in  mind  that  the  secretion  of  urine  is  con- 
stant, though  of  course  very  variable;  that  the  urine  is  con- 
veyed in  minute  quantities  by  rhythmically  contractile  tubes 
(ureters)  which  open  into  the  bladder  obliquely  ;•  and  that  the 
bladder  itself  is  highly  muscular,  the  cells  being  arranged  both 
circularly  and  obliquely,  with  a  special  accumulation  of  the 
circular  fibers  around  the  neck  of  the  organ  to  form  the  sphinc- 
ter vesica. 

1.  It  is  found  that  the  pressure  which  the  sphincter  of  the 
bladder  can  withstand  in  the  dead  is  much  less  (about  one 
third)  than  in  the  living  subject.  2.  We  are  conscious  of  being 
able  to  empty  the  bladder,  whether  it  contains  much  or  little 
fluid.  3.  We  are  equally  conscious  of  an  urgency  to  evacuation 
of  the  vesical  contents,  according  to  the  fullness  of  the  organ, 
the  quality  of  the  urine,  and  a  variety  of  other  conditions. 

4.  Emotions  may  either  retard  or  render  micturition  urgent. 

5.  In  a  dog,  in  which  the  cord  has  been  divided  in  the  dorsal 
region  some  months  previously,  micturition  may  be  induced 
reflexly,  as  by  sponging  the  anus.  6.  In  the  paralyzed  there 
may  be  retention  or  dribbling  of  urine.  7.  In  cases  of  urethral 
obstruction  from  a  calculus,  stricture,  etc.-,  there  may  be  excess- 
ive activity  of  the  muscular  tissue  of  the  bladder-walls.  8. 
Evacuation  of  the  bladder  may  occur  in  the  absence  of  con- 
sciousness (sleep). 

The  most  obvious  conclusions  from  these  facts  are  that-^1. 
The  urine  finds  its  way  to  the  bladder  partly  through  muscular 
(peristaltic)  contractions  of  the  ureters,  partly  through  gravity, 


480 


ANIMAL  PHYSIOLOGY. 


\ 


in  man  at  all  events,  and  partly  from  tlie  pressure  within  the 
tubules  of  the  kidneys  themselves.  2.  The  evacuation  of  urine 
may  take  place  independently  of  the  will  (see  8),  and  is  a  reflex 
(5)  act.  3.  Micturition  may  be  initiated  by  the  will,  which  is 
usually  the  case,  when  by  the  action  of  the  abdominal  muscles 
a  little  urine  is  squeezed  into  the  urethra,  upon  which  afferent 
impulses  set  up  contractions  of  the  bladder  by  acting  on  the 
detrusor  center  of  the  cord  and  at  the  same  time  inhibit  the 
center  presiding  over  the  sphincter  (if  such  there  be),  permit- 
ting of  its  relaxation.  4.  Emotions  seem  to  interfere  with  the 
ordinary  control  of  the  brain-centers  over  those  in  the  spinal 
cord.  S.  It  may  be  assumed  that  the  normal  tone  of  the 
sphincter  of  the  bladder  is  maintained  reflexly  by  the  spinal 
cord.  The  unwonted  muscular  contraction  associated  with  an 
obstruction  to  the  outflow  of  urine  may  be  in  part  of  nervous 
origin,  but  is  also,  in  all  probability,  owing  in  some  degree  to 
the  muscle-cells  resuming  an  independent  contrac^lity,  due  to 
what  we  recogniafe  as  the  principle  of  reversion.  The  same  is 
seen  in  the  heart,  ureters,  and  similar  structures. 

Fafhokgiml. — ^There  may  be  incontinence  of  urine  from  pa- 
ralysis, the  cerebral  ccr.tbxtt  being  unable  to  control  those  in 
the  spinal  cord.  Dribbling  of  urine  may  be  due  to  retention  in 
the  first  instance,  the  tone  of  the  sphincter  being  finally  over- 
come, owing  to  increase  of  pressure  within  the  bladder.  Over- 
distention  of  the  bladder  may  arise  in.  consequence  of  lack  of 
tone  in  the  muscular  walls,  though  this  is  rare.  Strangury  is 
due  to  excessive  aoticm  of  the  walls  of  the  bladder  and  the 
sphincter,  brought  about  reflexly,  when  the  organ  is  unduly 
irritable,  as  in  inflammation,  after  the  abuse  of  certain  drugs 
(cantharides),  etc. 

Oaaptntit*. — In  man  the  last  drops  of  urine  are  expelled  by 
the  action  of  the  bulbo-oavemosus  muscle  and  perhaps  some 
others.  In  the  dog  and  many  other  animals  the  regulated  and 
voluntary  use  of  this  muscle,  marked  in  a  high  degree^  produces 
that  interrupted  flow  so  characteristic  of  the  micturition  of 
these  animals. 

IttUMtfy.-— Urine  is  in  man  a  fluid  of  speoiflc  gravity  1010 
to  1020,  acid  in  reaction,  pale  yellow  in  color,  and  containing 
certain  saltu,  pigments,  and  nitrogenous  bodies.  The  chief  of 
the  latter  is  urea,  which  is  excreted  daily  to  the  extent  of  about 
one  ounce  (800  grains). 

The  kidneys  and  skin  especially  supplement  one  anothe^ 
fmd  normally  great  activity  of  the  one  implies  lessened  acfj 


IMillUMMi 


MMMMMIil 


vithin  the 
a.  of  urine 
is  a  reflex 

which  is 

muscles 

h  afferent 

ag  on  the 

ihibit  the 

),  permit- 
e  with  the 
the  spinal 
ne  of  the 
the  spinal 
d  with  an 
>f  nervous 
)  degree  to 
ity,  due  to 
be  same  is 

i  from  pa- 
il those  in 
atention  in 
nally  over- 
ler.  Over- 
of  lack  of 
'rangury  is 
ar  and  the 
is  unduly 
tain  drugs 

)xpelled  by 
haps  some 
ulated  and 
e^  produces 
tnrition  of 

ravity  lOlS 
containiug 
he  chief  of 
at  of  about 

le  anotheM 
MBsened  ac^ 


THE  METABOLISM  OF  THE  BODT.  481 

tivity  of  the  other.    This  is  availed  of  in  the  treatment  of  dis- 


Both  the  Malpighian  capsules  and  the  renal  tubules  have  a 
true  secretory  function,  though  the  larger  part  of  the  water  of 
urine  is  secreted  by  the  former.  Blood-pressure  is  an  important 
condition  of  E.ecretion,  though  it  is  likely  that  this  is  so  chiefly 
because  it  favors  a  rapid  renewal  of  the  blood  circulating 
through  the  organ.  Whether  there  are  nerves  that  influence^ 
secretion  directly,  as  in  the  case  of  the  skin,  is  not  determined/ 
/Suppression  of  the  renal  functions  leads  to  symptoms  in 
wMch  the  nervous  system  is  recognized  as  suffering  to  the 
extent  ofteiLfif  coma,  ending  in  dejath.  The  urine  of  most  other 
animals  is  more  concentrated  than  that  of  man ;  this  secretion 
in  carnivora  being  acid,  and  in  herluvora  alkaline  in  reaction 
when  passed  a  short  time. 

Out*  iuformatioi-  in  regard  to  the  kidneys  has  been  derived 
experimentally  chiefly  from  the  study  of  the  frog  and  a  few  of 
the  domesticated  mammals,  especiallv  the  dog ;  and  as  regards 
some  points  of  interest,  so  far  as  imne  is  concerned,  from,  the 
bird  (guano),  and  the  horse,  ox  (aromatic  compounds),  etc. 
Man's  urine  has  been  thoroughly  studied ;  but  the  nature  of  > 
the  act  of  renel  secretion  is  in  his  case  a  matter  of  inference] 
from  the  facts  of  pathology,  clinical  medicine,  therapeutics,  etc. ) 


THE  METABOLIBM  OF  THE  BODT. 

In  the  widest  sense  the  term  metaboliem  may  be  conven- 
iently applied  to  all  the  numerous  changes  of  a  chemical  kind, 
resulting  from  the  activity  of  the  protoplasm  of  any  tissue  or 
organ.    In  a  more  restricted  meaning  it  is  confined  to  changes 
tmdergone  by  the  food  from  the  time  it  enters  till  it  leaves  the 
body,  iu.  so  far  as  these  are  not  the  result  of  obvious  mechani- 
cal causes.    The  sense  in  which  it  is  employed  in  the  present 
chapter  will  be  plain  from  the  context,  though  usually  we  shall 
be  concerned  with  those  changes  effected  in  the  as  yet  compara- 
tively unprepared  products  of  digestion,  by  which  they  are  ele-  ' 
vated  to  a  higher  rank  and  brought  some  siepa  nearer  to  the 
final  goal  toward  which  they  have  been  tending  from  the  first. 
As  yet  our  attempts  to  trace  out  these  steps  Lave  been  little"^ 
better  than  the  fruitless  efforts  of  a  lost  traveler  u>  find  a  road,) 
the  general  direction  of  which  he  knows,  but  the  ways  by  which  j 
it  is  reached  only  the  subject  of  plausible  conjecture.    But/ 


mmt 


482 


ANIMAL  PHYSIOLOOT. 


any  theories  that,  like  a  scaffolding,  allow  of  or  help  to  addi- 
tional investigation,  and  in  any  way  lead  out  into  a  clearer 
light,  are  not  without  value ;  and  on  this  principle  we  shall 
treat  the  subject,  spending  but  little  time  in  barren  fields 
except  as  they  have  an  interest  from  the  suggestiveness  of  the 
results,  even  though  negative. 


^ 


The  Metabolism  ov  the  Liybb. 

This  organ  has  two  well-recognized  functions :  1.  The  for- 
mation of  bile.    2.  The  formation  of  glycogen. 

We  have  already  considered  the  first,  and  ascertained  how 
little  is  positively  known.    Let  us  now  examine  the  second. 

Glycogen  may  be  obtained  from  the  liver  of  mammals,  such 
as  the  rabbit,  by  rapidly  killing  the  animal,  excising  the  warm 
still  living  organ,  cutting  into  fine  pieces,  throwing  them  into 
boiling  water,  removing  after  a  few  minutes  and  grinding  in  a 
mortar  and  reimmersing  in  the  boiling  water ;  on  now  passing 
the  latter  through  a  coarse  filter  a  turbid,  ^t^itish  fluid  is  ob- 
tained containing  the  extracted  glycfii^^s  proved  by  giving 
a  red  color  with  solution  of  iodine.  The  substance  may  be  ob- 
tained as  a  whitish  amorphous  powder,  having  the  chemical  com- 
position of  stArch,  and  has  in  fact  been  termed  animal  starch. 

By  appropxiate  treatment  it  may  be  converted  into^ugu^by 
a  process  of  hydration  (CtHwO*  +  HfO  =  OtHitOi). 

If,  after  the  death  of  an  animal,  the  liver  be  kept  at  body 
temperature  for,  say,  an  hour,  very  little  glycogen  can  be  recov- 
ered from  it,  but  instead  abundance^  of  sugar.  These  facts  sug- 
gest that  the  sugar  present  represents  the  original  glycogen, 
and  that  the  converniun  has  been  effected  by  some  ferment, 
which  does  not  act  during  life,  though  why  no<  is  one  of  the"^ 
problems  ranking  with  the  non-digestion  of  the  stomach  by  its/ 
own  ferments,  etc. 

We  have  already  expressed  our  doubts  as  to  the  justifia- 
bility of  resorting  to  so  many  "  ferments  "  to  explaiu  the  facts 
of  physiology,  and  in  the  present  case  there  is  another  possible 
view  of  the  ntatter.  It  is  conceivable  that  the  conversion, 
under  these  circumstances,  of  the  glycogen  into  sugar,  may  be 
an  act  of  the  dying  protoplasm  of  the  liver-cells ;  and  there  are 
experimental  results  which  tend  to  strengthen  such  a  view. 

The  prir^ciiMtl  facts  an  to  the  storage  of  glycogen  in  the  liver 
may  be  briefly  stated  tlius : 

1.  Glycogen  has  been  found  in  the  liver  of  a  laurge  number 


m^ 


lammk^ 


p  to  addi- 
a  clearer 
I  we  shall 
Ten  fields 
Less  of  the 


.  The  for- 

aihed  how 
lecond. 
mals,  such 
;  the  warm 

them  into 
inding  in  a 
)w  passing 
luid  isob- 

by  giving 
may  be  ob- 
mical  com- 
al  starch. 
bo(sug^A>y 

jpt  at  body 
,n  be  recov- 
9  facts  sug- 
1  glycogen, 
le  ferment, 
one  of  the 
nach  by  i^ 

he  justifia- 
Lu  the  facts 
ler  possible 
conversion, 
jfar,  may  be 
id  there  are 
a  view, 
in  the  liver 

pge  number 


THE  METABOLISM  OF  THE  BODY. 


483 


of  groups  of  animals  including  some  invertebrates.  2.  Among 
mammals  it  is  most  abundant  when  the  animal  feeds  largely 
on  carbohydTates.  3.  It  is  found  in  the  liver  of  the  camivora, 
and  in  those  of  omnivora,  when  feeding  exclusively  on  flesh. 
4.  When  an  animal  starves  (does  not  feed),  the  glycogen  grad- 
ually disappears.  5.  A  fat-diet  does  not  give  rise  to  glycogen. 
6.  During  early  foetal  life  glycogen  is  found  in  all  the  tissues, 
but  later  it  is  restricted  more  and  more  to  the  liver,  though 
even  in  adults  it  is  to  be  found  in  various  tissues,  especially  the 
muscles,  from  which  it  is  almost  never  absent. 

From  the  facts  the  inference  is  plain  that  glycogen  is  formed 
from  carbohydrate  materials ;  or,  to  be  rather  more  cautious, 
that  the  formation  of  this  substance  is  dependent  on  the  pres- 
ence of  such  material  in  the  food.  Inasmuch  as  glycogen  oc- 
curs in  muscle,  it  does  not  follow,  from  the  fact  of  its  presence 
in  the  liver  of  carnivorous  animals,  that  it  is  manufactured 
from  proteid  substances,  though  this  is  not  more  difficult  to 
understand  chemically  than  the  formation  of  fat  from  this 
source  which  is  well  established. 

^  -Starch,  it  is  well  known,  occurs  abundantly  in-  plants,  and 
%ere  is  no  doubt  that  the  sugar  often  present  in  abundance  has 
starch  as  its  antecedent,  and  vice  versa.  Analogy,  then,  points 
.to  such  a  relation  between  carbohydrate  food  and  glycogen  for- 
mation on  the  one  hand,  and  reconversion  of  glycogen  into 
sugar  on  the  other.  And  recent  investigations  tend  to  show 
that  plant  metabolism  bears  a  greater  resemblance  to  that  of 
animals  than  was  till  recently  supposed,  thus  giving  greater 
force  to  the  argument  from  analogy,  though  this  ie  recognized 
as  fl^^nerally  a  dangerous  one. 

Assuming  this  relation  between  food-stuffs  and  glycogen  to 
hold,  the  question  arises.  How  is  the  substance  formed  by  the 
liver  ?  There  are  three  conceivable  methods :  1.  The  liver-cells 
may,  we  know  not  how,  simply  dehydrate  the  sugar  of  diges- 
tion as  carried  to  them  in  the  portal  blood.  2.  The  cells  may 
manufacture  glycogen  from  their  own  protoplasm,  in  which 
process  the  portal  sugar  is  in  some  way  used.  3.  The  liver-cells 
may  always  he  engaged  in  the  construction  of  glycogen  as  the 
gastric  cells  of  pepeinogen,  but  the  accumulation  or  removal  of 
the  substanbd  depends  on  the  oluuraoter  of  the  food  especially ; 
thus,  if  the  latter  abounds  in  carbohydrates,  the  blood  will  be 
well  supplied  with  sugar,  so  that  the  glycogen  need  not  undergo 
its  usual  conversion  into  that  substance.  None  of  these  views, 
haaJtweo^definitely  proved  to  be  the  correct  one. 


MUMfea 


iTijinl  Ar  ilJ^T'irili,  iiiin-rli^Vttrr 


484 


ANIMAL  PHYSIOLOGY. 


TIm  Vim  of  Olyoogen.— Whether  the  blood  of  the  hepatic  vein 
contains  more  sugar  than  that  of  the  portal  vein  has  long  been 
a  subject  of  controversy.  If  the  affirmative  could  be  established, 
it  would  be  pretty  clear  that  glycogen  stored  in  the  liver-cells 
was  transformed  into  sugar,  possibly  by  a  process  of  hydration. 
But,  considering  the  rapidity  of  the  blood-stream,  it  is  easy  to 
understand  that  a  large  amount  of  sugar  might  be  conveyed 


IfiXnMIMNNlnMft 


JM0Maicrfeie 


Vena 


&paUn 


Xivmph- dloiKl 


Lymphatle 


BUnivemOtttmueab, 
IvavMpaeef 


AUmentary  Uraet 


Fio.  88B.— Diagnun  intendad  to  iUiatrate  the  seneral  r«l«tian«  of  blood  and  lymph  to  milab- 
oUam  (nutriUoii) :  and  the  method  hy  wUcti  Uie  portal,  Ijmphatic,  and  seneral  Tenoaa 
■yatema  are  related  to  the  allmwiHiy  traet. 

into  the  general  circulation,  and  yet  the  blood,  whether  of  the 
hepatic  vein  or  of  other  parts,  contain  but  a  small  quantity  at 
any  one  time.  The  blood  is  kept  of  a  certain  fairly  constant 
composition,  both  by  the  action  of  the  excreting  organs  and  by 
the  withdrawal  from  it  of  supplies  for  the  tissues.  Moreover, 
that  correlation  of  functional  work  on  which  we  have  already 
insisted,  is  not  to  be  forgotten.  One  must  not  conceive  of  the 
liver-cells  or  any  others  doing  their  work  independently  of  the 
condition  of  their  fellow  cell-units  in  the  organic  common- 
wealth. We  mean  to  say  rhat  the  amount  of  glycogen  trans- 
formed to  sugar  will  depend  on  a  great  many  circumstances 
outside  of  the  liver  itself.  Such  aspects  of  the  case  have  been 
rather  overlooked.  According  to  uiother  theory,  glycogen  is 
an  intermediate  product  between  sugar  and  fat,  but  of  this 
there  is  very  little  evidence  indeed ;  and,  besides,  fat  formation 
is  otherwise  well  enough  accounted  for,  thouf'h,  of  course,  too 
much  stress  must  not  be  laid  upon  such  an  argcvnei  ^. 

jWhat  is  the  fate  of  the  transformed  glycogen  ?    What  be- 
(^mes  of  the  sugar  ?    We  can  answer,  negatively,  that  it  is  not 


jDBHiriaWiiii 


m 


1 


THE  METABOLISM  OP  THE  BODY. 


485 


vpatic  vein 
long  been 
stablished, 
liver-cells 
txydration. 
lis  easy  to 
conveyed 


t,  (((MM  ecO*, 
MS 


lymph  to  iii<<tab- 
general  vanou* 


ther  of  the 
quantity  at 
ly  constant 
;anB  and  by 
Moreover, 
ftve  already 
jeive  of  the 
intly  of  the 
iC  common- 
logen  trans- 
cumstances 
Q  have  been 
glycogen  is 
but  of  this 
,t  formation 
'.  course,  too 

What  be- 
hat  it  is  not 


used  up  in  the  blood,  it  is  not  oxidized  there;  but  by  what 
tissues  it  is  used  or  how  it  is  made  available  in  the  economy  is 
(_  a  subject  on  which  we  are  profoundly  ignorant.  The  presence 
of  so  much  glycogen  in  the  partiidly  developed  tissues  of  the 
fcBtus  points  to  its  importance,  and  suggests  its  being  a  crude 
material  which  is  laid  up  to  be  further  elaborated,  as  in  vege- 
tables, by  the  growing  protoplasm. 

Glycogen  being  so  generally  present  in  muscle,  its  diminu- 
tion running  parallel,  to  somo  extent  at  .'east,  with  the  func- 
tional activity  of  the  tissue,  it  is  clear  that  there  is  jome  im- 
portant purpose  served ;  but  here  again  we  inquire.  What  ? 

Pathologieal.— If  a  point  in  the  medulla  oblongata  of  a  rabbit, 
corresponding  nearly  or  completely  with  the  vaso-motor  center, 
be  punctured,  the  urine  will  in  a  few  hours  be  found  aug- 
mented in  quantity  and  containing  sugar. 

It  is  further  found  Uiat  the  quantity  of  the  latter  bears 
some  relation  to  the -diet  of  the  animal,  one  well  fed  on  carbo- 
hydrates having  more  sugar  in  the  urine  than  a  fasting  animal 
From  these  facts  it  has  been  concluded  that  the  nervous  system 
has  lost  a  customary  normal  influence  over  th^  glycogenic 
function,  either  directly  through  the  action  of  the  nerves  on 
the  liver-cells  6v  through  the  loss  of  tone  arising  from  injury 
to  the  vaso-motor  center.  Poisoning  by  carbonic  oxide  and  the 
administration  of  certain  drugs  also  causes  sugar  to  appear  in 
the  urine. 

The  syraptoms  resulting  from  puncture  of  the  medulla,  etc., 
have  been  spoken  of  as  "artificial  diabetes"— a  very  objection- 
able term  for  which  artificial  glycosuria  should  be  substituted. 
There  is  a  grave  and  often  fatal  disease  known  as  diabetes 
mellitus,  one  of  the  symptoms  of  which  is  the  appearance  often 
of  enormous  quantities  ol  grape-sugar  in  the  urine.  B^ut  all 
attempts  to  fi^m  the  hpihs  of  obscurity  which  surround  this 
malady  have  been  In  vadn.  It  would  seem  that  attention  has 
been  dirocted  too  exclusively  to  the  liver.  Cases  of  the  disease 
occur  in  which  at  the  poet  nortfim  examination  the  liver  may 
ba  perfectly  normal  in  appearnrxe,  or  either  hyperssmic  or 
aueemic. 

/It  seems  to  us  that  it  is  likely  that  the  disease  will  be  shown 
to  be  of  diverse  origins,  or  certaiidy  not  referable  to  one  organ 
solely  in  most  cases.  The  conclusion  that  the  nervous  system 
is  greatly  concerned,  both  in  directing  the  glycogenic  functions 
of  the  liver  and  in  the  disease  in  question,  seems  to  bo  un- 
doubted :  vaso-motor  effects,  when  present,  being  probably  of 


k^Jmi^^'^-ifii^M 


436 


ANIMAL  PHYSIOLOGY. 


secondary  importance.  We  doubt,  however,  if  the  results  of 
the  above-mentioned  experiment  warrants  any  inferences  as  to 
the  normal  glycogenic  functions. 

The  instructive  part  about  the  disease^iabetesjis  the  man- 
ner in  which  the  course  of  events  emphasize  the  importance 
of  co-ordination  among  the  vital  processes,  and  the  constant 
necessity  for  regulation  of  them  all  by  the  nervous  system. 
TPiajtetes  seems_tp  imply  that  these  processes  have  escaped  this 
joprmal  control  jmd^re^runninjjjriot._^  ~  "         ' 


/^ 


Metabolism  of  the  Spleen: 

The  physiological  significance  of  the  peculiar  structure  of 
this  organ,  though  not  yet  fully  understood,  is  much  plainer 


Fia.  MO.— V«rtio«l  Motkm  of  •  BnaU  wpertoW  pattioa  of  hnnMB  ■ptoM,  M«ii  wHh  1^ 
(Scbifer).   il,  perltoM*!  and  flbroua  oorwtac :  b,  fawbeaakB ;  c,  <*,  KaiplgiiiMi  oofpuwlM, 
in  one  01  whiofi  an  artery  «  Men  col  tniMTMWiy,  in  the  oUiFr,  kiagltiMUiially ;  d,  r  ' 
arteilfU  twifta ;  e,  spteen-T  <ulp. 


;d,bjeatod 


than  it  was  till  recently.  The  student  is  recommended  to  look 
carefully  into  the  histology  of  the  spleen,  especially  the  dis- 
tribution of  its  muscular  tissue  and  the  peculiarities  of  its 
bio*  'fl  -vascalar  system.  It  has  already  been  pointed  out  that 
the.'*e  is  little  doubt  that  leucocytes  are  manufactured  here  even 
in  ttio  adult,  possib'y  also  red  cells;  and  that  the  latter  are  dis- 
intt«grated,  and  the  resulting  substances  worked  over,  possibly 
by  this  organ  itself.  This  view  is  rendered  probable,  not  only 
by  microscopic  study  <A  the  organ,  but  by  a  chemical  examina- 


results  of 
ences  as  to 

is  the  man- 
importance 
le  constant 
)ti8  system, 
iscaped  this 


structtsre  of 
ach  plainer 


wn  with  km  powor 


»nded  to  look 
ally  the  dis- 
arities  of  its 
ted  out  that 
red  here  even 
latter  are  dis- 
)ver,  possibly 
ible.  not  only 
ical  examina- 


TBE  METABOLISM  OF  THE  BODY. 


487 


tion  of  the  splenic  pulp ;  for  a  ferruginous  proteid,  and  numer- 
ous pigments,  of  a  character  such  as  harmonizes  with  this  con- 
ception, are  found. 

The  fact  that  the  spleen-pulp  does  not  agree  in  composition 
with  either  blood  or  serum ;  that  it  abpunds  in  extractives  such 


fm.  an.-niiii  Mctioii  or 

vein  In  the  intcnttoM  c 
coptimdtir  wltk  otten,  . 
yttn.  DieihadMltMdiM 


■rain 


as  lactic,  butyric,  formic,  and  acetic  adds,  together  with  inosit, 
zanthin,  hypoxanthin,  leucin  and  uric  acid— points  to  its  being 


Fm.  SM.— PorUmi  of  naleea  of  oat,  aliowinx 
a  lynipliatio  r*- — 


jtalan  (lymphaUc)  oorpusole  (after  Cadiatj, 
rnnhM  of  apleeQ-pulp,  injected ;  C,  *rt«y 
*-  dear  spaoa  around  corpuaole  repraaents 


the  seat  of  a  ccwaplex  metabolism,  though  neither  the  changes 
thwBJselves  nor  their  purpose  are  well  understood,  x^--- 

Neverthel«B8,  i*  i»^t  be  admitted)  Ihat  to  recognize  this  was 
a  great  advance  «pon  the  view  Hhrnt  the  spleen  had  no  impor- 


438 


ANIMAL  PHTSIOLOGY. 


tant  function,  and  that  this  was  shown  by  the  removal  of  the 
organ  without  change  in  the  animal's  economyr^'A.,^ 

But  to  believe  that  there  are  no  such  changes,  and  to  have 
clear  proof  of  it,  are  two  different  things.  As  a  matter  of  fact, 
closer  study  does  show  that  in  some  animals  there  are  altera* 
tions  in  the  lymphatic  glands  and  bone-marrow,  which  wgans 
are  undoubtedly  manufacturers  of  blood-cells. 

These  changes  are  unquestionably  compensatory,  and  that 
other  similar  ones  corresponding  to  comparatively  unknown 
functions  c4  the  spleen  have  not  as  yet  been  discovered  is  owing 
likely  to  our  failures  rather  than  their  real  absence.  We  dwell 
for  a  moment  on  this,  because  it  illustrates  the  danger  of  the 
sort  of  reasoning  that  has  been  applied  in  the  case  of  this  and 
other  organs ;  and  it  shows  the  importance  of  recognizing  the 
force  of  the  general  principles  of  biology,  and  also  the  desira- 
bility of  refraining  from  drawing  conclusions  that  are  too  wide 
for  the  premises.  In  every  department  of  physiology  it  must 
be  more  and  more  recognized  that  what  is  true  of  one  group 
of  animals  is  not  necessarily  true  of  another,  or  even  of  other 
individuals,  though  the  differences  in  the  latter  case  are  of 
course  usually  lees  marked.  We  have  referred  to  this  be- 
fore, and  shall  do  so  again,  for  it  is  as  yet  but  too  little  con- 
sidered. 

Examinations  of  the  spleen,  carried  out  by  means  of  the  on- 
cograph, as  in  the  case  of  the  kidney,  reveal  the  foHowing  facts : 
1.  The  spleen  undergoes  slight  changes  in  volume,  correspond- 
ing to  the  respiratory  undulations  of  blood-pressure,  but  not,  as 
with  the  kidney,  to  each  heart-beat.  2.  The  spleen  experiences 
rhythmic  variations  in  size,  independent  of  the  general  blood- 
pressure.  It  will  be  borne  in  mind  that  the  splenic  arteries  end 
in  capillaries,  but  tliat  some  of  the  arterial  blood  finds  its  way 
possibly  from  the  capillaries  into  the  splenic  pulp,  from  which 
it  is  taken  up  by  veins  beginning  in  this  tissue. 

It  is  highly  probable,  then,  that  these  movements  serve  to 
propel  the  blood  that  has  found  its  way  into  the  pulp-tissue  on- 
ward into  the  veins ;  and  it  is  not  to  be  forgotten  that  among 
large  groups  of  invertebrates,  in  which  capillaries  are  wanting, 
a  not  very  unlike  method  of  carrying  on  the  general  circula- 
tion is  found ;  at  the  same  time,  we  may  suppose  that  such  an 
arrangement  of  blood-supply  and  removal  would  not  be  un- 
favorable to  splenic  metabolitim. 

There  is  one  fact  in  the  metabolism  of  the  spleen  that  de- 
serves special  notice,  though  we  can  not  indicate  all  its  bear- 


ral  of  the 

id  to  have 
ter  of  fact, 
are  altera* 
ich  organs 

J,  and  tliat 
r  unknown 
ed  is  owing 
We  dwell 
ager  of  the 
9f  this  and 
gnizing  the 
I  the  desira- 
ire  too  wide 
ogy  it  must 
:  one  group 
en  of  other 
case  are  of 
to  this  be- 
K)  little  con- 

« 

as  of  the  on- 
owing  facts: 
,  correspond- 
•e,  but  not,  as 
I  experiences 
sneral  blood- 
',  arteries  end 
finds  its  way 
,  from  which 

ents  serve  to 
alp4i8sue  on- 
n  that  among 
I  are  wanting, 
aeral  oiroula- 
)  that  such  an 
,d  not  be  un- 

pleen  that  de- 
e  all  its  bew- 


TBE  METABOLISM  OF  THB  BODY. 


489 


ings.    Uric  acid  is  found  in  the  spleen,  even  of  herbivorous 
animals,  though  not  in  their  urine. 


I  I  I  r'lu  I  I  I  I  I  I 


^bwlMt  of  Sbwd-pimRitn  ciinM. 

mu  I  I  I  I  I  I  I  I  I  UTTT 


r  r  I  III  I  I  I  I 


r  I  I  lU  I  I  I  I  I  I  I  I  lU  I  I  I  I  I  I  I  I  ILITT 


Vie.  tn.—XmdtiM  of  irieiilc  nutetiona  In  ito,  taken  wMi  tbe  onoocnph  (after  Roy),  tte 
tocrnaae  In  TMome  la  tiidloatwd  in  upiier  ourw  Iqr  tlw  aaoent  aiM  the  diminution  \iy  the 
doHent  Tlie  tndnc  uSom  ia  of  the  htood-pwaaure  aa  taken  in  caroUd  arteiy  <A  dog: 
The  k>wer  line  iMUoMiBa  ttme  maridnca. 

It  is  known  that  this  constituent  of  the  urine  is  increased  in 
intermittent  fever  (ague),  in  which  disease  the  spleen  is  often' 
greatly  enlarged.    The  vascular  engorgement  and  the  height- 
ened metabolism  of  the  spleen  seem  to  be  associated ;  and  the 
fact  that  the  uric-acid  diathesis  is  often  intensified  if  not  origi- 
nated by  overfeeding,  suggests  a  connection  between  the  spleen 
and  the  digestive  system  at  all  event&    Much  as  there  is  that^ 
remains  obscure,  we  think  it  can  not  be  doubted,  on  the  evi- ( 
dence  furnished,  that  the  spleen  must  serve  some  very  impor-( 
tant  purpose  in  the  economy,  apart  from  its  relations  to  the/ 
blood,  noticed  in  an  earlier  chapter. 

CJhe  dominion  of  the  nervous  system  over  tiie  spleen  is  evi- 
dent from  various  facts.  The  spleen  may  be  diminished  in  size 
either  generally  by  the  stimulation  of  the  vagus  or  splanchnic 
nerves  directly,  or  reflexly  through  stimulation  of  one  of  the 
afferent  nerves ;  and,  locally,  by  direct  application  of  the  elec- 
trodes to  the  surface  of  the  organ.  .Stimulation  of  the  medulla 
itself  also  leads  to  contraction  of  the  organ.  It  would  seem 
that  not  only  the  arteries  but  the  organ  as  a  whole  is  main- 
tained in  a  state  of  tonic  contraction  to  a  certain  extent  by  the 
agency  of  the  nervous  system.  Not  only  so,  but,  if  we  may 
judge  from  the  analogy  of  other  organs,  we  may  believe  that 
its  metabolism  is  directly  controlled  by  the  nervous  system.  ^^ 


rf.,>k-ytW 


440 


ANIMAL  PHYSIOLOGY. 


The  Construction  op  Fat. 

It  is  a  well-known  fact  that,  speaking  generally,  a  diet  rich 
in  carbohydrates  favors  fat  formation,  both  in  man  and  other 
animals ;  though  it  is  not  to  be  forgotten  that  many  persons 
seem  to  be  unable  to  digest  such  food,  or,  c.t  all  events,  to  as- 
similate it  so  as  to 'form  fat  to  any  great  extent.  Persous  given 
to  excessive  fat  production  are  as  frequently  as  not  sparing 
users  of  fat  itself. 

It  is  possible  in  man  and  probable  in  ruminants  that  fer- 
mentations may  occur  in  the  intestines  giving  rise  to  fatty  acids 
which  are  possibly  converted  into  fats  by  the  cells  of  the  villi 
or  elsewhere.  Certain  feeding  experiments  favor  the  view  that 
carbohydrates  may  be  converted  into  fat  or  in  some  way  give 
rise  to  an  increase  in  this  substance ;  for  it  is  to  be  borne  in 
mind  that  fat  may  arise  from  a  certain  diet  in  various  ways 
other  than  its  direct  transformation  into  this  substance  itself. 

There  are  certain  facts  that  make  it  clear  that  fat  can  be 
.formed  from  proteids :  1.  A  cow  will  produce  more  butter  than 
can  be  accounted  for  by  the  fat  in  her  food  alone.  2.  A  bitch 
which  had  been  fe<1  on  meat  produced  more  fat  in  her  milk 
than  could  have  been  derived  directly  from  her  food,  and  this, 
when  the  animal  was  gaining  in  weight,  which  is  usually  to 
be  traced  to  the  addition  of  fat ;  so  that  the  fat  of  the  milk 
was  not,  in  all  probability,  derived  from  that  of  the  dog's 
body;  and,  as  will  be  seen  presently,  can  be  accounted  for 
without  such  a  supposition.  3.  It  has  been  shown  by  analysis 
that  472  parts  of  fat  were  deposited  in  the  body  of  a  pig  for 
evOTv  100  in  its  food. 

rTnese  facts  of  themselves  su£Bce  to  show  that  fat  can  be 
fonned  from  proteid,  or  at  least  that  proteid  food  can  of  itself 
give  rise  to  a  metabolism,  resulting  in  fat  formation ;  and  the 
latter  is  probably  the  better  way  to  state  the  case  in  the  present 
condition  of  knowledge. 

An  examination  of  the  percentage  composition  of  proteid 
and  urea  renders  a  possible  construction  of  fat  from  proteid 
conceivable  and  in  harmony  with  other  better  known  physi- 
ological facts. 

Outon.      Hydrosaa     Nttrasen.       Oiyiieii.     Snl^ilMir. 

Proteid 5SO0  7-80  15*58  88-04         M8 

Uiwi aMK)  6-66  48-«7  a«-67 

It  will  be  seen  that,  if  we  assume  that  the  urea  discharged 
represents  the  whole  of  the  nitrogen  that  passes  through  the 


a  diet  rich 
.  and  other 
ny  persons 
ents,  to  as- 
•so  us  given  V 
ot  sparingj 

;s  that  fer- 
fatty  acids 
of  the  villi 
le  view  that 
le  way  give 
)e  home  in 
rious  ways 
^nce  itself. 

fat  can  he 
butter  than 

2.  A  bitch 
B  her  milk 
>d,  and  this, 
3  usually  to 
ot  the  milk 
f  the  dog's 
counted  for 
by  analysis 
of  a  pig  for 

I  fat  can  be 
can  of  itself 
on;  and  the 
1  the  present 

a.  of  proteid 
rom  proteid 
aown  physi- 


i8-04 


a  discharged 
through  the 


THE  METABOLISM  OP  THE  BODY. 


441 


body,  there  would  remain  for  disposal  otherwise  a  large  amount 
of  carbon,  for  there  is  nearly  three  times  as  much  of  this  ele- 
ment in  proteid  as  in  urea;  so  that  it  is  possible,  from  a  chemi- 
cal point  of  view,  to  understand  the  origin  of  fat  from  the  pro- 
teid food ;  but  too  much  importance  must  not  be  attached  to 
such  speculations. 

(That  fat  is  a  real  formation,  dependent  for  its  composition 
on  the  work  of  living  tissues,  is  clear  from  the  well-known  fact 
that  the  fat  of  one  animal  differs  from  that  of  another,  and  that 
it  preserves  its  identity,  no  matter  what  the  food  may  be,  or  in 
what  form  fat  itself  may  be  provided.  Certain  constituents  of 
the  animal's  fat  may  be  wholly  absent  from  the  fat  of  its  food, 
yet  they  appear  just  the  same  in  the  fat  produced  under  such 
diet.  Even  bees  can  construct  their  wax  from  proteid,  or  use 
unlike  substances,  as  sealing-wax. 

But  histological  examination  of  forming  adipose  tissue  itself 
throws  much  light  upon  t}  jject    Fat-«ells  are  those  in 

which  the  protoplasm  has  buuu  largely  replaced  by  fat.  The 
latter  is  seen  to  arise  in  the  former  as  very  smedl  glohules 


vUl 


\* 


Ite.  184.— KMiuBMr  rUimI  of  huniMi  femftto  (ptter  li6gMlm\  1,  rinflK,  or  dilatation  of  one  at 
lacttftoroDi  duota ;  S,  extnmitiM  ct  the  duels ;  8,  lobuka  of  glaiid ;  4,  nipple,  retracted  to 
cartar;  i,»niM. 


:^£&,y^^smiaiSi,ismm^ii^^s^mmS!is^mKMmmsi^^^mm>m 


mm 


ftmS^fii^rf^W^^^ 


441 


ANIMAL  PHYSIOLT'Cr. 


which  run  together  more  and  more  till  they  may  wholly  re- 
place the  original  protoplasm. 

The  history  of  the  mammary  gland  is,  perhaps,  still  more 
instructive.  In  this  case,  the  appearance  of  the  cells  during 
lactation  and  at  other  periods  is  entirely  different.    Fat  may 


Via.  BIB.— Sectloa  of  mammur  glaaA  (oMer  «a4-i 
Be  of  gland;  JV,  nlpiiM;  A,  adnt  of  gta_ 
folds  In  wide  mllk-duoti;  A,  wotioa  of  ^hiMtar 


milk-duct  in  nipple. 


,j)o<«oir (after TliaiilMaBr).    lfii,Mil>> 

X  m.4,  nilk-diKte ;  C,  milk-oifltemi ;  /, 

;  «,  exteriMl  lUn ;  It.  m.  d,  narroir 


he  seen  to  arise  within  these  cells  and  be  extruded,  perhaps  in 
the  same  way  as  an  Amoeba  gets  rid  of  the  waste  of  its  food. 
So  far  as  the  animal  is  conoemed,  milk  is  an  excretion  in  ar 
limited  sense. 


m 


perhaps  in 
if  its  f  dod. 
etion  in  a 


li»iii...iLjj.,ji»j7;?%»gj<;.j!;ii^i!^iV!!!»;ji^ii*«^  '"''"i 


'*._f^j  m  !■■  .!L'i  .'.•r''''M';>..  ..v'^"'-'.  V  "  '  w.'.'.'rr*'*— '•*•"';'■'■'■' ',■  yv-' 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


^ 


^ 


1.0 


1.1 


1^121    ■2.5 

122  ^^    ■■■ 

■tt  Itt   12.2 
•^    |£0    12.0 


|g5  |U,  MI.6 


-^ 


Photographic 

Sdenoes 

Carporation 


^ 


as  WKT  MAM  STRMT 

WIISTIt,N.V.  14SM 
(71«)t7a-4S0S 


^^-^^X 


KMKI 


iMlili 


•^^Kanif 


CIHM/ICMH 

Microfiche 

Series. 


CIHIVI/ICIVIH 
Collection  de 
microfiches. 


Canadian  Inatituta  for  Historical  IMicroraproductions  /  Inttitut  Canadian  da  microraproductions  historiquas 


rr 


L 


ia»a^aM#3«afl^^rf»s5iy4«igis»^^ 


THE  METABOLISM  OP  THE  BODY. 


443 


It  is,  in  the  nature  of  the  case,  impossible  to  follow  with 
the  eye  the  formation  and  separation  of  milk-sugar,  casein,  etc. 


Fio.  m.— I.  Adnw  from  nuunma  of  *  Mtch  irtieii  iBBcUve  (after  Beidenliain).    n.  DuHng 
MoreUoa  ot  milk,   a,  b,  mUk-^obules ;  e,  d, «,  cokNtrum-corpuaclM ;  /,  pale  cella. 

But  the  whole  process  is  plainly  the  work  of  the  cells,  and  in 
no  mechanical  sense  a  mere  deposition  of  fat,  etc.,  from  the 
blood;  and  the  same  view  applies  to  the  construction  of  fat  by 
connective  (adipose)  tissue. 


Fw.  Mr.  r».  888. 

r».  88i'.-BamMi  milk-RlolmlM,  from  «  hMltby  I]ria«-<B  womM^  eight  days  after  deUTM7 

n«.^  m^^oatram,  from  a  healttiur  tytag^lB  woman,  tweJte  howB  (rftw  delivery  (Funto). 
The  ofOMrumHwrpuKdea  aroluve  and  gran 
■ecretioii. 

Whether  fat,  as  such,  or  fatty  acid,  is  dealt  with  without 
being  built  up  into  the  protoplasm  of  the  cell,  is  not  known ; 
but,  taking  all  the  facts  into  the  account,  and  considering  the 
behavior  of  cells  generally,  it  seems  most  natural  to  regard 
the  construction  of  fat  asa  sort  of  secretion  or  excretion.  To 
suppose  that  a  living  cell  acts  upon  material  in  theblood  as  a 
workman  in  a  factory  on  his  raw  material,  or  even  as  a  chemist 


mmammmsBmmmsmm 


444 


ANIMAL  PHYSIOLOGY. 


does  in  the  lalwratory,  seems  to  be  too  crude  a  conception  of 
vital  processes.    Until  it  can  be  rendered  very  much  clearer 


Fio.  aw.— Mioranoole  aiipawMMW  of— I.  mfflc :  n,  eic«m :  m,  butter ;  IV,  ookMflruiB  at 
mMW  I V,  eoloatnim  of  oow  (aflar  TbaalioSH'). 

than  at  present,  it  is  not  safe  to  assume  that  their  chemistry  is 
our  )3hemistry,  or  their  methods  our  methods.  It  may  be  so ; 
but  let  us  not,  in  our  desire  for  simple  explanations  or  undue 
haste  to  get  some  sort  of  theory  that  apparently  fits  into  our 
own  knowledge,  assume  it  gratuitously,  in  the  absence  of  the 
clearest  proofs,  especially  when  our  fidlures  on  this  supposi- 
tion  are  so  nuiperous. 

e  may  say,  then,  that  fat  is  not  merely  selected  from  the 
blood,  but  formed  in  the  animal  tissues;  that  fat  formation 
may  take  place  when  the  food  consists  largely  of  carbohydrates, 
when  it  is  chiefly  proteid,  or  when  proteid  and  fatty. .  In  other 
words,  fat  results  from  the  metabolism  of  certain  cells,  which 
is  facilitated  by  the  consumption  of  carbohydrate  and  fatty 
food,  but  is  possible  when  the  food  is  chiefly  nitrogenous.  We 
must,  however,  recognize  differences  both  of  the  species  and 
the  individual  in  this  respect,  as  to  the  extent  to  which  one 
kind  of  food  or  the  other  most  favors  fat  formation  (excre- 
tion). The  use  of  the  adipose  tissue  as  a  packing  to  pre- 
vent undue  escape  of  heat  is  evident ;  but  more  important 


THE  METABOLISM  OP  THE  BODY. 


445 


ionception  of 
oiuch  clearer 


;  IV,  eoloalrum  of 

■  chemistry  is 
t  maybe  so; 
ons  or  undue 
f  fits  into  our 
bsence  of  the 
this  supposi- 

;ted  from  the 
at  formation 
Arbohydrates, 
bty. .  In  other 
a  cells,  which 
Ette  and  fatty 
>genou8.  We 
e  species  and 
to  which  one 
lation  (excre- 
3king  to  pre- 
tre  important 


purposes  are  probably  served,  as  will  appear  from  later  consid- 
erations. 

PathologiML— Corpulence,  or  excessive  fat  formation,  leading 
to  the  hampering  of  respiration,  the  action  of  the  muscles,  and, 
to  a  certain  extent,  many  other  functions  of  the  body,  does  not 
arise  usually  till  after  middle  life,  when  the  organism  has 
seen  its  best  day&  It  seems  to  indicate,  if  we  judge  by  the 
frequency  of  fatty  degeneration  after  disease,  that  the  proto- 
plasm stops  short  of  its  best  metabolism,  and  becomes  de- 
graded to  a  lower  rank;  for  certainly  adipose  tissue  does  not 
occupy  a  high  place  in  the  histological  scAle.  Many  persons 
given  to  excessive  fat  formation  are  fond  of  saccharine  and 
amylaceous  foods;  but  the  fact  that,  under  the  strictest  diet, 
the  abnormality  can  be  but  moderately  controlled,  shows  that 
the  main  point  is,  the  existence  of.  the  habit  of  certain  cells 
naturally  to  form  fat,  which,  in  disease,  becomes  exaggerated, 
or  is  taken  up  by  others  that  normally  have  little  share  in 
such  work.  Such  pathological  facts  throw  a  good  deal  of  light 
upon  the  general  nature  of  fat  excretion,  as  it  would  be  better 
to  term  it,  perhaps,  and  seem  to  warrant  the  view  that  we  have 
presented  of  the  metabolic-processes. 

yLlthough  the  nerves  governing  the  secretion  of  milk  have 
not  been  traced,  there  can  be  no  doubt  that  the  nervous  system 
controls  this  gland  also.  The  influence  of  the  emotions  on  both 
the  quantity  and  quality  of  the  milk  in  the  human  subject  and 
in  lower  animals  is  well  known.  There  seems  to  be  no  doubt 
that  milk  of  an  injurious  if  not  absolutely  poisonous  character 
may  be  formed  under  the  influence  of  depressing  or  unusually 
exciting  emotions,  as  grief,  rage,  etc.  We  know  less  about  the 
influence  of  the  nervous  system  in  fat  formation  elsewhere, 
though  it  is  well  enough  established  that  personsjpfow  thin 
under  worry  as  well  as  excessive  mentaland  physical  exertion. 
XnTiffie  lattefoase,  itis  not  improbable  that  the  bverwbrlced 
muscles  may  draw,  in  some  way,  on  the  stored  fat.  At  the 
same  time,  fat  formation  may  be  interfered  with,  and  be  an  ex- 
pression of  the  unnatural  conditions  generally  that  have  been 
established.  Such  cases  mre  too  complex  to  permit  of  being 
completely  unraveledT"- — 

Ow^anliv*.— While  breeders  recognize  certain  foods  as 
tending  to  fat  formation  and  others  to  milk  production,  it  is 
interesting  to  note  that  their  experience  shows  that  race  and 
individuality,  even  on  the  male  side,  tell.  The  same  conditions 
being  in  all  respects  observed,  one  breed  of'  cows  gives  more 


!ia3srssr:'T!?sT?mCT'tH??M!»ws^^ 


t.pi  IWWI 


'mmmmm 


446 


ANIMAL  PHYSIOLOGY. 


f  and  better  milk  than  another,  and  the  bull  is  himself  able  to 
{  transmit  this  peculiarity ;  for,  when  crossed  with  other  breeds, 
■  he  improves  the  milking  qualities  of  the  latter.  Individual 
\  differences  are  also  well  known. 


N 


The  Metabouc  Procbssbs  concerned  in  the  Formation 
OP  Urea,  Uttic  Acid,  Hippurio  Acid,  and  Allied 
Bodies. 

Creatin  is  represented  by  the  formula  C«HtNiOt,  and  crea- 
tinin  by  C«H,N,0— that  is,  the  latter  may  be  regarded  as  the 
firmer  dehydrated.  Creatinin  occurs,  as  we  have  seen,  in  urine, 
and  the  question  arises.  Is  the  creatin  of  muscle  the  antecedent 
of  the  creatinin  of  urine?  Creatin  when  injected  into  the 
blood  reappears  as  creatinin  in  the  urine ;  but  the  latter  sub- 
stance is  not  increased  by  exercise,  though  the  creatin  of  the 
muscles  is,  while,  like  urea,  creatin  is  augmented  by  a  proteid 
(flesh)  diet.  It  is  not  clear,  then,  that  the  creatin  of  muscle 
has  any  definite  relation  to  the  creatinin  of  urine.  But  crea- 
tin occurs  not  only  in  muscle,  but  in  a  variety  of  other  tis- 
sues, including  the  nervous;  in  fact,  it  maybe  regarded  as 
one  of  the  products  of  proteid  metabolism.  Putting  these 
facts  along  with  the  absence  of  urea  itself  from  muscle  and 
many  other  tissues,  there  is  some  probability  in  the  view 
that  creatin  is  one  of  the  aptecedents  of  urea;  possibly  it  is 
one  of  the  products  which  the  kidneys  directly  convert  into 

urea. 

There  are  several  facts  which  i>oint  to  the  liver  as  being 
the  seat  of  urea  formation:  1.  Leucin,  when  taken  in  large 
quantities,  reappears  in  the  urine  as  urea,  or,  at  all  events,  is 
followed  by  an  increase  in  the  excretion  of  urea  by  the  kid- 
neys. 2.  In  certain  diseases  of  the  liver  (acute  atrophy)  urea 
is  largely  replaced  in  the  urine  by  leucin  and  tyrosin.  Now, 
since  the  consumption  of  much  proteid  matter  is  soon  fol- 
lowed by  an  excess  of  urea  in  the  urine,  and  since  in  such 
cases  it  is  likely  that  a  good  deal  of  leucin  and  it&  compan- 
ion, tyrosin,  are  formed  in  the  digestive  tract,  which  we  may 
suppose  are  carried  directly  by  the  portal  blood  to  the  liver, 
the  conclusion  has  been  drawn  from  this  and  the  facts  just 
mentioned,  as  well  as  others,  that  the Jiver^isjk  fwrner^ 
(urea.  ,         "^ 


nself  able  to 

other  breeds, 

Individual 


Formation 
iND   Allied 


Oi,  and  crea> 
arded  as  the 
een,  in  urine, 
le  antecedent 
;ted  into  the 
le  latter  sub- 
reatin  of  the 

by  a  proteid 
in  of  muscle 
e.    But  crea- 

of  other  tis- 
»  regarded  as 
Putting  these 
1  muscle  and 

in  the  view 
possibly  it  is 

convert  into 

iver  as  being 
iken  in  large 
;  all  events,  is 
i  by  the  kid- 
itrophy)  urea 
rrosin.  Now, 
r  is  soon  f  ol- 
since  in  such 
i  it&  oompan- 
•hich  we  may 
to  the  liver, 
the  facts  just 
)  a  former  of 


THE  METABOLISM  OF  THE  BODY. 


Urea  may  be  prepared  artificially,  as  represented  by  the  f ol 
lowing  equations : 


1. 


^^<ONH.=  C0N,H4+  H,0. 


Ammaalum 
cartMunate. 


VrM. 


2.  CN.NH,  +  H,0  =  C0N.H4. 

CyMuunlde. 

3.  CN(ONH4)  =  CON,H4. 

Ammonltun 

Leucia  is  amido-caproic  acid  (CH,CH,CH,CH,CH(NH,) 
CO.H). 

Another  amido-acid,  glycin — 

AuldcMweac  add, 

when  introduced  into  the  digestive  tract,  gives  rise  to  an  in- 
crease of  the  urea  of  the  urine. 

It  will  be  seen  that  ammonia  compounds,  both  in  the  labora- 
tory and  apparently  in  the  body,  have  a  formative  relation  to 
urea ;  but  beyond  this  we  can  not  go  very  far  in  furnishing  a 
chemical  explanation  of  the  formation  of  urea  as  a  part  of  a 
series  of  metabolic  processes.  Do  the  kidneys  merely  pick 
out  from  the  blood  and  pass  on  into  the  urinary  tubules  the 
already  formed  urea — ^i.  e.,  eat,  so  to  speak,  and  then  discharge 
it,  Amoeba-Uke— or  do  they  manufacture  it  from  bodies  that 
have  gone  on  the  way  a  certain  distance  toward  urea  before 
they  reach  the  kidneys ;  or,  again,  do  they  form  urea  in  some 
such  way  as  the  mammary  gland  constructs  fat  ? 

If  the  ureters  be  tied,  the  renal  arteries  ligatured,  or  the 
kidneys  extirpated,  urea  accumulates  in  the  blood  and  tissues. 
This  might  be  explained  on  the  supposition  that  urea  formed 
elsewhere  was  not  eliminated;  or  that  some  body  related  to 
urea,  and  the  usual  transformations  of  which  are  completed 
in  the  kidneys,  under  these  unwonted  circumstances  becomes 
urea,  either  in  the  tissues  in  which  it  arose  or  elsewhere. 

VWe  can  not  pronounce  with  certainty  in  favor  of  any  one 
or  all  of  these  conceivable  methods.  We  may  perhaps  assume 
that  creatin  and  possibly  other  allied  bodies  are  antecedents  of 
urea;  that  the  leucin  and  perhaps  the  tyrosin  of  digestion  in 
some  way  give  rise  to  urea;  and  that  the  liver  and  possibly 
the  spleen  are  organs  in  which  a  portion  of  the  urea  is  formed ; 
that  a  part  of  the  urea  of  urine  is  simply  withdrawn  from  the 
blood  by  the  kidneys ;  but,  as  to  whether  any  part  is  made  by 


f 


448 


ANIMAL  PHYSIOLOGY. 


the  latter  in  either  of  the  senses  to  which  we  have  alluded 
above,  is  a  matter  on  which  there  is  very  little  evidence.  It  is 
perhaps  best  to  assume,  at  least,  the  possibility  of  the  truth  of 
both  of  them. 

Vrio  Add.— This  substance  can  be  oxidized  in  the  laboratory 

to  urea,  thus: 

C.H4N4O,  +  H,0  +  O  =  C4N,H.04  +  CN,H40, 

Uricaoid.  AlfcHTMi.  VrM. 


SO  that  it  has  been  assumed  that  uric  acid  in  the  body  is  a  stage 
short  of  urea,  and  this  seemed  the  more  plausible,  since  it  re- 
places the  latter  in  the  cold-blooded  animals.  But  this  is  not 
entirely  the  case,  for  in  the  frog  urea  is  found  in  the  urine, 
and  our  knowledge  of  this  secretion  in  most  of  them  is  very 
incomplete ;  moreover,  in  the  birds,  representing  the  very  great- 
est degree  of  activity  and  the  highest  oxidative  capacity,  uric 
acid  is  the  principal  nitrogenous  body  of  the  urine,  and  not 

urea. 

PftthdogiML— When  there  is  excessive  indulgence  by  man\ 
in  proteid  foods,  etc.,  the  uric  acid,  normally  small  in  quantity,  | 
is  increased  greatly,  and  may  give  rise  to  depositions  of  urates  / 
about  the  joints. 

It  seems  best  to  regard  uric  acid  as  the  result  of  proteid 
metabolism  when  of  a  certain  type,  and  urea  as  the  outcome 
of  the  vital  processes  of  animals  of  a  distinct  physiological 

type. 

Bvolutioii.— There  is  a  good  deal  of  paleontological  evidence 
which  points  to  a  phylogenetic  (ancestral)  relation  between 
birds  and  reptiles;  hence  the  many  points  of  functional  resem- 
blance between  these  groups  of  creatures  now  so  different  in 
form  and,  in  some  respects,  in  functions.  Tha  excessive  pro- 
duction of  uric  acid  (uric-acid  diathesis)  can  be  understood  m 
the  light  of  physiologic^  reversion.  It  is  well  known  that  this 
diathesis  is  hereditary— that  is  to  say,  the  metabolic  habit  of 
excessive  production  of  uric  acid  may  be  imparted  to  offspring. 

Eipporio  Add.— Among  the  herbivora  hippuric  acid  may  be 
said  to  replace  uric  acid.  In  the  laboratory  this  acid  may  be 
made  from  benaoic  acid  and  glyoocol  (glycin),  thus: 

C.H.COOH  +  igcX^H*  *=  OH.<gg[§0*C*^  ^  H.O. 

BmoioMld.  Otrdn.  Hlppurie  add. 

It  is  interesting  to  note  that,  when  benroio  acid  is  swallowed 
by  man,  hippuric  acid  appears  in  the  urine ;  and  it  is  said  that 


i&ve  alluded 

idenoe.    It  is 

the  truth  of 

le  laboratory 

CO, 

>dy  is  a  stage 
I,  since  it  re- 
it  this  is  not 
in  the  urine, 
them  is  very 
le  very  great- 
;apacity,  uric 
rine,  and  not 

ence  by  man 
1  in  quantity, 
ions  of  urates  / 

lit  of  proteid 
1  the  outcome 
physiological 

^cal  evidence 
*ion  between 
;tional  resem- 

0  different  in 
izcessive  pro- 
inderstood  in 
lown  that  this 
tx>lic  habit  of 
i  to  offspring, 
c  acid  may  be 
3  acid  may  be 
as: 

•^  +  H,0. 

Id. 

1  is  swallowed 
it  is  said  that 


THE  METABOLISM  OP  THE  BODY. 


449 


when  blood  containing  benzoic  acid  is  mixed  with  fresh  minced 
kidney  it  is  transformed  to  hippuric  acid.  Hay  contains  a  ben- 
zoic compound,  so  that  it  is  not  diflBcult  to  find  a  starting-point 
for  the  hippuric  acid  of  the  herbivora.  In  these  instances  it  is 
assumed  that  glycin  is  added  in  the  kidneys ;  but,  as  a  matter 
of  fact,  this  substance  has  not  as  yet  been  found  anywhere  in 
the  body,  though  it  is  possible  to  conceive  that,  like  peptone, 
it  might  be  formed  and  disappear  (be  used)  as  fast  as  gen- 
erated. 

(The  above  is  one  of  the  clearest  cases  favoring  the  view  that 
the  chemical  processes  of  the  body  do  really  very  much  resem- 
ble those  of  the  laboratory.  But,  considering  the  difficulty  as 
to  glycin,  and  that  the  liver  also  can  form  hippuric  acid  under 
similar  circumstances  (those  mentioned  above),  and  that  there 
are  several  laboratory  methods  for  the  synthesis  of  hippuric 
acid,  it  behooves  us  to  be  cautious  even  in  this  case,  the  chain 
of  facts  being  by  no  means  complete. 

Pt  the  origin  of  the  allied  bodies— xanthin,  etc.— or  their 
fate  and  purpose,  we  know  very  little.  Their  resemblance 
chemically  to  certain  alkaloids  in  tea,  coffee,  etc.,  is  suggestive. 
Are  they  natural  stimulantj  ? 

The  Study  of  the  Metabolic  Processes  by  other 

Methods. 

(it  will  be  abundantly  evident  that  our  attempts  to  follow 
the  changes  which  the  food  undergoes  from  the  time  of  its 
introduction  into  the  blood  until  it  is  removed  in  altered  form 
from  the  body  has  not  been  as  yet  attended  with  great  success. 
It  is  possible  to  establish  relations  between  the  ingesta  and  the 
egesta,  or  the  income  and  output  w!;  ch  have  a  certain  value. 
It  is  important,  however,  to  remeu;  ■  k-v  that,  when  quantitive 
estimations  have  to  be  made,  a  small  exror  in  the  data  becomes 
a  large  error  in  the  final  estimate;  one  uptrue  assumption 
may  vitiate  completely  all  the  conclusions. 

In  discussing  the  subject  we  shall  introduce  h  number  of 
tables,  but  it  will  be  remembered  that  the  results  obtained  by 
one  investigator  differ  from  those  obtained  by  another;  and 
that  in  all  of  them  there  are  some  deviations  from  strict  ac- 
curacy, so  that  the  results  must  be  regarded  as  only  approxi- 
mately correct.  It  is,  however,  we  think,  better  to  examine 
such  statistical  tables  of  Mialyses,  etc.,  than  to  rely  on  the 
mere  verbal  statement  of  certain  results,  as  it  leaves  mote 

i9 


litlUUJMWIIWIHI 


r= 


;■ 


460 


ANIMAL  PHTSIOLOOr. 


room  for  individual  judgment  and  the  assimilation  of  such 
ideas  as  they  may  suggest  outside  of  the  subject  in  hand. 

The  subject  of  diet  is  a  very  large  one ;  but  it  will  be  evi- 
dent on  reflection  that,  before  an  average  diet  can  be  prescribed 
on  any  scientific  grounds,  the  composition  of  the  body  and 
the  nature  of  those  processes  on  which  nutrition  generally 
depends  must  be  known.  Not  a  little  may  be  learned  by  an 
examination  of  the  behavior  of  the  body  in  the  absence  of  all 
diet,  when  it  may  be  said  to  feed  on  itself,  one  tissue  sup- 
plying another.  All  starving  animals  are  in  the  nature  of  the 
case  carnivorous. 


Composition  of  the  Mammalian  Body. 

Adult  man. 

New-bom  child. 

Skeleton 

Muscles.  

18-9 
41-8 
1-7 
7-3 
18-2 
GO 
ID 

17-7 
22-9 

Thoracic  viscera 

Abdominal  viscera. 

11-5 

Pat 

I  20-0 
16-8 

Skin 

Brain 

■^ 


I-  \ 


For  the  cat  an  analysis  has  yielded  the  following : 

Muscle  and  tendons 45*0  per  cent. 

Bones 147       " 

Skin 120       ** 

Mesentery  and  adipose  tissue 8*8       ** 

Liver 48       ** 

Blood  (escaping  at  death) 6'0       '* 

Other  organs  and  tissues 137       *' 

The  large  proportional  weight  of  the  muscles,  the  similarly 
large  amount  of  blood  they  receive,  which  is  striking  in  the 
case  of  the  liver,  also  ciuggest  that  the  metabolism  of  these 
structures  is  very  active,  and  we  should  expect  that  they 
would  lose  greatly  during  a  starvation  period.  It  is  a  matter 
of  common  observation  that  animals  do  lose  weight' and  grow 
thin  under  such  circumstances,  which  means  that  they  must 
lose  in  the  muscles  and  the  adipose  tissue.  Attempts  have  been 
made  to  determine  exactly  the  extent  to  which  the  various 
tissues  do  suffer  during  complete  abstinence  from  food,  and 
this  may  be  gathered  from  l^e  table  given  below. 

■tarfalUm. — A  cat  weighing  3,464  grammes  lost  before  deatii 
on  the  eight^nth  day  1,197  grammes  in  weight.    Of  this  about 


IvlC 


on  of  such 
hand. 

will  be  evi- 
9  prescribed 
e  body  and 
n  generally 
rned  by  an 
)sence  of  all 
I  tissue  sup- 
lature  of  the 


Mevr-born  child. 


17-7 

22« 

8-0 

11-5 

|2(M) 

15-8 


)  per  cent. 

r     " 


r     " 

the  similarly 
iriking  in  the 
liism  of  these 
3ct  that  they 

It  is  a  matter 
ght'and  grow 
lat  they  must 
upts  have  been 
5h  the  various 
rom  food,  and 
r. 

Bt  before  death 
Of  this  about 


THE  METABOLISM  OF  THE  BODY.  451 

204  grammes  (17  per  cent)  was  in  albuminous  matter;  132 
grammes  (11  per  cent)  loss  of  fat ;  863  grammes  loss  of  water,  71 
per  cent  of  the  total  body  weight. 

It  will  not  be  forgotten  that  about  three  fourths  of  the 
body  is  made  up  of  water,  so  that  the  loss  of  so  large  an 
amount  of  the  latter  during  starvation  is  not  wholly  inexpli- 
cable. 

In  the  case  of  another  cat  during  a  starvation  period  of  thir- 
teen days  734  grammes  of  solids  were  lost,  of  which  248  grammes 
were  fat  and  118  muscle — ^i.  e.,  about  one  half  of  the  total  loss 
was  referable  to  these  two  tissues  alone. 

The  other  tissues  lost  as  follows,  estimated  as  dry  solids : 

Adipose  tissue 97*0  per  cent. 

Spleen 631        ** 

Liver 56-6       " 

Muscles 30-2 

Blood 17-6       " 

Brain  and  spinal  cord 0*0       " 

It  will  be  observed  (a)  that  the  loss  of  the  fatty  tissue  was 
greatest,  nearly  all  disappearing ;  {b)  that  the  glandular  struct- 
ures were  next  in  order  the  greatest  sufferers;  (c)  that  after 
them  come  the  skeletal  muscles. 

Now,  it  has  been  already  seen  that  these  tissues  all  engage 
in  an  active  metabolism  with  the  exception  of  adipose  tis- 
sue. 

The  small  loss  on  the  part  of  the  heart,  which  is  still  less 
for  the  nervous  system,  is  especially  noteworthy.  Two  ex- 
planations are  possible.  On  the  one  hand,  we  may  suppose 
that  their  metabolism  is  active,  but  that  they  feed  in  some 
sense  on  the  other  tissues,  and  thus  preserve  themselves  from 
loss  of  substance.  But,  again,  we  have  seen  that  the  functional 
activity  of  the  nervous  system  is  not  accompanied  by  any  very 
marked  chemical  phenomena  that  we  have  succeeded  in  detect- 
ing, at  all  events;  and  litjtle  is  known  of  the_metabolism_or 
tha  heart  itse^.  Do  its  pulsations  fromlong  habit  go  on  with 
little  expenditure  of  energy,  as  is  the  case  with  the  automatic 
workman  engaged  in.  a  narrow  round  of  duty  ?  Has  the  nerv- 
ous system  in  the  course  of  its  evolution  acquired  the  power 
of  accomplishing  much,  like  persons  with  special  aptitudes, 
with  little  loss  of  energy  ?  It  is  not  possible  to  decide  exactly 
what  share  these  sevend  factors  may  take ;  though  that  they 
all  and  others  as  yet  unrecognized  do  share  in  the  general 
result  seems  probable.    The  loss  of  adipose  tissue  is  so  striking 


i 


':sss>¥.»fv>'ii'«aXumxM'mMM!Sm!mm'mAV^ 


453 


ANIMAL  PHTSIOLOOT. 


V 


that  we  must  regard  it  as  an  especially  valuable  storehouse  of 
energy,  available  as  required. 

When  we  turn  to  the  urine  for  information,  it  is  found  that 
in  the  above  case  27  grammes  of  nitrogen  were  excreted  and 
almost  entirely,  of  course,  in  the  form  of  urea ;  and  since  the 
loss  of  nitrogen  from  the  muscles  amounted  to  15  grammes,  it 
will  appear  that  more  than  one  half  of  the  nitrogenous  excreta 
is  traceable  to  the  metabolism  of  muscular  tissue.  It  has  been 
customary  to  account  for  the  urea  in  two  ways :  first,  as  derived 
from  the  metabolism  of  the  tissues  as  such,  and  continuously 
throughout  the  whole  starvation  period ;  and,  secondly,  from  a 
stored  surplus  of  proteid  which  was  assumed  to  be  used  up 
rapidly  during  the  early  days  of  the  fasting,  and  was  the  liutti8 
consumption  of  certain  investigators. 

OompMratiT*. — Experiment  has  shown  that  the  length  of 
time  during  which  different  groups  of  animals  can  endure  com- 
plete withdrawal  of  food  is  very  variable,  and  this  applies  to 
individuals  as  well  as  species.  That  such  differences  hold  for 
the  human  subject  is  well  illustrated  by  the  history  of  the  sur- 
vivors of  wrecks.  Making  great  allowances  for  such  devia- 
tions from  any  such  results  as  can  be  established  by  a  limited 
number  of  experiments,  it  may  be  stated  that  the  human  being 
succumbs  in  from  twenty-one  to  twenty-four  days;  dogs  in 
good  condition  at  the  outset  in  from  twenty-eight  to  thirty 
days;  small  m.ammals  and  birds  in  nine  days,  and  frogs  in 
nine  months.  ^Very  much  depends  on  whether  water  is  allowed 
or  not — ^lif e  lasting  much  longer  in  the  former  case.  The  very 
young  and  the  very  old  yield  sooner  than  persons  of  middle 
age.  It  has  been  estimated  that  strong  adults  die  when  they 
lose  ^  of  the  body  weight.  Well-fed  animals  lose  weight 
more  rapidly  at  first  than  afterward. 

Diet.— ^11  experiments  and  observations  tend  to  show  that 
an  animal  can  not  remain  in  health  for  any  considerable  period 
without  having  in  its  food  proteids,  fats,  carbohydrates,  and 
salt« ;  indeed,  sooner  or  later  deprivation  of  any  one  of  these 
will  result  in  death. 

Estimates  based  on  many  observations  have  been  made  of 
the  proportion  in  which  these  substances  should  enter  into  a 
normal  diet.  In  the  nature  of  the  case,  for  a  creature  like 
man  especially,  whose  adaptive  power  is  so  great  that  he  can 
learn  to  live  under  a  greater  variety  of  conditions  than  any 
other  animal,  any  figures  on  this  subject  must  be  interpreted 
as  being  but  a  very  general  statement  of  the  case. 


WUhJ- 


THE  METABOLISM  OF  THE  BODY. 


453 


rehouse  of 

found  that 
jreted  and 
1  since  the 
rammes,  it 
JUS  excreta 
[t  has  been 
as  derived 
•ntinuously 
dly,  from  a 
be  used  up 
IB  the  luxiis 

>  length  of 
endure  com- 
s  applies  to 
ceshold  for 
Y  of  the  sur- 
Buch  devia- 
by  a  limited 
luman  being 
ys;  dogs  in 
ht  to  thirty 
md  frogs  in 
«r  is  allowed 
e.    The  very 
tis  of  middle 
ie  when  they 
lose  weight 

to  show  that 

erable  period 

lydrates,  and 

one  of  these 

been  made  of 
I  enter  into  a 
creature  like 
it  that  he  can 
ons  than  any 
}e  interpreted 


We  give  another  series  of  tables,  founded  on  experiments 
by  different  investigators  from  which  a  number  of  conclusions 
may  be  drawn : 

The  Requirements  of  an  Adult  Man  for  Twenty-four  Hours. 


FOOD  IN  GRAXMES. 

At  n>M. 
(Flayfalr.) 

Moderate  work. 
(MotoMbott.) 

Laborloua  work. 

(Playfalr.) 

(V.  Pettenkofer 
and  V.  VoU.) 

Proteids 

70-87 

28-35 

810-20 

130 

84 

404 

165-92 

70-87 

567-50 

187 

Fats 

Carbohydrates , .   . . 

117 
852 

Ingesta  of  an  Adult  working  moderately  ( Vierordt). 


0 

H 

N 

O 

120  grammes  albumin,  containing 

64-18 

70-20 

146-62 

8-60 
10-96 
2033 

18-88 

28-84 

90  grammes  fats,  containing 

9-54 

880  mrammes  starch,  coataiiuuir 

162-85 

Total 

281-20 

80-10 

18-88 

200-78 

It  has  further  been  estimated  that  744  grammes  of  oxygen 
are  respired,  2,818  grammes  water  drunk,  and  32  grammes  of 
salts  consumed. 

The  total  ingesta  have  been  estimated  at  ^  of  the  body 
weight ;  and  the  daily  metabolism  of  the  body  is  calculated  as 
leading  to  the  transformation  of  6  per  cent  of  the  water,  6  per 
cent  of  the  fat,  1  per  cent  of  the  proteids,  and  4  per  cent  of 
the  salts  of  the  body. 

T^e  Egesta  of  an  Adult  working  moderately. 


H,0 

0 

H 

N 

o 

By  respiration 

Bv  transoiration 

880 

660 

1,700 

128 

248-8 

2-0 

0-8 

20H) 

•J  •  • 

*8-8' 
8-0 

t 

•  •  •  • 

16-8 
8-0 

65115 
T2 

By  urine 

.11-1 

By  foces 

12-0 

Total.. 

2,818 

281-2 

6-8 

18-8 

681-45 

If  .we  lay  down  the  rule  as  has  been  done,  that  the  nitrog- 
enous should  bear  the  proportion  of  1  to  3t-4i  of  non-ni- 
trogenous, an  inspection  of  the  following  analytical  table 
will  show  how  these  various  food-stuffs  conform  to  such  an 
estimate. 


mem»ibHm!X!'!s*^MmmiiiismMmimmiimam 


454 


ANIMAL  PHYSIOLOGY. 


For  the  herbivora  from  1  to  8-9  (some  claim  1  to  6J)  is  the 
estimated  ratio  of  nitrogenous  to  non-nitrogenous  foods : 


Nitro.  Non-nltro. 

Veal 10  1 

Hare's  flesh 10  2 

Beef 10  17 

Lentils 10  21 

Beans 10  22 

Peas 10  23 

Mutton 10  27 

Pork 10  80 

Cow's  mUk 10  80 


mtro.  Non-nitro. 

Human  milk. 10  37 

Wheaten-flour. 10  46 

Oatmeal 10  50 

Rye-meal. 10  .  57 

Barley-meal 10  57 

White  potatoes 10  86 

Blue  potatoes 10  115 

Ricfr. 10  123 

Buckwheat-meal 10  130 


One  investigator  estimates  that  in  order  to  get  the  one  hun- 
dred and  thirty  grammes  of  proteids  required  by  an  adult  man 
engaged  at  moderate  labor,  the  foUowirt?  proportions  of  differ- 
ent kinds  of  foods  must  be  eaten : 


Qnunmes. 

Cheese. 888 

Lentils 491 

Peas 582 

Beef. 614 

Eggs 968 


Orammes. 

Wheaten  bread 1,444 

Rice 2,562 

Rye-bread 2,875 

Potatoes.. 10,000 


One  conclusion  that  is  most  obvious  from  the  above  is  that, 
in  order  to  obtain  the  amount  of  proteids  needed  from  certain 
kinds  of  food,  enormous  quantities  must  be  eaten  and  digested ; 
and  as  there  would  be  in  such  cases  an  excess  of  carbohydrates, 
fats,  etc.,  unnecessary  work  is  entailed  upon  the  organism  in 
order  to  dispose  of  this. 


Feeding  Experiments  {Ingesta  and  Egesta). 

If  all  that  enters  the  body  in  any  form  be  known,  and  all 
that  leaves  it  be  equally  well  known,  conclusions  may  be  drawn 
in  regard  to  the  metabolism  the  food  has  undergone.  The  pos- 
sible sources  of  fallacy  will  appear  as  we  proceed. 

The  ingesta,  in  the  widest  sense,  include  the  respired  air  as 
well  as  the  food ;  though  from  the  latter  must  be  subtracted 
the  waste  (undigested)  matters  that  appear  in  the  faeces.  The 
ingesta  when  analyzed  include  carbon,  hydrogen,  oxygen,  ni- 
trogen, sulphur,  phosphorus,  water,  and  salts,  their  source 
being  the  atmosphere  and  the  food-stuffs.  / 

The  egesta  the  same,  and  chiefly  in  the  form  of  carbonic  an- 
hydride, of  water  from  the  lungs,  skin,  alimentary  canal,  and 


THE  METABOLISM  OF  THE  BODT. 


455 


o  5i)  is  the 
tods: 

itro.    Non-nitro. 
10  87 


10 

10 

10. 

10 

10 

10 

10 

10 


46 

50 

57 

57 

86 

115 

123 

180 


lie  one  hun- 
i  adult  man 
ns  of  differ- 


Orammes. 

1,444 

2,562 

2,875 

10,000 


bove  is  that, 
from  certain 
id  digested ; 
rbohydrates, 
organism  in 


rfa). 

own,  and  all 
lay  be  drawn 
10.    The  pos- 

»spired  air  as 
>e  subtracted 
f eeces.  The 
,  oxygen,  ni- 
their  source 

carbonic  an,- 
ry  canal,  and 


kidneys,  of  salts  and  water  from  the  skin  and  kidneys,  and  of 
nitrogen,  chiefly  as  urea  almost  wholly  from  the  kidneys.  Usu- 
ally in  experimental  determinations  the  total  quantity  of  the 
nitrogen  of  the  urine  is  estimated.  If  free  nitrogen  plays  any 
part  in  the  metabolic  processes  it  is  unknown. 

A  large  number  of  feeding  experiments  have  been  made  by 
different  investigators,  chiefly,  though  not  exclusively,  on  the 
lower  animals.  Some  such  method  as  the  following  has  usu- 
ally been  pursued :  1.  The  food  used  is  carefully  weighed  and  a 
sample  of  it  analyzed,  so  that  more  exact  data  may  be  obtained. 
2.  The  amount  of  oxygen  used  and  carbonic  anhydride  exhaled, 
as  well  us  the  amount  of  water  given  off  in  any  form,  is  esti- 
mated. 3.  The  amount  of  the  nitrogenous  excreta  is  calculated, 
chiefly  from  an  analysis  of  the  urine,  though  any  loss  by  hair, 
etc.,  is  also  to  be  taken  into  account. 

It  has  been  generally  assumed  that  the  nitrogen  of  the  ex- 
creta represents  practically  the  whole  of  that  element  entering 
the  body.    This  has  been  denied  by  some  investigators. 

The  respiratory  products  have  been  estimated  in  various 
ways.  One  consists  in  ineasuring  the  quantity  of  oxygen  sup- 
plied to  the  chamber  in  which  the  animal  under  observation  is 
inclosed,  and  analyzing  from  time  to  time  samples  of  the  air  as 
it  is  drawn  through  the  chamber ;  and  on  these  results  the  total 
estimates  are  based. 

It  will  appear  that  even  errors  in  calculating  the  composi- 
tion of  the  food— and  this  is  very  variable  in  different  samples, 
e.  g.,  of  flesh ;  or  any  errors  in  the  analysis  of  the  urine,  or  in 
the  more  difficult  task  of  estimating  the  respiratory  products, 
may,  when  multiplying  to  get  the  totals,  amount  to  serious  de- 
partures from  accuracy  in  the  end ;  so  that  all  conclusions  in 
such  a  complicated  case  must  be  drawn  with  the  greatest  cau- 
tion. But  it  can  not  be  doubted  that  such  investigations  have 
proved  of  much  practical  and  some  scientific  value.  The  labor 
they  entail  is  enormous. 

Proteid  Ibtaboliim.— If  we  conceive  of  a  structural  unit  or 
cell  as  made  up  of  a  genuine  protoplasni  constituting  its  mesh-' 
work  and  holding  in  the  interstices  certain  substances  that  are 
not  part  of  itself,  strictly  speaking,  the  question  arises,  Are 
these  latter  used  up  in  the  metabolic  ptocess  as  such,  or  do  they 
become  a  part  of  the  true  protoplasm  before  they  undergo  the 
changes  referred  to  above?  Some  writers  speak  of  "organ 
albumin  "  and  "  circulating  albumin,"  and  they  believe  that  the 
latter,  by  which  is  meant  the  proteid  material  found  every- 


Mnm 


MiMMinigiiilil 


456 


ANIMAL  PHYSIOLOOT. 


where  in  the  fluids  of  the  body,  as  opposed  to  the  former  as 
constituting  organized  tissues,  undergoes  changes  of  a  retro- 
grade kind  without  ever  becoming  organ  albumin,  while  the 
term  luxus  consumption  was  applied  to  the  metabolism  of  pro- 
teids  in  the  blood.  The  latter  is  not  now  believed  to  occur. 
But  whether  a  portion  of  the  urea  that  represents,  in  the  main, 
the  results  of  proteid  metabolism  is  not  derived  from  the 
metabolism  of  the  material  in  the  interspaces  of  the  tissues 
(circulating  proteids  on  which  the  cells  are  supposed  to  act 
and  in  which  they  effect  changes  without  making  these  pro- 
teids a  part  of  themselves),  is  uncertain. 

Hitrogenovf  Equililnriiiiii. — It  is  possible  to  so  feed  an  animal, 
say  a  dog,  that  the  total  nitrogen  of  the  ingesta  and  egesta 
shall  be  equal ;  and  this  may  be  accomplished  without  the  ani- 
mal losing  or  gaining  weight  appreciably  or  again  while  he  is 
gaining.  If  there  be  a  gain,  it  can  usually  be  traced  to  the 
formation  of  fat,  so  that  the  proteid,  we  may  suppose,  has 
been  split  up  into  a  part  that  is  constructed  into  fat  and  a 
part  which  is  represented  by  the  urea,  the  fat  being  either  used 
up  or  stored  in  the  body.  Moreover,  an  analysis  of  a  pig  that 
had  been  fed  on  a  fixed  diet,  and  a  comparison  made  with  orte 
of  the  same  litter  killed  at  the  commencement  of  the  experi- 
mentj  showed  that  of  the  dry  nitrogenous  food  only  about 
seven  per  cent  in  this  animal  and  four  per  cent  in  the  sheep 
had  been  laid  away  as  dry  proteid.  It  is  perfectly  plain,  then, 
that  proteid  diet  does  not  involve  only  proteid  construction 
within  the  body. 

Compuratiye.— The  amount  of  flesh  which  a  dog,  being  a  car- 
nivorous animal,  can  digest  and  use  for  the  maintenance  of  his 
metabolio  processes  is  enormous ;  though  it  has  been  learned 
that  ill-nouirished  dogs  can  not  even  at  the  outset  of  a  feeding 
experiment  of  this  kind  maintain  the  equilibrium  of  their  body 
weight  on  a  purely  flesh  diet  (fat  being  excluded).  They  at 
once  commence  to  lose  weight— i.  e.,  they  draw  upon  their  own 
limited  store  of  fat. 
-  *  The  digestion  of  herbivora  being  essentially  adapted  to  a 
vegetable  diet,  they  can  not  live  at  all  upon  flesh,  while  a  dog 
can  consume  for  a  time  without  manifest  harm  i^  to  ^  of  its 
body-weight  of  this  food. 

Man,  when  fed  exclusively  on  meat  soon  shows  failure,  he 
being  unable  to  digest  enough  to  supply,  the  needed  carbohy- 
drates, etc.  But  the  large  amount  of  urea  in  the  urine  of  car- 
nivorous animals  generally,  and  the  excess  found  in  the  urine 


■MMMMMMMTM 


THE  METABOLISM  OF  THE  BODV. 


457 


former  as 
if  a  retro- 
while  the 
im  of  pro- 
to  occur, 
the  main, 
from  the 
ihe  tissues 
sed  to  act 
these  pro- 

an  animal, 
Eind  egesta 
at  the  ani- 
rhile  he  is 
ced  to  the 
ppose,  has 
I  fat  and  a 
either  used 
a  pig  that 
iewith  oiie 
the  experi- 
only  about 
I  the  sheep 
ilain,  then, 
mstruction 

>eing  a  car- 
lance  of  his 
)en  learned 
)f  a  feeding 
their  body 
).  They  at 
1  their  own 

apted  to  a 

nrhile  a  dog 

to  ^  of  its 

failure,  he 
id  oarbohy- 
rine  of  car- 
n  the  urine 


of  man  when  feeding  largely  on  a  flesh  diet,  show  that  .the  pro- 
teid  metabolism  is  under  such  circumstances  very  active. 

It  is  also  a  well-known  observation  that  carnivorous  ani- 
mals (dogs)  are  more  active  and  display  to  a  greater  extent 
their  latent  ferocity,  evidence  of  their  descent  from  wild  car- 
nivorous progenitors,  when  like  them  they  feed  very  largely  on 
flesh.  The  evidence  seenis  to  .point  pretty  clearly  to  the  con- 
clusion that  a  nitrogenous  (flesh)  diet  increases  the  activity  of 
the  vital  processes  of  the  body,  and  e>^cially  the  proteid  me- 
tabolism. 

Some  have  explained  this  result  on  the  assumption  that 
such  diet  led  to  an  increase  in  the  red  corpuscles  of  the  blood, 
and  hence  in  the  oxygen-supply ;  but  mere  abundance  of  sup- 
ply will  never  of  itself  explain  results  in  a  living  organism.  It 
may  be  and  probably  is  true  that  such  a  diet  augments  the 
activity  of  the  oxidative  processes,  but  the  reason  of  this  lies 
deeper,  we  think,  than  the  explanations  as  yet  offered  assume. 
That  an  excess  of  proteids  may  be  stored,  as  it  seems,  is  true  of 
fats  and  carbohydrates,  to  be  used  in  the  hour  of  need,  seems 
not  improbable,  though  this  has  not  as  yet  been  shown  to  be 
the  case.  But  in  all  these  considerations  it  must  be  borne  in 
mind  that  the  metabolic  processes  go  on  in  the  tissues  and  not 
in  the  blood,  and  probably  not  in  the  lymph.  Not  that  these 
fluids  (tissues)  are  without  their  own  metabolic  processes  for 
and  by  themselves ;  but  what  is  meant  to  be  conveyed  is  that 
the  metabolic  processes  of  the  body  generally  do  not  take  place 
in  the  blood. 

Hm  Vffeoti  of  Oektine  in  tlis  Diet.— Actual  experiment  shows 
that  this  substance  can  not  take  the  place  of  proteid,  though  it 
also  makes  it  evident  that  less  of  the  latter  suffices  when  mixed 
with  a  certain  proportion  of  gelatine ;  and  it  has  been  suggested 
that  it  is  split  up  into  a  fatty  portion  and  urea,  and  that  it  thus, 
by  aiding  in  the  formation  of  fat,  preserves  some  of  the  proteid 
for  other  uses  than  fat  construction.  This  theory,  however,  is 
not  well  substantiated.  It  will  be  borne  in  mind  that  ordinary 
flesh  contains,  as  we  find  it  naturally  in  the  carcass,  not  only 
some  fat,  but  a  good  deal  of  fibrous  tissue,  which  can  be  con- 
verted by  heating  into  gelatine. 

Vkto  and  OurboliydntM. — It  is  a  matter  of  common  observa- 
tion and  of  more  exact  experiment  that  even  a  carnivorous  ani- 
mal thrives  better  on  a  diet  of  fat  and  lean  meat  than  on  lean 
flesh  alone.  Thus,  it  has  been  found  that  nitrogenous  equi- 
librium was  as  readily  established  by  a  due  mixture  of  fat  and 


I 


I 


MMMMa 


458 


ANIMAL  PHYSIOLOGY. 


i";. 


lean  as  upon  twice  the  quantity  of  lean  flesh  alone.    It  is  plain, 
then,  that  the  metabolism  is  actually  slowed  by  a  fatty  diet. 
When  an  animal  is  given  but  little  fat,  none  whatever  is  laid 
up,  but  all  the  carbon  of  the  fat  can  be  accounted  for  in  the 
excreta,  chiefly  as  carbonic  anhydride.    Again,  the  fatty  por- 
tion remaining  constant,  it  has  been  found  that  increasing  the 
proteid  leads  not  to  a  storage  of  the  carbon  of  the  proteid  ex- 
cess, but  to  an  increased  consumption  of  this  element.    It  is 
then  possible  to  understand  how  excessive  consumption  of  pro- 
teids  may  lead,  as  seems  to  be  the  case,  to  the  disappearance  of 
fat  and  loss  of  weight,  so  that  a  proteid  diet  increases  not  only 
nitrogenous  but  non-nitrogenous  metabolism.    That  carbohy- 
drates mixed  with  a  due  proportion  of  the  other  constituents 
of  a  diet  do  increase  fat  formation  is  well  established ;  though 
there  is*  no  equally  well-grounded  explanation  of  how  this  is 
accomplished.    Upon  the  whole,  it  seems  most  likely  that  fat 
can  be  directly  formed  from  carbohydrates,  or,  at  all  events, 
that  they  directly  give  rise  to  fat  if  they  are  not  converted 
themselves  into  that  substance. 

Comparative.— It  is  found  that  there  are  relations  between 
the  food  used  and  the  quantity  of  carbonic  dioxide  expelled 
which  are  instructive.  The  formula  following  show  the  amount 
of  oxygen  necessary  to  convert  a  starch  and  a  fat  into  carbonic 
anhydride  and  water : 

1.  C.H..O,  +  Q„  =  6(CO,)4-MH.O). 

2.  C«HmO,  -f  Om.  =  67(00.)  +  62(H.O). 

It  will  be  observed  that  in  the  first  case  the  oxygen  used  to 
oxidize  the  starch  has  all  reappeared  as  CO.,  while  in  the  sec- 
ond only  1 14  parts  out  of  160  so  reappear.  As  a  matter  of  fact, 
more  of  the  oxygen  used  does  in  herbivora  reappear  as  CO,, 
and  less  as  water,  while  the  reverse  holds  for  the  carnivora,  the 
proportion  being,  it  is  estimated,  as  from  90  to  60  per  cent. 
This  is  to  be  explained  by  the  character  of  the  fo6d  in  each 
instance,  for  this  relation  no  longer  holds  during  fasting,  when 
the  herbivorous  animal  becomes  carnivort)us  in  the  sense  that 
it  consumes  its  own  tissues. 

To  most  persons  the  carbohydrates  are  more  digestible  than 
fats,  though  they  have  less  potential  energy,  as  will  shortly 

be  seen. 

TlM  BfliNte  of  8a]l%  Wat«r,  «|o.,  in  tlw  Biet— We  have  already 
considered  how  salts  in  the  form  of  condiments  may  beneficially 
influence  the  digestion ;  but,  when  we  come  to  inquire  as  to  the 


It  is  plain, 
fatty  diet, 
ver  is  laid 
for  in  the 
fatty  por- 
reasing  the 
proteid  ex- 
tent. It  is 
lion  of  pro- 
3earance  of 
es  not  only 
A  carbohy- 
onstituents 
Bd;  though 
how  this  is 
ily  that  fat 
all  events, 
;  converted 

ns  between 
de  expelled 
the  amount 
ito  carbonic 


gen  used  to 
e  in  the  sec- 
ktter  of  fact, 
tear  as  COt, 
.rnivora,  the 
SO  per  cent, 
odd  in  each 
usting,  when 
e  sense  that 

restible  than 
will  shortly 

lave  already 
'  beneficially 
lire  as  to  the 


THE  METABOLISM  OP  THE  BODV. 


459 


part  they  play  when  introduced  into  the  blood,  we  soon  find 
that  our  knowledge  is  very  limited. 

Sulphur,  and  especially  phosphorus,  seem  to  have  some  im- 
portant use  which  quite  eludes  detection.  It  is  important  to 
remember  that  certain  salts  are  combined  with  proteids  in  the 
body,  possibly  to  a  greater  extent  than  we  can  learn  from  the 
mere  analysis  of  dead  tissues. 

Pafhokgiiwl.— The  withdrawal  of  any  of  the  important  salts 
of  the  body  soon  leads  to  disease,  clear  evidence  in  itself  of  their 
great  importance.  This  is  notably  the  case  in  scurvy,  in  which 
disease  the  blood  seems  to  be  so  disordered  and  the  nutrition 
of  the  vessel-walls  so  altered  that  the  former  (even  some  of  the 
blood-cells)  passes  through  the  latter. 

Wstor. — The  use  of  water  certainly  has  a  great  influence 
over  the  metabolic  processes  of  the  body.  The  temporary  ad- 
dition or  withdrawal  of  even  a  few  ounces  of  water  from  the 
regular  supply  of  a  dog  in  the  course  of  a  feeding  experiment 
greatly  modifies  the  results  obtained  for  the  time.  It  is  well 
known  that  increase  of  water  in  the  diet  leads  to  a  corresix)nd- 
ing  increase  in  the  amount  of  urea  excreted.  It  is  likely  that 
even  yet  we  fail  to  appreciate  the  great  part  which  water  plays 
in  the  animal  economy. 


y 


The  Energy  of  the  Animal  Body. 

As  already  explained,  we  distinguish  between  potential  or 
latent  and  actual  energy.  All  the  energy  of  the  body  is  to  be 
traced  to  the  influence  of  the  tissues  upon  the  food.  Energy 
may  be  estimated  as  mechanical  work  or  as  heat,  and  the 
one  may  be  converted  into  the  other.  All  the  processes  of 
the  organism  involve  chemical  changes,  and  a  large  propor- 
tion of  these  are  of  the  nature  of  oxidations ;  so  that,  speak- 
ing broadly,  the  oxidations  of  the  animal  body  are  the  sources 
of  its  energy ;  and  in  estimating  the  quantity  of  energy,  either 
as  heat  or  work,  that  a  given  food-stuff  will  produce,  one  must 
consider  whether  the  oxidative  processes  are  complete  or  par- 
tial •  thus,  in  the  case  of  proteid  food,  if  we  suppose  that  the 
urea  exci-eted  represents  the  form  in  which  the  oxidative  pro- 
cesses end  or  are  arrested,  we  must,  in  estimating  the  actual 
energy  of  the  proteid,  subtract  the  amount  of  energy  that 
would  be  produced  were  the  urea  itself  completely  oxidized 
(burned). 

If  the  amount  of  heat  that  a  body  will  produce  in  its  com- 


HMMh 


MIMM 


ANIMAL  PHYSIOLOGY. 


bustion  be  known,  then  by  the  law  of  the  conversion  and  equiv- 
alence of  energy  the  mechanical  equivalent  can  be  estimated  in 
that  particular  case. 

The  heat-producing  power  of  different  substances  can  be 
directly  learned  by  ascertaining  the  extent  to  which,  when  fully 
burned  (to  water  and  carbonic  anhydride),  they  elevate  the 
temperature  of  a  given  volume  of  water ;  and  this  can  at  once 
be  translated  into  its  mechanical  equivalent  of  work,  so  that 
we  may  say  that  one  gramme  of  dry  proteid  would  give  rise  to 
a  certain  number  of  gramme-degrees  of  heat  or  kilogramme- 
metres  of  work.  A  few  figures  will  now  show  the  relative 
values  of  certain  food-stuffs : 


' 


1  gramme  proteid 

1  gramme  urea. 

Available  energy  of  the  proteid 


Gram.-deg. 


5,108 
785 


4368 


Kilomet. 


3,161 
811 


1,850 


The  reason  of  the  subtraction  has  been  explained  above. 

Taking  another  diet  in  regard  to  which  the  estimates  differ 
somewhat  from  those  given  previously,  but  convenient  now  as 
showing  how  equal  weights  of  substances  produce  very  dif- 
ferent amounts  of  energy,  we  find  that — 


KilMnet. 


100  grammes  proteid  yield 
100  grammes  fat  yield. . . . , 
240  grammes  starch  yield. 

ToUl 


185,000 
884,100 
307,080 

966,780 


In  other  words,  nearly  a  million  kilogramme-metres  of  en- 
ergy are  available  from  the  above  diet  for  one  day,  provided 
it  be  all  oxidized  in  the  body. 

(Food^stuffs,  then,  with  the  oxygen  of  the  air,  are  the  body's 
sources  of  energy.  What  are  the  forms  in  which  its  expendi- 
ture appears  ?  We  may  answer  at  once,  heat  and  mechanical 
work ;  for  it  is  assumed  that  internal  movements,  as  those  of 
the  viscera,  and  all  the  friction  of  the  body,  all  its  molecular 
motion,  all  secretive  processes,  are  to  be  regarded  as  finally 
augmenting  the  heat  of  the  body.  Heat  is  lost  by  the  skin, 
lungs,  urine,  and  feeces. 


■«it^ 


a  and  equiv- 
estimated  iu 

nces  can  be 
1,  when  fully 

elevate  the 
i  can  at  once 
rork,  so  that 
I  give  rise  to 
kilogramme- 

the  relative 


Kilomet. 

a,iot 

811 

1,850 

}d  above, 
imates  differ 
nient  now  as 
ice  very  dif- 

'• 

Kilmnet. 

185,000 
884,100 
807,080 

066,780 

m 


metres  of  en- 
lay,  provided 

ire  the  body's 
I  its  expendi- 
d  mechanical 
ts,  as  those  of 
its  molecular 
led  as  finally 
5  by  the  skin, 


THE  METABOLISM  OF  THE  BODY. 


461 


The  amount  of  work  which  a  man  or  other  animal  can  do 
on  a  given  diet  may  be  estimated  without  the  same  sources  of 
fallacy  as  attend  the  calculation  of  the  heat  expenditure ;  for, 
when  an  animal  is  confined  in  a  calometric  chamber,  the  con- 
ditions of  the  normal  metabolism  are  not  observed. 

The  Sources  of  Muscular  Energy. 

EsperimenteL— Two  physiologists  (Fick  and  Wislicenus)  as- 
cended a  mountain,  noting  the  conditions  under  which  their 
metabolism  was  performed,  and  drew  certain  conclusions  in  re- 
gard to  the  question  now  being  considered.  They  lived  exclu- 
sively on  a  non-nitrogenous  diet  while  the  work  was  being  done, 
and  estimated  the  amount  of  urea  excreted  at  the  same  time. 
Assuming  that  the  urea  does  represent  the  proteid  metabolism 
(oxidation)  which  bore,  of  course,  a  definite  relation  to  the 
energy  available,  it  was  found  that  in  the  case  of  each  of  them 
this  was  only  about  half  enough  to  account  for  the  work  done. 
Even  making  large  allowances  for  error  in  the  estimates,  if 
this  experiment  is  to  be  trusted  at  all,  it  is  plain  that  the 
energy  of  the  muscles  of  the  body  is  not  derivable  from  their 
proteid  metabolism ;  and  there  are  other  facts  which  point  in 
the  same  direction. 

It  is  found,  when  an  isolated  muscle  is  studied,  that  its 
continued  contraction  does  not  produce  nitrogenous  bodies,  but 
very  different  ones,  such  as  carbonic  anhydride.  The  quantity 
of  the  latter  may  be  augmented  many  times  by  work.  But  it 
is  no  longer  believed  that  the  severest  labor  appreciably  in- 
creases the  secretion  of  urea. 

The  division  of  foods  into  heat-producers  and  tissue-builders 
is  unjustifiable,  as  will  appear  from  what  has  just  been  stated, 
as  well  as  from  such  facts  as  the  production  of  fat  from  proteid 
food,  thus  ahowing  that  the  latter  is  indirectly  a  producer  of 
carbonic  anhydride,  assuming  that  fat  is  oxidized  into  that 
substance. 

Animal  Heat. 

Though  a  large  part  of  the  heat  generated  within  the  body 
is  traceable  to  oxidations  taking  place  in  the  tissues,  it  is  better 
to  speak  of  the  heat  as  being  the  outcome  of  all  the  chemical 
processes  of  the  organism ;  and  though  heat  may  be  rendered 
lat«nt  in  certain  organs  for  a  time,  in  the  end  it  must  reappear. 
While  all  the  tissues  are  heat-producers  (thermogenic),  the  ex- 


J 


I 


462 


ANIMAL  PHTSIOLOQT. 


V 


tent  to  which  they  are  such  would  depend,  we  should  suppose, 
upon  the  degree  to  which  they  were  the  seat  of  metabolic  pro- 
cesses ;  and  actual  tests  establish  this  fact.  Thus,  among  glands 
the  liver  is  the  greatest  heat-producer ;  hence  the  blood  from 
this  organ  is  the  warmest  of  the  whole  body.  The  muscles  also 
are  especially  the  thermogenic  tissue. 

The  temperature  of  the  blood  in  the  hepatic  vein  is  warmer 
than  that  in  the  portal,  a  clear  evidence  that  the  metabolism  of 
this  organ  has  elevated  the  temperature  of  the  blood  flowing 
through  it. 

The  temperature  of  the  blood  (its  own  metabolism  being 
slight)  is  a  pretty  fair  indication  of  the  resultant  effect  of  the 
production  and  the  loss  of  heat. 

For  obvious  reasons,  the  temperature  of  different  parts  of 
the  body  of  man  and  other  animals  varies. 

The  statements  of  observers  in  regard  to  the  temperature  of 
various  animals  and  of  different  parts  of  the  body  disagree  in  a 
way  that  \^ould  be  puzzling,  were  it  not  known  how  difficult  it 
is  to  procure  perfectly  accurate  thermometers,  not  to  mention 
individual  differences.  The  axillary  temperature  is  about 
37*5**  C. ;  that  of  the  mouth  a  little  higher,  and  of  the  rectum  or 
vagina  slightly  more  elevated.  The  mean  temperature  of  the 
blood  is  placed  at  39°  C. 

It  is  a  very  striking  fact,  however,  that  the  different  parts 
of  the  body  ordinarily  accessible  by  a  thermometer  vary  so 
little — not  more  perhaps  thftn  a  degree  or  a  degree  and  a  half. 
The  temperature  of  the  hepatic  vein  has  been  put  down  as  39*7°, 
and  it  contains  the  warmest  blood  of  the  body. 

OompanliTe. — ^The  tem])erature  of  various  groups  of  animals 
has  been  stated  to  be  as  follows:  Gull,  37*8°;  swallow,  44*03°; 
dolphin,  35*5°;  mouse,  41*1°;  snakes,  10°  to  12°,  but  higher  in  large 
specimens  (python).  Cold-blooded  animals  have  a  temperature 
a  little  higher  (less  than  1°  0.  nvoally)  than  the  surrounding  air. 
During  the  swarming  of  be^  the  hive  temperature  may  rise 
from  32°  to  40°.  All  cold-blooded  animals  have  probably  a 
higher  temperature  in  the  breeding-season.  In  our  domestic 
mammals  the  normal  temperature  is  not  widely  different  from 
that  of  man. 

Variations  in  the  (werage  temperature  are  dependent  on 
numerous  causes  which  may  affect  either  the  heat  induc- 
tion or  heat  loss :  1.  Change  of  climate  has  a  very  slight  but 
real  influence,  the  temperature  being  elevated  a  fraction  ^f 
a  degree  when  an  individual  travels  from  tilie  poles  toward 


amfitrnKtmiiem 


(i<BtrtXWr^wiw*W'*«e»iw»'--^yj 


d  suppose, 
abolic  pro- 
ang  glands 
blood  from 

uscles  also 

is  warmer 

abolism  of 

od  flowing 

1 

lism  being 
lect  of  the       ; 

• 

at  parts  of 

peratureof 

sagreem  a 
difficult  it 

to  mention 

a  is  about 

)  rectum  or 

' 

kure  of  the 

»rent  parts 

er  vary  so 
and  a  half. 

wrnas39-7°. 

of  animals 

ow,  44-03°; 

ler  in  large 

sinperature 
unding  air. 

re  may  rise 
probably  a 
ir  domestic 

erent  from 

)end^it  on 

at  fKKiduc- 

slight  but 

fraction  ^f 

ties  towiurd 

THE  METABOLISM  OF  THE  BODY. 


463 


the  equator,  and  the  same  may  be  said  of  the  effect  of  the 
temperature  of  a  warm  summer  day  as  compared  with  a  cold 
winter  one.  The  wonder  is  that,  considering  the  external 
temperature,  the  variation  is  so  light.  2.  Starvation  lowers 
the  temperature,  and  the  ingestion  of  food  raises  it  slightly, 
the  latter  increasing,  the  former  decreasing,  the  rate  of  the 
metabolic  processes.  3.  Age  has  its  influence,  the  very  young 
and  the  very  old,  in  whom  metabolism  (oxidation)  is  feeble, 
having  a  lower  temperature.  This  especially  applies  to  the 
newly-born,  both  among  mankind  and  the  lower  mammals; 
and,  as  might  be  supposed,  the  temperature  falls  during 
sleep,  when  all  the  vital  activities  are  diminished.  The  same 
remark  applies  with  greater  force  to  the  hibernating  state 
of  animals.  4.  Very  interesting  are  the  fluctuations  of  tem- 
perature  occurring  daily,  as  shown  by  the  curves  of  Fig. 


KS*. 


Pio.  8«>.-VarlatioiM  of  tbeJMj  ttmpentan  tn  heitlth  durimr  M  boon:  L.,  after  Lieber- 
meiiter ;  J.,  after  JOiseiiMii  (from  Ludois).  "«ubi« 


340.  It  will  be  noticed  that  the  period  of  greatest  bodily 
warmth  is  between  about  four  and  seven  o'clock  in  the  after- 
noon and  the  minimum  temperature  between  two  and  five  in 
the  morning. 

ut  will  be  inferred,  from  the  facts  and  figures  already  cited, 
that  different  kinds  of  food  have  considerably  different  capacity 
for  heat  production.  The  following  estimates  will  still  further 
tend  to  illustrate  this: 

Animal  diet  produces 8,779,634  heat-units 

Food  free  from  nitrogen 2,069,600     "       '* 

Mixeddiet 2,200,200     "       " 

Absenceof  food,  the  heat  amoimts  to..  2,012,816     "       " 
ftt  is  well  known  that  a  m<ui  when  working  not  only 
feels  warmer,  but  actually  produces  more  heat.     The  fol- 
lowing figures  will  give  (approximately)  some  definite  in- 


i  '■•xtm;.'im.'-Mlaii!!Uiimtr!i><i..miu>Lj.um.t)iifii 


mmmmmmmimmmm 


464 


ANIMAL  PHYSIOLOGY. 


formation  on  this  subject,  the  numbers  denoting  the  heat- 
units  produced : 


BESTING    DAY. 

BMt,  le  hours.         Sleep,  8  houn. 
2470-4  820 


Total, 


2790-4 


Beat,  8  hn. 
1285-2 


WORKING  DAT. 

Work,  8  tar*. 

216-90 


Sleep,  8  hn. 
820 


Total, 


3724-8' 


It  appears  from  a  multitude  of  considerations  that  the  body 
is  like  a  steam-engine,  producing  heat  and  doing  work ;  but  it 
is  found  that  while  a  very  good  steam-engine,  as  a  result  of  the 
chemical  processes  going  on  within  it,  converts  \  of  the  poten- 
tial energy  of  its  supplies  into  mechanical  work,  the  other  | 
appearing  as  heat,  the  body  produces  ^  as  work  and  .f  as  heat, 
from  its  income  of  food  and  oxygen. 

While  it  is  perfectly  clear  that  it  is  in  the  metabolic  pro- 
cesses of  the  body  that  we  must  seek  for  the  final  cause  of  the 
heat  produced,  it  is  incumbent  on  the  physiologist  to  explain 
the  remarkable  fact  that  the  mammalian  body  maintains, 
under  a  changing  external  temperature  and  other  climatic 
conditions,  and  with  a  varying  diet,  during  rest  and  labor,  a 
•  temperature  varying  within,  usually,  no  more  than  a  fraction 
of  a  degree  centigrade.    This  we  shall  now  endeavor  to  explain 

in  part. 

(Tlie  Eegnlatioii  of  Ttrnperatore. — It  is  manifest  from  the  facts 
adduced  that  so  long  as  life  lasts  heat  is  being  of  necessity  con- 
stantly produced.    If  there  were  no  provision  for  getting  rid  of 
a  portion  of  this  heat,  it  is  plain  that  the  body  would  soon  be 
consumed  as  effectually  as  if  it  were  placed  in  a  furnace.    We 
observe,  however,  that  heat  is  being  constantly  lost  by  the 
breath,  by  perspiration  (insensible),  by  conduction  and  radia- 
tion from  the  surface  of  the  body,  and  periodically  by  the 
urine  and  fseces.    We  have  seen  that,  while  heat  is  being  pro- 
duced in  all  the  tissues  and  organs  of  the  body,  some  are  es- 
pecially thermogenic,  as  the  glands  and  muscles.    The  skin 
presents  an  extensive  surface,  abundantly  supplied  with  blood- 
vessels, which  when  dilated  may  receive  a  large  quantity  of 
blood,  and  when  contracted  may  necessitate  a  much  larger  in- 
ternal supply,  in  the  splanchnic  region  especially.    It  is  a  mat- 
ter of  common  observation  that,  when  an  individual  exercises, 
the  skin  becomes  flushed,  and  so  with  the  increased  production 
of  heat,  especially  in  the  muscles  (see  page  195),  there  is  a  pro- 
vision for  unusual  escape  of  the  surplus;  at  the  same  time 
sweat  breaks  out  visibly,  or  if  not,  the  insensible  perspiration 


I 


*Wmw*i  ifJmijiiiii-miWiMiiiiN 


iiWjl>  ii»iiiMWiiwniiHni'i|i(iiTi"-nri"i'"^^'f'"' 


■9S-9- 


THE  METABOLISM  OF  THE  BOOT. 


465 


the  heat- 


glerp,  8  hn. 


k  the  body 
irk ;  but  it 
suit  of  the 
the  poten- 
he  other  I 
I  as  heat, 

abolic  pro- 
ause  of  the 

to  explain 
maintains, 
jr  climatic 
nd  labor,  a 

a  fraction 
r  to  explain 

m  the  facts 
cessity  con- 
tting  rid  of 
aid  soon  be 
mace.    We 
lost  by  the 
and  radia- 
ally  by  the 
i  being  pro- 
)me  are  es- 
,    The  skin 
with  blood- 
qnantity  of 
h  larger  in- 
It  is  a  mat- 
al  exercises, 
production 
ere  is  a  pro- 
same  time 
perspiration 


is  generally  increased ;  and  this  accounts  for  an  additional  in- 
crement of  loss ;  while  the  lungs  do  extra  work  and  exhale  an 
increased  quantity  of  aqueous  vapor,  so  that  in  these  various 
ways  the  body  is  cooled.  Manifestly  there  is  some  sort  of  co- 
ordination between  the  processes  of  heat  production  and  heat 
expenditure.  ^The  vaso-motor,  secretory,  and  respiratory  func- 
tions are  modified.  Even  if  an  individual  do  no  work  at  all,  as 
when  in  a  Turkish  bath,  it  becomes  evident,  to  one  submitting 
to  the  experiment  (for  such  it  is  or  may  become),  that  the 
pulse  and  respirations  are  quickened  and  that  there  is  copious 
secretion  of  sweat  following  on  reddening  of  the  skin,  owing 
to  vascular  dilatation.  Exact  quantitative  estimation  of  the 
heat  produced,  as  seen  above,  and  of  the  oxygen  used,  the  car- 
bonic anhydride  and  watery  vapor  exhaled,  shows  that  the 
organs  of  which  we  are  speaking  are  not  only  apparently  but 
actually  doing  more  work.  .  It  is  usual  to  quote  the  case  of 
Drs.  Fordyce  and  Blagdon,  who  learned  to  endure  without 
injury  a  heat  of  137°  C.  (260°  F.),  to  illustrate  the  great  adap- 
tability of  our  own  organism  in  this  respect  We  may  suppose 
that  the  various  co-ordinations  effected,  chiefly  at  all  events 
through  the  central  nervous  system,  and  not  by  the  direct  ac- 
tion of  Hie  heat  upon  local  nervous  mechanisms,  or  the  tissues 
themselves  directly,  are  reflexea 

(i%e  production  of  Tiedt,  however,  seems  to  be  equally  under 
the  influence  of  the  nervous  system,  though  we  know  less  about 
the  details  of  the  matter. 

A  cold-blooded  animal  differs  from  a  warm-blooded  one  in 
that  its  temperature  varies  with  the  surrounding  medium  more; 
hence  the  terms  poikilothermer  and  homoiolhertner  for  cold- 
blooded and  warm-blooded,  would  be  appropriate. 

Such  an  animal,  as  a  frog  or  turtle,  may  have  its  chemical 
processes  slowed  or  quickened,  almost  like  those  going  on  in  a 
test-tube  or  crucible,  by  altering  the  temperature.  Very  different 
is  it,  as  we  have  seen,  in  the  normal  stats  Qf  the  animal  with 
any  mammal  Hence  hibernation  or  an  allied  state  has  become 
a  necessary  protection  for  poDdlothermers,  otherwise  they 
would  perish  outright,  and  the  groups  become  extinct  in  north- 
em  latitudes.  Now,  whmi  a  mammal  is  poisoned  with  curare, 
it  becomes  like  a  poikilothermer.  Like  the  latter,  under  in- 
crease of  temperature,  it  too  uses  more  oxygen  and  produces 
more  carbonic  anhydride.  When  certain  parts  of  the  brain 
are  divided  or  punctured,  a  fall,  similar  to  that  observable 
when  curare  is  given,  is  observable, 
so 


\- 


m 


■mmmMML 


: 


i 


466 


ANIMAL  PHYSIOLOGY. 


It  is  plain  that  vaso-motor  changes  alone  can  not  explain 
these  effects ;  and,  though  possibly  a  part  of  the  rise  of  tem- 
perature, following  exposure  of  the  naked  body  in  a  cool  air, 
may  be  accounted  for  by  the  increased  metabolism  of  internal 
organs,  accompanying  the  influx  of  blood  caused  by  constric- 
tion of  the  cutaneous  capillaries,  it  is  probable  that  in  this  as 
in  so  many  other  instances  the  blood  and  circulation  have  been 
credited  with  too  much,  and  the  direct  influence  of  the  nervous 
system  on  nutrition  and  heat  production  overlooked  or  under- 
estimated. The  thermogenic  center  has  not  yet  been  definitely 
located,  though  some  recent  investigations  seem  to  favor  a  spot 
in  or  near  the  corpus  striatum  for  certain  mammals.  Some  in- 
vestigators also  recognize  a  cortical  heat-center.  It  has  been 
suggested  that  we  may  to  advantage  speak  of  a  thermotoxic 
(regulative  of  loss)  and  a  thermogenic  mechanism  (regulative 
of  production),  and  even  a  tJiermolytic  or  discharging  mechan- 
ism. It  has  been  further  suggested  that  different  nerve-fibers 
may  be  concerned  in  the  actual  work  of  conveying  the  different 
impulses  of  these  respective  mechanisms  to  the  tissues ;  and  the 
whole  theory  has  been  framed  in  accordance  with  the  prevalent 
conception  of  metabolism  as  consisting  of  anabolism  and  ca- 
tabolism,  or  constructive  and  destructive  processes.  But  these 
theories  have  not  yet  been  confirmed  by  experiments  on  ani- 
mals, though  they  are,  in  the  opinion  of  their  authors,  in  har- 
mony with  the  facts  of  fever.  Certainly,  any  theory  that  will 
imply  that  vital  processes  are  more  under  the  control  of  the 
nervous  system  than  has  hitherto  been  taught,  will,  we  think, 
advance  physiology,  as  will  shortly  appear  from  our  own  dis- 
cussion of  the  influence  of  the  nervous  system  on  the  various 
metabolic  processes  generally. 

The  phenomena  observable  in  an  animal  gradually  freezing 
to  death  point  strongly  to  the  direct  influence  of  the  nervous 
system  on  the  production  as  well  as  the  regulation  of  heat. 
The  circulation  must  of  course  be  largely  concerned,  but  it  ap- 
pears as  though  the  nervous  system  refused  to  act  when  the 
temperature  falls  below  a  certain  point.  A  low  temperature 
favors  hibernation,  in  which  we  believe  the  nervous  system 
plays  the  chief  part,  though  the  temperature  in  itself  is  not  the 
determining  cause,  as  we  have  ourselves  proved.  The  fact  that 
the  whole  metabolism  of  a  hibernating  animal  is  lowered,  that 
^Sth  this  there  is  loss  of  consciousness  much  more  profound 
that  in  ordinary  sleep,  of  itself  seems  to  indicate  that  the  nerv- 
ous system  is  at  the  bottom  of  the  whole  matter. 


'HWII  (1*UW(MU1««M 


.injmmMiwmm 


ilWK'  :-HfH^TraiT.a 


THE  METABOLISM  OF  THE  BODY. 


467 


)t  explain 
le  of  tem- 
i  cool  air, 
I  internal 
f  constric- 
in  this  as 
have  been 
le  nervous 
I  or  under- 
i  definitely 
tvor  a  spot 

Some  in- 
:t  has  been 
hermotoxic 
[regulative 
Lg  mechan- 
lerve-fibers 
le  different 
98 ;  and  the 
e  prevalent 
3m  and  ca- 

But  these 
^nts  on  ani« 
ors,  in  har- 
ry that  will 
itrol  of  the 
1,  we  think, 
ur  own  dis- 
the  various 

lly  freezing 
he  nervous 
on  of  heat. 
,  but  it  ap- 
st  when  the 
emperature 
ouB  system 
f  is  not  the 
he  fact  that 
>wered,  that 
re  prof  oimd 
bt  the  nerv- 


PatkftkfiflaL  —  It  is  found  that  many  drugs  and  poisons 
lower  temperatun*,  acting  in  a  variety  of  ways.  In  certain  dis- 
eases, as  cholera,  the  temperature  may  sink  to  23°  G.  in  extreme 
casea  In^fore  death  supervenes.  When  the  temperature  of  the 
blood  i.s  raised  6°  C.  (as  in  sunstroke, etc.), death  occurs;  and  it 
is  well  known  that  prolonged  high  temperature  leads  to  fatty 
degeneration  of  the  tissues  generally.  All  the  evidence  goes  to 
show  that  in  fever  both  the  heat  production  and  the  heat  ex- 
penditure are  interfered  with ;  or,  at  least,  if  not  always,  that 
there  may  be  in  certain  cases  such  a  double  disturbance.  In 
fever  excessive  consumption  of  oxygen  and  production  of  car- 
bon dioxide  occur,  the  metabolism  is  quickened,  hence  its  wast- 
ing (consuming)  effects ;  the  rapid  respiration  tends  to  increase 
the  thirst,  from  the  extra  amount  of  aqueous  vapor  exhaled. 
The  body  is  actually  warmest  during  the  "  cold  stage  "  of  ague, 
when  the  vessels  of  the  skin  are  constricted  and  the  patient 
feels  cold,  because  the  internal  metabolism  is  heightened ;  while 
the  "  sweating  stage  "  is  marked  by  a  natural  fall  of  tempera- 
ture. The  fact  that  the  skin  may  be  dry  and  pale  in  fever 
shows  that  the  thermotoxic  nervous  mechanism  is  at  fault ;  but 
the  chemical  facts  cited  above  (excess  of  GO*,  etc.)  indicate  that 
the  thermogenic  mechanism  is  also  deranged. 


Special  Gonsidbrations. 


(? 


If  the  student  wiU  now  read  afresh  what  has  been  written 
under  the  above  heading  in  relation  to  the  subject  of  digestion,  it 
will  probably  appear  in  a  new  light.  We  endeavored  to  show 
that,  according  to  that  general  principle  of  correlation  which 
holds  throughout  the  entire  organism,  and  in  harmony  with 
certain  facts,  we  were  bound  to  believe  that  digestion  and  as- 
similation, or,  to  speak  in  other  terms,  the  metabolic  processes 
of  the  various  tissues,  in  a  somewhat  restricted  sense,  were 
closely  related.  Beneath  the  common  observation  that "  diges- 
tion waits  on  appetite "  lies  the  deeper  truth  that  food  is  not 
prepared  in  the  alimentary  canal  (digested)  without  some  rela- 
tion to  the  needs  of  the  system  generally.  In  other  words,  the 
voice  of  the  tissues  elsewhere  is  heard  in  the  councils  of  the 
digestive  track,  and  is  regarded ;  and  this  is  effected  chiefly 
through  the  nervous  system.  Qlnttony  may  lead  to  vomiting 
or  diarrhoea — plain  ways  of  getting  rid  of  what  can  not  be 
digested.  But  how  is  it  that  a  hungry  man  who  has  been  with- 
out food  for  twenty-four  hours  can  digest  with  ease  a  quantity 


/I 


II 


si-' 


408 


ANiMAL  PHYSIOLOGY. 


of  food,  ^akeii  at  one  meal,  that  would  otherwise  lead  to  the 
above-not  d  attempts  at  its  removal  ?  It  is  a  mistake  to  ex- 
plain the  result  with  reference  to  the  alimentary  tract  alone. 
The  entire  metabolism  of  the  body  has  a  voice  in  the  matter. 
From  this  point  of  view,  the  benefit  of  abstinence  from  spe- 
cific articles  of  diet,  partial  or  complete,  of  taking  at  times 
very  light  meals,  and  much  more  that  experience  warrants, 
receives  an  explanation.  Too  little  attention  seems  to  have 
been  given  to  this  aspect  of  the  subject  that  we  are  now  en- 
deayoring  to  present  briefly. 

(Until  the  nature  of  metabolism  is  more  completely  under- 
stood, it  will  be  impossible  to  treat  the  subject  of  diet,  either 
in  hc^th  or  disease,  with  such  confidence  as  to  enable  us  to 
prescribe  upon  scientific  principles  alone.  Very  much  must 
still  be  empirical,  the  outcome  of  trial  and  result,  which  is, 
however,  after  all,  experiment  in  a  crude  form ;  and  individxial 
peculiarities  that  are  inscrutable  in  their  nature  will  always  be 
encountered.  Notvrithstanding,  if  physicians  will  avail  them- 
selves of  the  best  that  is  known  in  the  realm  of  physiologi- 
cal dietetics,  and  then  contribute  the  results  of  their  observa- 
tions in  accurate  form,  substantial  progress  will  be  made  in 
due  time. 

lTobitl0iL-^Ve  have  already  alluded  to  some  of  those  modi- 
fications in  the  form  of  the  digestive  organs  that  indicate  an 
unexpected  plasticity,  and  impress  the  fact  of  the  close  rela- 
tion of  form  and  function.  The  conversion  of  a  sea-gull  into  a 
graminivorous  bird,  with  a  corresponding  alteration  in  the  na- 
ture of  the  form  of  the  stomach  (it  becoming  a  gizzard),  with 
doubtless  modifications  in  the  digestive  processes,  when  re- 
garded more  closely,  implies  coadaptations  of  a  very  varied 
kind.  These  are  as  yet  but  imperfectly  known  or  understood, 
and  the  subject  is  a  wide  and  inviting  field  for  the  physiolo- 
gist. Darwin  and  others  have  indicated,  though  but  imper- 
fectly, some  of  the  changes  that  are  to  be  regarded  in  animals 
as  correlations ;  but  in  physiology  the  subject  has  received  but 
little  attention  as  yet.  We  have  in  several  parts  of  this  work 
called  attention  to  it;  but  the  limits  of  space  prevent  us  dmag 
little  more  than  attempting  to  widen  the  student's  field  of 
vision  by  introducing  such  considerations.  The  influence  of 
climate  on  metabolism,  an  undoubted  fact,  has  many  implica- 
tions. 

/Any  one  who  keeps  a  few  wild  animals  in  confinement  un- 
dei>  close  observation,  and  endeavors  to  ascertain  how  their 


'wiaiwgwg!iiiL'iijimiiiiiBtgi.'..a!iiui!i 


THE  METABOLISM  OF  THE  BODY. 


460 


Eld  to  the 
kke  to  ex- 
act alone, 
le  matter, 
from  spe- 
;  at  times 
warrants, 
B  to  have 
e  now  en- 

ely  under- 
iiet,  either 
able  us  to 
inch  must 
,  which  is, 
individual 
I  always  be 
vail  them- 
physiologi- 
ir  observa- 
ye  made  in 

ihose  modi- 
indicate  an 

close  rela- 
-guU  into  a 
a  in  the  n«- 
a»rd),  with 
when  re- 
rery  varied 
understood, 
e  physiolo- 
but  imper- 

in  animals 
'eceived  but 
if  this  work 
tnt  us  d(HBg 
it's  field  of 
influence  of 
huy  implica- 

Aement  un- 
how  their 


natural,  self-chosen  diet  may  be  varied  when  confined,  will 
be  astonished  at  the  plasticity  of  their  instincts,  usually  con- 
sidered as  so  rigid  in  regard  to  feeding.  These  facts  help 
one  to  understand  how  by  the  law  of  habit  and  heredity 
each  group  of  animals  has  come  to  prefer  and  flourish  best 
upon  a  certain  diet.  But  habit  itself  implies  an  original 
deviation  some  time,  in  which  is  involved,  again,  plasticity 
of  nature  and  power  to  adapt  as  well  as  to  organize.  With- 
out this,  evolution  of  function  is  incomprehensible ;  but  with 
this  principle,  and  the  tendency  for  what  has  once  been  done 
to  be  easier  of  repetition ;  and,  finally,  to  become  organized, 
a  flood  of  light  is  thrown  upon  the  subject  of  diet,  diges- 
tion, and  metabolism  generally.  On  these  principles  it  is 
possible  to  understand  those  race  differences,  even  individ- 
ual differences,  which  as  facts  must  be  patent  to  all  observ- 
ers. Every  individual's  ovm  history  will  teach  him  that  he 
can  learn  to  digest  and  assimilate  what  was  once  all  but  a 
poison  to  his  organism;  so  that  it  becomes  comprehensible 
how  a  Chinaman,  for  example,  can,  not  only  remain  in  health,\ 
but  do  a  large  amount  of  work  daily  on  a  diet  on  which  the 
ordinary  Englishman  might  well-nigh  starve  before  he  could 
adapt  himself  to  it. 

(R  is  also  a  well-established  fact  that  whole  families  crave 
and  seem  to  require  certain  articles  of  diet  in  excess,  as  com- 
pared with  the  majority — e.  g.,  a  meat  diet.  In  some  in- 
stances, at  all  events,  this  can  be  traced  to  pathological  excess 
in  the  ancestors.  It  is  important  to  recognize,  however,  that 
while  such  a^Bet  upon  the  whole  may  be  the  best  that  can  be 
appropriated  at  the  time,  it  is  associated  with  certain  aberrations 
of  function  which  it  is  desirable  to  correct;  hence  the  wisdom 
of  withholding  from  such  people,  even  children,  to  a  certain 
extent,  the  meai  which  they  so  much  crave.  The  habit  of  the 
metabolism  mS^Tbi 'modified.  The  rapid  rate  of  speed  of  the 
metabolic  processes,  which  an  excess  of  such  a  diet  is  apt  to 
beget,  leads  to  various  bad  results,  such  as  great  irritability  of 
the  nervous  system,  and  a  general  lack  61  stability  and  equi- 
po^tt^he  vital  machtne.^^" 

le  principle  of  natural  selection  has  clearly  played  a  great 
in  determining  the  diet  of  a  species;  the  surviving  emi- 
grants to  a  new  district  must  be  those  that  can  adapt  to  the  local 
environment  best,  including  the  food  which  the  region  supplies. 
The  greater  capability  of  resisting  hunger  and  thirst  in  some 
iudividuals  of  a  species  implies  great  differences  in  the  meta- 


470 


ANIMAL  PHTSIOLOGT. 


bolic  processes,  though  these  are  mostly  unknown  to  us ;  and 
the  same  remark  applies  to  heat  and  cold. 

It  seems  clear  that  hibernation  is  an  acquired  habit  of  the 
whole  metabolism,  with  great  changes  in  the  functional  condi- 
tion of  the  nervous  system  recurring  periodicaUy,  and,  in  fact, 
dependent  on  these,  by  which  certain  large  divisions,  as  the 
reptiles,  amphibianii,  and  certain  mammals  among  vertebrates, 
are  enabled  to  escape  individual  death  and  extinction  as  groups. 
We  may  suppose  that,  for  example,  among  invertebrates,  by  a 
process  of  natural  selection,  those  survived  that  could  thus 
adapt  themselves  to  the  environment;  while,  among  mammals, 
hibernation  may  be  considered  as  a  process  of  reversion,  per- 
haps, for  the  homoiothermer  becomes  very  much  a  poikilo- 
thermer  during  hibernation,  the  latt«r  again  reverting  to  a 
condition  existing  in  lower  forms,  and  not  wholly  unlike  that 
of  plants  in  winter.  This  can  be  understood  on  the  princi- 
ple of  the  origin  of  higher  from  lower  forms;  otherwise  it 
is  difficult  to  understand  why  similar  states  of  the  metabolism 
should  prevail  in  groups  widely  separated  in  form  and  func- 
tion. If  all  higher  groups  bear  a  derivative  relation  to  the 
lower,  what  is  common  in  their  nature,  as  we  usually  find 
them,  as  well  as  the  peculiar  resemblances  of  the  metabolism 
of  higher  to  lower  forms  in  sleep,  hibernation,  etc.,  can  be 
imderstood  in  the  light  of  physiological  reversion. 

The  origin  of  a  homoiothermic  (warm-blooded)  condition 
itself  is  to  be  sought  for  in  the  principle  of  natural  selection. 
It  was  open  to  certain  organisms,  we  may  assume,  either  to 
adapt  to  a  temperature  much  below  that  of  their  blood,  or  to 
hibernate;  failing  to  make  either  adaptation  would  result  in 
death ;  and  gradually,  no  doubt,  involving  the  death  of  num- 
berless individuals  or  species,  the  resisting  power  attained  the 
marvelous  degree  that  we  are  constantly  witnessing  in  all 
homoiothermers. 

The  daily  variations  of  the  bodily  temperature  in  homoio- 
thermers is  a  beautiful  example  of  the  law  of  rhythm  evident 
in  the  metabolism.  Hibernation  is  another  such.  While  these 
are  cleur  cases,  it  is  without  doubt  true  that,  did  we  but  know 
more  of  the  subject,  a  host  of  exampleB  of  the  operation  of  this 
law  might  be  instanced. 

We  can  but  touch  on  these  subjects  enough  to  show  that 
they  deserve  an  attention  not  as  yet  bestowed  on  them ;  and  to 
the  thoughtful  it  will  be  evident  that  their  influence  on  prac- 
tical life  might  be  made  very  great  were  they  but  rightly  ap- 


lailriWIUllilKitMl 


0  us;  and 

ibit  of  the 
>nal  condi- 
id,  in  fact, 
ns,  as  tlie 
ertebrates, 
as  groups, 
rates,  by  a 
;ould  thus 
mammals, 
trsion,  per- 
a  poikilo- 
rting  to  a 
inlike  that 
;he  princi* 
herwise  it 
aetabolism 
and  f  uuc- 
ion  to  the 
iually  find 
aetabolism 
tc.,  can  be 

1  condition 
I  selection. 
,  either  to 
•lood,  or  to 
i  result  in 
thof  num* 
stained  the 
ling  in  all 

in  homoio- 
im  evident 
Vhile  these 
)but  know 
tion  of  this 


I  show  that 
em ;  and  to 
}e  on  prao- 
rightly  ap* 


iiwUft-wwiaBW 


THE  HETABOUSM  OF  THE  BODY. 


471 


prehended.  In  that  preventive  medicine  of  the  future  to  which 
we  fondly  look  to  advance  the  welfare  of  mankind,  such  consid-i 
orations  must  largely  enter. 

The  Influence  of  the  Nervous  System  on  Metabolism 

(Nutrition). 

This  subject  is  of  the  utmost  importance,  and  has  not  re- 
ceived the  attention  hitherto,  in  works  on  physiology,  to  which 
we  believe  it  is  entitled,  so  that  we  must  discuss  it  at  some 
length. 

^e  may  first  mention  a  number  of  facts  on  which  to  base 
conclusions :  1.  Section  of  the  nerves  of  bones  is  said  to  be  fol- 
lowed by  a  diminution  of  their  constituents,  indicating  an 
alteration  in  their  metabolism.  2.  Section  of  the  nerves  sup- 
plying a  cock's  comb  interferes  with  the  growth  of  that  ap- 
pendage. 3.  Section  of  the  spermatic  nerves  is  followed  by  de- 
generation of  the  testicle.  4.  After  injury  to  a  nerve  or  its 
center  in  the  brain  or  spinal  cord,  certain  affections  of  the 
skin  may  appear  in  regions  corresponding  to  the  distribution 
of  that  nerve :  thus,  herpes  zoster  is  an  eruption  that  follows 
frequently  the  distribution  of  the  intercostal  nerve.  6.  When 
the  motor  cells  of  the  anterior  horn  of  the  spinal  cord  or  cer- 
tain cells  in  the  pons,  medulla,  or  cms  cerebri  are  disordered, 
there  is  a  form  of  muscular  atrophy  which  has  been  termed 
"active,"  inasmuch  as  the  muscle  does  nbt  waste  merely,  but 
the  dwindling  is  accompanied  by  proliferation  of  the  muscle 
nuclei.  6.  In  ocufedectt&i^tiA  bed-sores  form  within  a  few  hours 
or  days  of  the  appearance  of  the  cerebral  or  spinal  lesion,  and 
this  with  every  precaution  to  prevent  pressure  or  the  other 
conditions  that  favor  the  formation  of  such  sores.  7.  After 
section  of  both  vagi,  death  results  after  a  period,  varying  in 
time,  as  do  also  the  symptoms,  with  the  animal.  In  some  ani- 
mals pneumonia  seems  to  account  for  death,  since  it  is  found 
that,  if  this  disease  be  prevented,  life  may,  at  all  events,  be 
greatly  prolonged.  The  pneumonia  has  been  attributed  to 
paralyses  of  the  muscles  of  the  larynx,  together  with  loss  of 
sensibility  of  the  larynx,  trachea,  bronchi,  and  the  lungs,  so 
that  the  glottis  is  not  closed  during  deglutition,  and  the  food, 
finding  its  way  into  the  lungs,  has  excited  the  disease  by  irrita- 
tion. The  possibility  of  vaso-motor  changes  is  not  to  be  over- 
looked. In  birds,  death  may  be  subsequent  to  pneumonia  or 
to  inanition  from  paralysis  of  the  oesophagus,  food  not  being 


-..HMHiWMHWlM 


ITS 


ANIMAL  PHTSIOLOOT. 


swallowed.  It  is  noticed  that  in  these  creatures  there  is  fatty 
(and  sometimes  other)  degeneration  of  the  heart,  liver,  stomach, 
and  muscles.  8.  Section  of  the  trigeminus  nerve  within  the 
skull  has  led  to  disease  of  the  corresponding  eye.  This  opera- 
tion renders  the  whole  eye  insensible,  so  that  the  presence  of 
offending  bodies  is  not  recognized ;  and  it  has  been  both  as- 
serted" and  denied  that  protection  of  the  eye  from  these  pre- 
vents the  destructive  inflammation.  With  the  loss  of  sensi- 
bility there  is  also  vaso-motor  paralysis,  the  intra-ocular  ten- 
sion is  diminished,  and  the  relations  of  the  nutritive  lymph  to 
the  ocular  tissues  are  altered.  But  all  disturbances  of  the  eye 
in  which  there  are  vaso-motor  alterations  are  not  followed  by 
degenerative  changes.  9.  Degeneration  of  the  salivary  glands 
follows  section  of  their  nerves.  10.  After  suture  of  long-di^ 
vided  nerves,  indolent  ulcers  have  been  known  to  heal  with^ 
great  rapidity.  This  last  fact  especially  calls  for  explanation. 
It  will  be  observed,  when  one  comes  to  examine  nearly  all  such 
instances  as  those  referred  to  above,  that  they  are  complex. 
Undoubtedly,  in  such  a  case  as  the  trigeminus  or  the  vagi, 
many  factors  contribute  to  the  destructive  issue ;  but  the  fact 
that  many  symptoms  and  lesions  are  concomitants  does  not,  of 
itself,  negative  the  view  that  there  may  be  lesions  directly 
dependent  on  the  absence  of  the  functional  influence  of  nerve- 
fibers.  We  prefer,  however,  to  discuss  the  subject  on  a  broader 
basis,  and  to  found  opinions  on  a  wider  survey  of  the  facts  of 
ph^ology. 

rAf  ter  a  little  time  (a  few  hours),  when  the  nerves  of  the  sub- 
maxillary gland  have  been  divided,  a  flow  of  saliva  begins  and 
is  continuous  till  the  secreting  cells  become  altered  in  a  way 
visible  by  the  microscope.  Now,  we  have  learned  that  proto- 
plasm can  discharge  all  its  functions  in  the  lowest  forms  of 
.animals  and  in  plants  independently  of  nerves  altogether. 
What,  then,  is  the  explanation  of  this  so-called  "paralytic 
secretion  "  of  saliva  ?  The  evidence  that  the  various  functions 
of  the  body  as  a  whole  are  discharged  as  individual  acts  or 
series  of  acts  correlated  to  other  functions  has  been  abundantly 
shown;  and,  looking  at  the  matter  closely,  it  must  seem  un- 
reasonable to  suppose  that  this  would  be  the  case  if  there  was 
not  a  close  supervision  by  the  nervous  system  over  even  the 
details  of  the  processes.  We  should  ask  that  the  contrary  be 
proved,  rather  than  that  the  burden  of  proof  shotdd  rest  on  the 
other  side.  Let  us  assume  that  such  is  the  case ;  that  the  entire 
behavior  of  every  cell  of  the  body  is  directly  or  indirectly  con> 


rtrfniilii 


mtDHiMifmom 


lattA^dMMMiMMIlM 


THE  METABOLISM  OF  THE  BODY. 


478 


re  is  fatty 
',  8tomacli, 
rithin  the 
his  opera- 
resence  of 
I  both  as- 
these  pre- 
t  of  sensi- 
icular  ten- 
I  lymph  to 
at  the  eye 
Uowed  by 
Biry  glands 
)f  long-di^ 
heal  withj 
:planation. 
ly  all  such 
)  complex, 
the  vagi, 
it  the  fact 
oes  not,  of 
as  directly 
B  of  nerve- 
t  a  broader 
he  facts  of 

of  the  sub- 
begins  and 

in  a  way 
hat  proto- 
it  forms  of 
altogether, 
"paralytic 
i  functions 
aal  acts  or 
abundantly 
;  seem  un- 

there  was 
even  the 
ontrary  be 
rest  on  the 
;  the  entire 
rectly  con- 


trolled by  the  nervous  system  in  the  higher  animals,  especially 
mammals,  and  ask.  What  facts,  if  any,  are  opposed  to  such  a 
view  ?  We  must  suppose  that  a  secretory  cell  is  one  that  has 
been,  in  the  course  of  evolution,  specialized  for  this  end.  What- 
ever may  have  been  the  case  with  protoplasm  in  its  unspecialized 
form,  it  has  been  shown  that  gland-cells  can  secrete  independ- 
ently of  blood-supply  (pages  321,  416)  when  the  nerves  going  to 
the  gland  are  stimulated.  Now,  if  these  nerves  have  learned,  in 
the  course  of  evolution,  to  secrete,  then  in  order  that  they  shall 
remain  natural  (not  degenerate)  they  must  of  necessity  secrete ; 
which  means  that  they  must  be  the  subject  of  a  chain  of  meta- 
bolic processes,  of  which  the  final  link  only  is  the  expulsion  of 
formed  products.  Too  much  attention  was  at  one  time  directed 
to  the  latter.  It  was  forgotten,  or  rather  perhaps  unknown,'^ 
that  the  so-called  secretion  was  only  the  last  of  a  long  series  of/ 
acts  of  the  cell.  True,  when  the  cells  are  left  to  themselves, 
when  no  influences  reach  them  from  the  stimulating  nervous 
centers,  their  metabolism  does  not  at  once  cease.  As  we  view 
it,  they  revert  to  an  original  ancestral  state  when  they  per- 
formed their  work,  lived  their  peculiar  individual  life  as  less 
specialized  forms  wholly  or  partially  independent  of  a  nervous 
system.  But  such  divorced  cells  fail;  they  do  not  produce 
normal  saliva,  their  molecular  condition  goes  wrong  at  once, 
and  this  is  soon  followed  by  departures  visible  by  means  of  the 
microscope.  But  just  as  secretion  is  usually  accompanied  by 
excess  of  blood,  so  most  functional  conditions,  if  not  all,  de- 
mand an  unusual  supply  of  pabulum.  This  is,  however,  no 
more  a  cause  of  the  functional  condition  than  food  is  a  cause 
of  a  man's  working.  It  may  hamper,  if  not  digested  and  assimi- 
lated. It  becomes,  then,  apparent  that  the  essential  for  metab=^ 
olism  is  a  vital  connection  with  the  dominant  nervous  system.'^ 
It  has  been  objected  that  the  nervous  system  has  a  metab- 
olism of  its  own  independent  of  other  regulative  influences; 
but  in  this  objection  it  seems  to  be  forgotten  that  the  nervous 
system  is  itself  made  up  of  parts  which  are  related  as  higher 
and  lower,  or  at  all  events  which  intercommunicate  and  ener- 
gize one  another.  Wo  have  learned  that  one  muscle-cell  hafT^ 
power  to  rouse  another  to  activity  when  an  impulse  has  reached ' 
it  from  a  nervous  center.  Doubtless  this  phenomenon  has 
many  parallels  in  the  body,  and  explains  how  remotely  a  nerv- 
ous center  may  exert  its  power.  It  enables  one  to  understand  to 
some  extent  many  of  those  wonderful  co-ordinations  (obscure 
in  detail)  that  are  constantly  taking  place  in  the  body.    We 


mmi 


iUlH 


mtM 


iiHMIIli 


474 


ANIMAL  PHYSIOLOOy. 


thitik  the  facts  as  they  accumulate  will  more  and  more  show, 
as  has  been  already  urged,  that  the  influence  of  blood-pressure 
on  the  metabolic  (nutritive)  processes  has  been  much  over- 
estimated. They  are  not  essential  but  concomitant  in  the 
highest  animals.  Turning  to  the  case  of  muscle  we  find  that 
when  a  skeletal  muscle  is  tetanized  the  essential  chemical  and 
electrical  phenomena  are  to  be  regarded  as  changes  differing  in 
degree  only  from  those  of  the  so-called  resting  state.  There  is 
more  oxygen  used,  more  carbonic  anhydride  excreted,  etc.  The 
change  in  form  seems  to  be  the  least  important  from  a  physio- 
logical point  of  view.  Now,  while  all  this  can  go  on  in  the 
absence  of  blood  or  even  of  oxygen,  it  can  not  take  place  with- 
out nerve  influence  or  something  simxilating  it.  Cut  the  nerve7 
of  a  muscle,  and  it  undergoes  fatty  degeneration,  and  atrophies.) 
True,  this  may  be  deferred,  but  not  indefinitely,  by  the  applica- 
tion of  electricity,  acting  somewhat  like  a  nerve  itself,  and  in- 
ducing the  approximately  normal  series  of  metabolic  changes. 
If,  then,  the  condition  when  not  in  contraction  (rest)  differs 
from  the  latter  in  all  the  essential  metabolic  changes  in  rate  or 
degree  only;  and  if  the  functional  condition  or  accelerated 
metabolism  is  dependent  on  nerve  influence,  it  seems  reason- 
able to  believe  that  in  the  resting  condition  the  latter  is  not 
withheld. 

Certain  forms  of  paralysis  (e.  g.,  hysterical)  are  not  followed 
by  atrophy.  Why  ?  Because  in  this  form  the  nerve  influence 
is  still  exerted. 

^^he  recent  investigations  on  the  heart  make  such  views  as 
we  are  urging  clearer  stilL  It  is  known  that  section  of  the 
vagi  leads  to  degeneration  of  the  cardiac  structure.  We  now 
know  that  this  nerve  contains  fibers  which  have  a  diverse 
action  on  the  metabolism  of  the  heart,  and  that,  according 
as  the  one  or  the  other  set  is  stimulated,  so  does  the  electri- 
cal condition  vary ;  and  everywhere,  so  far  as  known,  a  differ- 
ence in  electrical  conditions  seems  to  be  associated  with  a 
difference  in  metabolism,  which  may  be  one  of  degree  only, 
perhaps,  in  many  instances — still  a  difference.  The  fiicts  as 
brought  to  light  by  experimental  stimulation  harmonize  with 
the  facts  of  degeneration  of  the  cardiac  tissue  on  section  of  the 
vagi ;  but  this  is  only  clear  on  the  view  we  are  now  presenting, 
that  the  action  of  the  nervous  system  is  not  only  imiversal, 
Cbutthst  it^is  jcqnjrfflwi^^  that  function  is  not  an  isolated  and 
inclipendent  condition  of  an  organ  or  tissue,  but  a  part  of  a 
long  series  of  metabolic  changes.    Il  h  crue  that  one  or  more 


KM 


bhbi 


Qore  show, 
d-pressure 
mch  over- 
mt  in  the 
e  find  that 
3mical  and 
li£fering  in 
,  There  is 
I,  etc.  The 
1  a  physio- 
on  in  the 
alace  with- 
t  the  nerve7 
.  atrophies.] 
lie  applica- 
elf ,  and  in- 
c  changes, 
est)  differs 
3  in  rate  or 
iccelerated 
ms  reason- 
,tter  is  not 

)t  followed 
a  influence 

sh  views  as 
;ion  of  the 
We  now 
a  diverse 
according 
the  electri- 
n,  a  differ- 
ed with  a 
jgree  only, 
le  facts  as 
ionize  with 
tion  of  the 
presenting, 
universal, 
tolated  and 
b  part  of  a 
ne  or  more 


THE  METABOLISM  OF  THE  BODY. 


476 


of  such  changes  may  be  arrested,  just  as  all  of  them  may  go 
on  at  a  less  rate,  if  this  actual  outpouring  of  pancreatic  secre- 
tion is  not  constant ;  but  secretion  is.  not  summed  up  in  dis- 
charge merely ;  and,  on  the  other  hand,  it  would  seem  that  in 
some  animals  the  granules  of  the  digestive  glands  are  being 
renewed  while  they  are  being  used  up,  in  secreting  cells.  The 
processes  may  be  simultaneous  or  successive.  Nor  do  we  wish 
to  imply  that  the  nervous  system  merely  holds  in  check  or  in 
a  very  general  sense  co-ordinates  processes  that  go  on  unorigi- 
nated  by  it.  We  think  the  facts  warrant  the  view  that  they  are 
in  the  highest  mammals  either  directly  (mostly)  or  indirectly 
originated  by  it,  that  they  would  uQtu^ke  place  in  the  absence 
of  this  constant  nervous,  influence.  The  facts^?  common  ob- 
servation, as  well  as  the  facts  of  disease,  point  in  the  strongest 
way  to  such  a  conclusion.  Every  one  has  experienced  the  in- 
fluence, on  not  one  but  many  functions  of  the  body,  we  might 
say  the  entire  metabolism,  of^  depressing  or  exalting  emotions. 
The  failure  of  appetite  and  loss  of  flesh  and  mental  power  under 
thelnfluence  ot  gnet  or  worry,  tell  a  plain  story.  Such  broad 
facts  afeoFmfinitely  more  value  in  settling  such  a  question  as 
that  now  discussed  than  any  single  experiment.  The  best  test 
of  any  theory  is  the  extent  to  which  it  will  explain  the  whole 
round  of  facts.  Take  another  instance  of  the  influence  over 
me^bolism  of  the  nervous  system. 

(^very  athlete  knows  that  he  may  overtrain — i.  e.,  he  may 
use  his  muscles  so  much  as  to  disturb  the  balance  of  his  powers 
somewhere— very  frequently  his  digestion;  but  often  there 
seems  to  be  a  general  break — ^the  whole  metabolism  of  the  body 
seems  to  be  out  of  gear.  JfjivBassume  a  constiuit  nervous  influ- 
ence over  the  metabolic  processes,  this  is  comprehensible.  The 
^enteii  can  produce  only  so  mu^  of  what  we  may  call  nerv- 
ous force,  using  the  term  in  the  sense  of  directive  power ;  and 
if  this  be  unduly  diverted  to  the  muscles,  other  parts  must 
suffer.  (The  same  holds  of^exoesdve  mental  jBj)pLics>tjon^ 

(On  this  view  also^e  value  of  rest  or  change  of  occupation 
becos)^fie_clMrr  The  nervdtn  centers  are  not  without  some  r»-< 
semblance  to  a  battery ;  at  most,  the  latter  can  generate  only  a( 
definite  quantity  of  electricity,  and,  if  a  portion  of  this  be  di- / 
verted  along  one  conductor,  less  must  remain  to  pass  by  anyi 
other. 

rlt  is  of  practical  importance  to  recognize  that  under  great 
excitement  unusual  discharges  from  a  nerve-center  may  lead 
to  unwonted  f imctional  activity :  thus,  under  the  stimulus  of 


tmmsa 


476 


ANIMAL  PHTSIOLOOY. 


:•« 


the  occasion  a  man  may  in  a  boat-race  originate  muscular  con- 
tractions that  he  could  not  by  the  strongest  efforts  of  his  will 
call  forth  under  other  .circumstances.  Such  are  always  dan- 
gerous. We  might  speak  of  a  reserve  or  residual  nerve  force, 
the  expenditure  of  which  results  in  serious  disability.  It  als07 
applies  to  mental  and  emotional  effects  as  well  as  muscular,  s 

'  and  seems  to  us  to' throw  light  upon  many  of  the  failures  und^ 

(juctiess^  Xso  called)  of  life.  "      ~  ""^"^ 

(^  iseems  thai  our  past  views  of  secretion  and  nutrition  have 
been  partial  rather  than  erroneous  in  themselves,  and  it  is  a 
question  whether  it  would  not  be  well  to  substitute  some  other 
terms  for  them,  or  at  least  to  recognize  them  more  clearly  as 
phases  of  a  universal  metabolism.  (V^  a^^pear  to  be^^^ 
in^making  a  wider  generalization.  To  regard  processes  con- 
cerned in  building  up  a  tissue  as  i4>art  from  those  that  are  rec- 
ognized as  constituting  its  function,  seems,  with  the  knowledge 
we  at  present  possess,  to  be  illogical  and  unwise.    Whether, 

.  in  the  course  of  evolution,  certain  nerves,  or,  as  seems  more 
likely,  certain  nerve-fibers  in  the  body  of  nerve-trunks,  have 
become  the  medium  of  impulses  that  are  restricted  to  regulat- 
ing certain  phases  of  metabolism — as,  e.  g.,  expulsion  of  formed 
products  in  gland-cells— is  not,  from  a  general  point  of  view, 
improbable,  and  is  a  fitting  subject  for  further  investigation. 
But^it  will  be  seen  that  we  should  regard  all  nerves  as  "tro- 
phic  "  in  the  wider  sense.    M^hai  is  nic«t  needed,  apparently,  is  a^ 
mqrejust  eistimatibn  of  the  relative  parts  played  by  blood  and^ 
Ijlood-prQssure,  i^djhe direct  influence  of  the  nervous  system/ 
on^e  life-work j>f  the  oeUT^  These  views  are  greatly  iatfengQi- 
ened  by  the  facts,  welTlniown  to  every  observer  of  disease  in 
the  human  subject.    The  preponderating  development  of  the 

(cerebrun|/in  man  must  be  taken  into  account  in  the  working 
of  every  organ.    ToJiaye  a^erithjr  jtomewh,  Uyer^^lrid^^ 
j!tc.^is  not jBnough ;  for  ,r«Oi£a]|hjJ^l  the  parts  of  that  great 
complex  of  or^^s  we  call  the  brain  must  not  only  work,Jbut, 
V^i  in  concert. 

.  ^^e  must  regard  the  ^rvous  centeriMas  the  source  of  cease- 
less pulses  that  operate  upon~air  parts,  originating  and  con- 
trolling the  entire  metabolism,  of  which  what  we  term  func- 
tions are  but  certain  phases,  parts  of  a  whole,  but  essential  for 
the  health  or  normal  condition  of  the  tissues.  Ag^nst^uskjl 
.view  ire^now  no  fiicts,  eith9r-«f  the  he^  or  disordered  orj- 
ganism. 

IvBuurj  of  MttaboHi  I— -Very  briefly,  and  somewhat  incom- 


(. 


■liMI  ,1  lull  iiiiii  <"• 


scular  con- 
of  his  will 
Iways  dan- 
aerve  force, 
ity.  It  als07 
i  muscular,  s 
allures  and^ 

britiou  have 
and  it  is  a 
some  other 
e  clearly  as 
B  warranted 
ocesses  con- 
ihat  are  rec- 
I  knowledge 
Whether, 
seems  more 
runks,  have 
L  to  regidat- 
n  of  formed 
nt  of  view, 
vestigation. 
res  as  *'tro- 
>arently,isa^ 
y  blood  and^ 
70US  system/ 
ly  stfengQi- 
f  disease  in 
nent  of  the 
;he  working 
er^Jridneys, 
f  that  great 
y  work,Jbut, 

rceof  oease- 
ag  and  con- 
)  term  func> 
essential  for 

ainstjBuslL§ 
Isordered  or^ 

what  incom- 


"Tl 


■.U 


THB  METABOLISM  OF  THE  BODY. 


477 


pletely,  we  may  sum  up  the  chief  results  of  our  present  knowl- 
edge (and  ignorance)  as  follows : 

(uHycogen  is  found  in  the  livers  of  all  v  ^-tebrate  and  some 
invertebrate  animals.  The  quantity  varies  with  the  diet,  being 
greatest  with  an  excess  of  carbohydrates. 

It  seems  likely  that  glycogen  is  manufactured  from  the  pro- 
toplasm of  the  liver-cells,  though  it  is  possible  that  the  latter 
may  act  on  substances  contained  in  the  lymph,  and  convert 
them  into  glycogen  which  they  store  up.  The  phenomena  of 
diabetes  meUHua  seem  to  indicate  that  vaso-motor  effects  in  the 
liver  are  not  essential  to  the  formation  of  the  excess  of  sugar 
in  that  disease,  which  excess  is  only  one  symptom,  there  being 
frequently  also  a  largely  increased  secretion  of  urea;  but  inas- 
'■^^^k^ilhe juervous  system  is  greatly  deranged  in  this  malady, 
{EeTsymptoms,  etc.,  of  the  disease  as  a  whole  may  be  rather 
regarded  as  showing  how  important  is  the  due  influence  of 
thepiervous  system. 

(Glycogen  may  be  regarded  as  stored  material  to  be  convert- 
ed into  (feugay,  as  required  by  the  organism ;  though  the  fexact 
useof  the  sugar  and  the  method  of  its  disposal  are(unknown. 

\^a^  is  not  stored  up  in  the  body  as  the  result  of  being 
merely  picked  out  from  the  blood  ready  made ;  but  is  a  genuine 
product  of  the  metabolism  of  the  tissues,  and  may  be  formed 
from  fatty,  carbohydrate,  or  proteid  food.  This  becomes  es- 
pecially clear  when  the  difference  in  the  fat  of  animals  from 
that  on  which  they  feed  is  considered,  as  weU  as  the  direct  re- 
sults of  feeding  experiments,  and  the  nature  of  the  secretion  of 
milk. 

(^e  liver  seems  be  engaged  in  a  very  varied  round  of  meta- 
bofic  processes:  the  manufacture  of  bile,  of  glycogen,  of  urea, 
and  probably  of  many  other  substuices,  some  known  and 
others  unTmown,  as  chemical  individuals.  Urea  is  in  great 
part  probably  only  appropriated  by  the  kidney-cells  (Amoeba- 
like)  from  the  blood  in  which  it  is  found  ready-made;  though 
it  may  be  that  a  part  is  formed  in  these'oells,  either  from 
bodies  some  steps  on  the  way  toward  urea,  or  out  of  their  pro- 
topbasm^m  fsA  seems  to  be  by  the  cells  of  the  mammary  gland. . 

(Jhe  leucin  (and  tyrosin  ?)  of  the  digestive  canal  sustains 
some  relation  to  the  manufacture  of  urea  by  the  liver,  and 
possibly  by  the  spleen  and  other  orgems;  for  an  animal  diet 
increases  these  products,  and  also  the  urea  excreted.  Creatin, 
one  of  the  products  of  proteid  metabolism,  and  possibly  allied 
bodies,  may  be  oonsidered  as  in  a  certain  sense  antecedents  of 


i*  ■ 


•r 


478 


ANIMAL  PHTSIOLOOT. 


urea :  uric  acid,  however,  does  not  seem  to  be  such,  nor  is  it  to 
be  regarded  as  a  body  that  has  some  of  it  escaped  complete 
oxidation,  but  rather  as  a  result  of  a  distinct  departure  of  the 
metabolism ;  and  there  are  facts  which  seem  to  indicate  that 
the  uric-acid  metabolism  is  the  older,  frora  an  evolutionary 
point  of  view,  and  that  in  mammals,  and  especially  in  man,  as 
the  results  of  certain  errors  there  may  be  a  physiological  (or 
pathological)  reversion.  Hippuric  acid,  as  replacing  uric  acid 
in  the  herbivora,  may  be  regarded  in  a  similar  light. 

(^ur  knowledge  of  the  metabolism  of  the  spleen,  beyond  its 
relations  to  the  formation  of  (blood-cells/ and  their  disintegra- 
tion, is  in  the  suggestive  rather  than  the  positive  stage.  It 
seems  highly  probable  that  this  organ  plays  a  very  important 
part,  the  exact  nature  of  which  is  as  yet^nknown^ 

fWhen  an  animal  starves,  it  may  be  considered  as  feeding  on 
its  own  tissues,  the  more. active  and  important  utilising  the 
others.  Notwithstanding,  organs  with  i  very  active  metabo- 
lism, as  the  muscles  and  glands,  lose  weiq^ht  to  a  large  extent. 
The  presence  of  urea  to  an  amount  not  very  greatly  below  the 
average  in  health,  shows  that  there  is  an  active  proteid  metab- 
olism then  as  at  all  times  in  progress. 

( (General  experience  and  exact  experiments  prove  that,  while 
an  animal's  diet  may  be  supplied  with  special  regard  to  fatten- 
ing, to  increase  working  power,  or  simply  to  maintain  it  in 
health,  as  evidenced  by  breeding  capacity,  form,  etc.,  in  all  cases 
there  must  be  at  least  a  ^urtsin  minimum  quantity  of  each  of 
the  food-stuffs.  No  one  food  can  be  said  to  be  exclusively 
fattening,  heat-forming,  or  musple-forming. 

/A  carbohydrate  diet  tends  to  production  of  fat ;  flesh,  and 
oth^r  proteid  food  to  supply  muscular  energy,  but  the  latter 
also  produces  fat,  and  a  diet  of  flesh  mixed  with  fat  or  gelatin 
will  serve  the  purposes  of  the  econoiny  better  than  one  contain- 
ing a  very  much  larger  quantity  of  proteid  alone.    Muscular 
energy,  as  is  to  be  inferred  from  the  excreta,  is  not  the  result 
of  nitrogenous  metabolism  alone ;  and  in  arranging  any  diet 
for  man  or  beast  the  race  and  the  individual  must  be  consid- 
«red.    Animals  can  not  be  treated  as  machines,  like  engine!*) 
using  similar  quantities  of  fuel ;  though  this  holds  far  more  of p 
man  than  the  lower  animals — ^i.  e.,  the  results  may  be  predicted) 
from  the  diet  with  far  less  certainty  in  the  case  of  man  than  of i 
other  mammala 

(Food  is  related  to  excreta  in  a  definite  way,  so  tkat  all  that 
enters  as  food  must  sooner  or  later  appear  as  urea,  salts,  oar- 


tatla^v 


I 


nor  is  it  to 
id  complete 
ture  of  the 
dicate  that 
rolutionary 
in  man,  as 
ological  (or 
g  uric  acid 
t. 

,  heyond  its 

disintegra- 

9  stage.    It 

IT  important 

s  feeding  on 
tilising  the 
Ive  metabo- 
arge  extent, 
y  below  the 
)teid  metab- 

)  that,  while 
rd  to  f atten- 
intain  it  in 
.,  in  all  cases 
y  of  each  of 
exdusivdy 

t ;  flesh,  and 
it  the  latter 
at  or  gelatin 
one  contain* 
).    Muscular 
»t  the  result 
ing  any  diet 
st  be  consid- 
like  engine^N 
I  far  more  of  ^ 
be  predicted) 
man  than  of  1 

that  aU  that 
»,  salts,  oar- 


THK  METABOLISM  OP  THh   BODY.  4 

bonic  anhydride,  water,  etc.    These  are  individually  to  be 
garded  as  the  final  links  in  a  long  chain  of  metabolic  procat-    s 
or  rather  a  series  of  these.    Fats  and  carbohydrates  are  rej 
sented  finally  as  carbonic  anhydride  and  water  principally,  pro- 
teids  as  urea. 

(Nitrogenous  foods  may  be  regarded  as  accelerating  the 
metabolic  processes  generally  and  proteid  metabolism  in  par- 
ticular, while  fats  have  the  reverse  effect ;  hence  fat  in  the  diet 
renders  a  less  quantity  of  proteid  sufficient.  Qelatine  seems  to 
act  when  mixed  with  proteid  food  either  like  an  additional 
quantity  of  proteid,  or  possibly  like  fat,  at  all  events  under  such 
circumstances  less  proteid  sufficea 

These  facts  have  a  bearing  not  only  on  health  but  on  econ- 
omy, in  the  expenditure  for  food. 

(Baits  hold  a  very  important  place  in  every  diet,  though 
their  exact  influence  is  in  great  part  unknown.  The  heat  of 
the  body  is  the  resultant  of  all  the  metabolic  processes  of  the 
organism,  especially  the  oxidative  ones.  Certain  food-stuffs 
have  greater  potential  capacity  for  heat  formation  than  others ; 
but,  finally,  the  result  depends  on  whether  the  organism  can 
best  utilize  one  or  the  othdr. 

A  certain  body  temperature,  varying  only  within  narrow 
limits,  is  maintained,  partly  by  regulation  of  the  supply  and 
p^Iy  by  the  regulation  of  the  loss. 

nBoth  these  fure,  ia  health,  under  the  directicm  of  the  nervous 
system,  and  both  are  co-ordinated  by  the  same.  Ijoss  is  chiefly 
through,  the  skin  and  lungs ;  gain  chiefly  through  the  organs 
of  most  active  metabolism,  as  the  muscles  and  glands. 

Vaso-motor  effects  play  a  great  part  in  the  escape  of  heat. 

Animals  may  be  divided  into  poikilothermers  and  homoio- 
thermers,  or  cold-blooded  and  warm-blooded  animals,  accord- 
ing as  their  body  heat  varies  with  or  is  independent  of  the  ex- 
ternal changes  of  temperature.  All  the  facts  go  to  show  that 
in  mammals  the  processes  of  the  body  (metabolism)  can  con- 
tinue only  within  a  slight  range  of  variations  in  temperature, 
though  the  npwf^rd  limit  is  narrower  than  the  downward. 

(Jjpon  the  whole,  the  evidence  justifies  the  conclusion  that 
thenervo^_8yat§Si^  is  concerned  in  all  the  metabolic  processes 
of^lfiebody  in  mammals  including  man,  and  that,  as  we  descend 
the  scale,  the  dominion  of  the  nervous  system  becomes  less  till 
we  reach  a  point  when  protoplasm  goes  through  the  whole 
cycle  of  its  changes  by  virtue  of  its  own  properties  uninfluenced 
by  any  modification  of  itself  in  the  form  of  a  nervous  system. 


f 


mll^ 


480 


ANIMAL  PHYSIOLOGY. 


^ 


THE  SPINAL  CORD.—GENERAL. 

Among  the  higher  vertebrates  the  spinal  cord  is  found  to 
consist  of  nerve-cells,  nerve-fibres,  and  a  delicate  connective  tis- 
sue binding  them  together;  while  these  different  structures  are 
arranged  in  definite  forms,  so  that  a  cross-section  anywhere  pre- 
sents a  characteristic  appearance,  the  more  important  gangli- 
onic nerve-cells  being  internal  and  forming  a  large  part  of 


!      ; 


the  gray  matter  of  the  cord.  All  the  various  regions  of  this 
organ  or  series  of  organs  are  connected  with  one  another,  white 
wtth  white  and  gray  matter,  as  well  as  white  with  gray  sub- 


-im^metsmm 


THE  SPINAL  CORD.— GENERAL. 


481 


gtauce.    The  cord  may  be  regarded  either  as  an  instrument  for 
the  reception  and  generation  of  impulses  independent  of  the 


\  found  to 
lective  tis- 
ctures  are 
where  pre- 
nt  gangli- 
j^e  part  of 


ifaram;>,oM«bel- 

pons  of  this 
lother,  white 
ih  gray  sub- 


F».  SM.— TmwvOTw  Motion  of  mfaial  onrd  of  dtild  six  months  old,  at  middle  oC  lumbwr 
r«gion,iliowinKeq)eeiallytlwnMnio(gn»MtMtMice.  IxSO.  (Aftar Oerlnch.)  a,ante- 
rior  oMumna ;  b,  poaterlor  oolnmna ;  e,  Inwrnl  oolamM :  d.  nnt«rior  root* ;  e,  poaterior 
root* ;  /,  anterior  white  oomiiiliire :  g,  aauU'al  eanal  lined  by  epittiellal  eeUa ;  k,  oon- 
necUve-UHue  nbatanoe  aurroundlnK  It ;  t,  tnaa*crM  libers  of  gra/  oommlMure  in  iront, 
and  k,  the  same  behind  oentnri  canal ;  I,  two  reins  cot  across ;  m,  anterior  comua ;  n, 
great  lateral  ceU  group  of  anterior  oomua ;  o.  leaser  anterior  odi  gvMm  (oohunn) ;  p, 
smallMt  median  oril  group ;  g,  posterior  coraua ;  r,  ascending  CMwicttll  In  posterior 


brain ;  or  as  a  conductor  of  afferent  and  efferent  impulses  des- 
tined for  the  brain  or  originating  in  that  organ.  As  a  matter 
of  fact,  however,  it  is  better  to  bear  in  mind  that  the  cord  and 
brain  constitute  one  organ  or  chain  of  organs,  which,  as  we 
have  learned  from  our  studies  in  development,  are  differentia- 
tions of  one  common  track,  originating  from  the  epiblast. 

While  the  brain  and  the  cord  may  act  independently  to  a 
very  large  extent,  as  may  be  shown  by  experiment,  yet  it  can 
not  be  too  well  borne  in  mind  that  in  the  actual  normal  life  of 
an  animal  such  purely  independent  behavior  must  be  exceed- 
ingly rare.  We  are  constantly  in  danger,  in  studying  a  sub- 
ject, of  making  in  our  minds  isolations  which  do  not  exist  in 
nature.    When  one  accidentally  sits  upon  a  sharp  object,  he 

81 


t 


•im 


489 


ANIMAL  PHYSIOLOGY. 


rises  suddenly  without  a  special  efiEort  of  will  power ;  he  experi- 
ences  pain,  and  has  certain  thoughts  about  the  object,  etc. 


ria  MK.-anmD«>f  Mik  In  ootUMCtion  with  anterior  r«N)ti  of  •|rfMlMrTM,a«*9W 

■4S<rSS«»  ^  l^JTwSofSwpcSftBT  Flint  and  VtS^A.  emergwjce  oT  Mtertor 
SS  ftSn^  mSSrV^k.  ^^Si  connected  both  wKh  •«*  other  a >d  w^^ 

anterior  rooto. 

Now,  in  reality  this  is  v^ry  complex,  though  it  can  be  ana- 
lyzed into  its  factors.  Thus,  afferent  nerves  are  concerned,  the 
spinal  cord  as  a  reflex  center,  efferent  nerves  to  the  muscles 
called  into  action,  the  cord  as  a  conductor  of  impulses  which  re- 
sult in  sensations,  emotions  and  thoughts  referable  to  the  brain ; 
so  that  if  we  would  grasp  the  state  of  affairs  it  is  of  importance 


0mm 


atmam 


WMWM 


JJ. 


he  experi- 


M  i^eB  in  te«na- 
•nee  of  Miterlor 
>d  with  libera  of 


Ban  beana- 
icemed,  the 
she  muscles 
js  which  re- 
o  the  brain ; 
importance 


THE  SPINAL  CORD.— OENBRAL. 


488 


to  so  combine  the  various  processes  in  our  mental  conception 
that  it  shall  in  our  minds  form  that  whole  which  corresponds 


FialM. 


'^■J**-.:J?;¥?P-  yf-  •  'ffy'w  nerwmbir  Md  commanloMloa  of  Its  bnuKdiea  witli  bteUr 


with  nature,  as  we  have  been  insisting  upon  fn  the  last  chapter. 
With  this  admonition,  and  assuming  a  good  knowledge  of  the 


Wr»>)iiH»HBIw.'lwi|iiwi«M(*wPiw>- 


484 


ANIMAL  PHTSIOLOOT. 


fi^neral  and  minute  anatomy  of  the  spinal  cord,  we  shall  pro- 
ceed to  discuss  its  functions. 

The  Reflex  Functions  of  the  Spinal  Cord. 

The  following  experimental  observations  may  readily  be 
made  by  the  8tu^3nt  himself :  Let  a  decapitated  frog  be  sus- 
pended freely  (from  the  lower  jaw).  It  hangs  motionless  and 
limp  at  first,  but  when  it  recovers  from  the  shock  (abolition  of 
function)  to  the  spinal  cord  produced  by  the  operation,  it  may 
be  shown  that  this  organ  is  functional :  1.  When  a  piece  of 
bibulous  paper  dipped  in  dilute  acid  is  placed  upon  the  thigh, 
the  leg  is  drawn  up  and  wipes  away  the  offending  body.  21  If 
the  paper  be  placed  on  the  anus,  both  legs  may  be  drawn  up, 
either  successively  or  simultaneously.  3.  If  the  leg  of  one 
side  be  allowed  to  hang  in  the  dilute  acid,  it  will  be  withdrawn. 
4.  If  a  small  piece  of  blotting-paper  dipped  in  the  acid,  be 
placed  on  the  thigh,  and  the  leg  of  that  side  gently  held,  the 
other  may  be  drawn  up  and  remove  the  object. 

It  may  be  noticed  that  in  every  case  a  certain  interval  of 
time  elapses  before  the  result  follows.  Upon  increasing  the 
strength  of  the  acid  very  much  this  interval  is  shortened,  and 
the  number  of  groups  of  muscles  called  into  action  is  increased. 
Again,  th^  result  is  not  the  same  in  all  respects  when  the 
nerve  of  the  leg  is  directly  stimulated,  as  when  the  skin  first 
receives  the  impression.  Section  of  the  nerves  of  the  parts 
abolishes  these  effects ;  so  also  does  destruction  of  the  spinal 
cord,  or  the  part  of  it  with  which  the  nerves  of  the  localities 
stimulated  are  connected ;  and  more  dxact  experiments  show 
that  in  the  absence  of  the  gray  matter  the  section  of  the  pos- 
terior or  anterior  roots  of  the  nerves  also  renders  such  mani- 
festations as  we  have  been  describing  impossible. 

These  experiments  and  others  seem  to  show  that  an  afferent 
nerve,  an  efferent  nerve,  and  one  or  more  central  cells  are 
necessary  for  a  reflex  action ;  that  the  latter  ie  only  a  perfectly 
co-ordinated  one  when  the  skin  (end-organs)  and  not  the 
nerve-trunks  are  stimulated ;  that  there  is  a  latent  period  of 
stimulation,  suggesting  a  central  "summation"  of  impulses 
necessary  for  the  effect ;  that  the  reflex  is  not  due  to  the  mere 
passage  of  impulses  from  an  afferent  to  an  efferent  nerve 
through  the  cord,  but  implies  important  processes  in  the  cen- 
tral cells  themselves.  The  latter  is  made  further  evident  from 
the  fact  that  (I)  strychnia  greatly  alters  reflex  action  by  short- 


iiMkmm 


mimmium 


THE  SPINAL  C0RD.-6BKERAL. 


486 


mil  pro- 


D. 

adily  be 
5  besus- 
aless  and 
[)litioii  of 
n,  it  may 
,  piece  of 
he  thigh, 
iy.  ^If 
irawn  up, 
B^  of  one 
ihdrawn. 
I  acid,  be 
held,  the 

iterval  of 
wing  the 
ened,  and 
increased, 
when  the 
skin  first 
the  parts 
he  spinal 
localities 
mis  show 
f  the  pos- 
Lch  mani- 

n  afferent 
cells  ave 
perfectly 
not  the 
period  of 
impulses 
the  mere 

ant  nerve 
thecen- 

lent  from 
by  short- 


ening the  latent  period  and  extending  the  range  of  muscular 
action,  which,  it  has  been  shown,  is  not  due  to  changes  in  the 
nerves  themselves.  A  very  slight  stimulus  suflBces  in  this  in- 
stance to  cause  the  whole  body  of  a  decapitated  frog  to  pass 
into  a  tetanic  spasm.  We  must  suppose  that  the  processes 
usually  confined  to  certain  groups  of  central  cells  have  in  such 
a  case  involved  others,  or  that  the  "  resistance  "  of  the  centers 
of  the  cord  has  been  diminished,  so  that  many  more  cells  are 
now  involved;  hence  many  more  muscles  called  into  action. 
Normally  there  is  resistance  to  the  passage  of  an  impulse  to  the 
opposite  side  of  the  cord,  as  is  shown  by  the  fact  that  when  a 
slight  stimulus  is  applied  to  the  leg  of  one  side  the  reflex  is 
confined  to  this  member. 

It  is  evident,  then,  that  the  reflex  resulting  is  dependent  on 
(1)  the  location  of  the  stimulus,  (2)  its  intensity  and  duration, 
(3)  its  character,  and  (4)  the  condition  of  the  spinal  cord  at  the 
time.  Occasionally  on  irritating  one  fore-limb  the  opposite 
hind  one  answers  reflexly.  Such  is  a  "  crossed  reflex,"  and  is 
the  more  readily  induced  in  animals  the  natural  gait  of  which 
involves  the  use  of  one  fore-leg  and  the  opposite  hind-limb 
together. 

Reflexes  are  often  spoken  of  as  purposive,  and  suggest  at 
first  intelligence  in  the  cord ;  but  such  phenomena  are  explained 
readily  enough  without  such  a  strained  assumption. 

EwjiiUion,  heredity,  and  the  law  of  habit,  apply  here  as  else- 
where. The  relations  of  an  animal  to  its  environment  must 
necessarily  call  into  play  certain  nervo-muscular  mechanisms, 
which  from  the  law  of  habit  come  to  act  together  when  a 
stimulus  is  applied.  Naturally  those  that  make  for  the  welfare 
of  the  animal  are  such  as  are  most  used  under  the  influence  of 
the  intelligence  of  the  animal— i.  e.,  of  the  domination  of  the 
higher  cerebral  centers,  so  that  when  the  latter  are  removed  it 
is  but  natural  that  the  old  mechanisms  should  be  still  employed. 
Moreover,  the  reflex  movements  are  not  always  beneficial,  as 
when  a  decapitated  snake  coils  itself  around  a  heated  iron 
under  reflex  influence,  which  is  readily  enough  understood  if 
we  remember  the  tuihit  of  coiling  aroimd  objects,  and  what 
this  involves — vis.,  organised  tendencies. 

T^piiMMaii  of  BefoM,— It  can  be  shown  in  the  case  of  a  frog 
that  still  retains  its  optic  lobes  and  the  parts  of  the  brain  pos- 
terior to  them  that,  wh^n  these  are  stimulated  at  the  same  time 
as  the  leg,  the  reflex,  if  it  occurs  at  all,  is  greatly  delayed. 

On  the  othei*  hand,  in  the  case  of  d<^,  from  which  a  part 


iyaii)  i^JtHi^imdimm^ 


MP 


486 


ANIMAL  PHTSIOIiOOT. 


of  the  cerebral  cortex  has  been  removed,  the  refletes  are  much 
more  prominent  than  before.  Experience  teaches  us  that  the 
acts  of  defecation,  micturition,  erection  of  the  penis,  and  many 
others,  are  susceptible  of  arrest  or  may  be  prevented  entirely 
when  the  usual  stimuli  are  still  active,  by  emotions,  etc. 

These  and  numerous  other  facts  tend  to  show  that  the  higher 
centers  of  the  brain  can  control  the  lower;  and  it  is  not  to  be 
doubted  that  pure  reflexes  during  the  waking  hours  of  the 
higher  animals,  and  especially  of  man,  are,  much  less  numerous 
than  among  the  lower  vertebrates.  The  cord  is  the  servant  of 
the  brain,  and  a  faithful  and  obedient  one,  except  in  oases  of 
disease,  to  some  forms  of  which  we  have  already  referred. 

Certain  recent  experiments  iihow  in  the  clearest  way  how  the 
conditions  of  the  central  nervous  system,  and  especie^y  in  the 
first  instance,  the  brain  determines  the  reflex  time  to  which  we 
shall  presently  refer :  thus,  among  other  influences,  music  and 
even  different  airs  greatly  alter  the  reflex-time,  and,  indeed, 
the  whole  character  of  the  act  (tendon-reflex). 

It  is  not  to  be  supposed,  however,  that  the  processes  that 
are  clearly  cerebral,  and  which  modify  normal  reflexes  so 
greatly,  are  all  of  the  nature  of  inhibitions,  or  that  they  are 
at  all  fully  understood.  They  are  unquestionably  very  complex 
in  nature,  and  probably  too  intricate  to  be  completely  un> 
raveled. 

Btflnc  Time.— One  of  the  most  satisfactory  methods  of  ascer- 
taining the  length  of  time  a  reflex  act  occupies  is  the  follow- 
ing: Let  an  electric  stimulus  be  applied  to  one  of  the  eyelids, 
whereupon  both  blink.  The  whole  interval,  minus  the  latent 
period  of  the  orbicularis  muscle  and  the  time  occupied  in  the 
transmission  of  the  necessary  nervous  impulses  over  the  nerves 
concerned  (the  fifth  and  facial)  to  and  from  the  centers  involved 
(medulla),  giveis  the  duration  of  the  processes  in  the  brain-cells. 
The  whole  period  in  one  instence  was  '0662  seconds,  which,  re- 
duced as  indicated,  gives  '065S  as  the  time  required  for  the 
changes  that  take  place  in  the  brain-oells. 

It  will,  of  course,  be  understood  that  at  best  these  figures 
are  but  an  approximation,  owing  to  several  possible  sources  of 
error ;  also  that,  as  has  been  already  stated,  the  actual  period 
varies  with  the  condition  of  each  subject  at  the  time  of  ex- 
periment, not  to  mention  the  variations  for  individuals  and 
groups  of  animals.  In  the  instance  chosen  the  brain  itself  was 
the  center  involved,  but  the  same  laws  apply  to  the  reflex 
mechanisms  of  the  cord. 


1 

/ 


'iiiiiiiid laiwiii 


THE  SPINAL  COBD.-GBKBRAL. 


487 


The  Spinal  Cord  as  a  Conductor  of  Impulses. 

Before  considering  the  results  arrived  at  in  this  connection, 
some  brief  account  of  the  methods  applied  in  the  investigation 
of  the  subject  is  called  for,  to  enable  the  student  to  appreciate 
their  difficulties  and  possible  fallacies,  as  well  as  such  grounds 
of  certainty  as  there  may  be  for  the  conclusions  reached. 

Three  or  four  methods  of  research  have  been  employed :  1. 
Sections  of  the  spinal  cord  of  varying  extent,  both  unilateral 
and  bilateral.  In  estimating  the  value  to  be  attached  to  the 
symptoms  following,  the  difficulties  in  limiting  the  section,  the 
interference  of  haemorrhage,  the  inevitable  results  of  operative 
shock,  and,  as  in  all  experiments  on  the  nervous  system  of  ani- 
mals, the  danger  of  misinterpreting  the  symptoms,  must  be 
given  due  weight.  3.  Attempts  have  been  made  to  determine 
the  course  and  relations  of  nerve-fibers  by  ascertaining  the 
order  in  which  the  different  portions  of  the  spinal  nerve-fibers 
receive  their  investing  myelin,  those  with  the  longest  course 
being  the  latest  to  be  thus  completed.  This  is  the  method  of 
Fleohsig,  who  has  mapped  out  the  cord  into  a  series  of  columns, 
to  be  referred  to  again  presently.  The  method  is  open  to  the 
objection  of  all  anatomical  ones.  It  is  a  remarkable  fact  that, 
by  strictly  physiological  methods  (i  e.,  ascertaining  the  function 
of  parts),  nervous  tracts  have  been  traced,  which  were  quite 
unsuspected  as  the  result  of  anatomical  investigation  alone. 
Nevertheless,  this  method,  taken  with  others  now  under  con- 
sideration, has  rendered  important  service.  8.  Following  upon 
experimental  sections,  as  well  as  in  consequence  of  certain  dis- 
eases in  the  brain  and  cord,  fibers  have  been  found  to  degenerate 
along  certain  definite  paths,  owing,  it  is  believed,  to  being  cut 
off  from  their  trophic  centers;  so  that  if,  after  section  of  the 
cord,  there  is  degeneration  of  fibers  downward,  it  is  inferred 
that  the  trophic  cells  lie  above  the  seat  of  degeneration  and 
the  reverse.  This  may  be  called  the  pathological  (Wallerian) 
method,  and  in  conjunction  with  clinical  evidence  has,  in  the 
case  of  man  especially,  been  the  chief  source,  perhaps,  of  our 
knowledge  in  regard  to  the  conducting  paths  in  the  humAU 
cord;  though  other  methods,  as  carried  out  in  the  lower  ani- 
mals, have  yielded  results  which  have  been  supplementary  and 
corrective;  and  in  truth  a  variety  of  means  must  be  employed, 
and  the  greatest  caution  observed,  or  the  inferences  drawn  will 
be  partial  if  not  actually  erroneous. 

It  is  to  be  carefully  borne  in  mind  now,  and  when  studying 


I 


tmmSKmm 


Wfim>^ 


488 


ANIMAL  PHYSIOLOGY. 


the  brain,  that  a  conducting  path  in  the  nervous  centers  is  not 
synonymous  with  conducting  fibers.    The  cells  themselves  and 

the  neuroglia  probably  are  also 
conductors.  We  shall  now  en- 
deavor to  map  out,  as  estab- 
lished by  the  method  of  Flech- 
sig.  Waller,  and  others,  the 
main  fiber  tracts  of  tha  spinal 
cord. 

1.  Antero- median  Cdkmma 
(columns  of  Tdrck).  These 
probably  decussate  in  the  cerv- 
cial  region,  where  they  are  most 
marked,  constituting  the  direct 
or  uncrossed  pyramidal  trapt, 
and  disappear  in  the  lower  dor- 
sal region. 

Secondary  deg^eration  en- 
sues in  these  tracts  upon  cer- 
tain  brain-lesions,  in  the  motor 

2^S„±5'^^glSS5SS&S%!  regions. 

«.  Crossed  Pyramidai  Tracts. 
— ^"ihey  pass  forward  to  form 
part  of  the  anterior  pyramids  of 
the  medulla  after  decussation 
in  their  lower  part.  Similarly  to  the  first,  degeneration  follows 
in  tbese  tracts  when  there  are  brain-lesions  of  the  motor  area. 
H^ice,  both  of  these  constitute  descending  motor  paths. 

9.  Anterior  FasetcvH  (fundamental  or  ground  bundle). — 
They  possibly  connect  the  gray  matter  of  the  cord  with  that  of 
the  medulla. 

4.  Anterwr  Eadieular  Zones,  in  the  anterior  part  of  the  lat- 
eral column. 

6.  Miseed  Lateral  CoZuntTM.— These  and  tiie  preceding  are 
functionally  similar  to  &  Xeither  8,  4,  nor  6  degenerate,  on 
section  of  the  cord,  from  which  it  is  inferred  that  they  have 
trophic  cells  both  above  imd  below. 

6.  Dweel  Cerd>eaar  Tracis.—TheBe  bundles,  passing  by  the 
funiculi  graciles  or  posterior  pyramids  of  the  medulla,  reach 
the  cerebellum  by  its  inferior  peduncles. 

These  fasciculi  enlarge  from  their  site  of  origin  in  the  lum- 
bar cord  upward.  After  section  of  the  cord  they  show  ascend- 
ing degeneration,  so  that  it  seems  probable  that  their  trophic 


</ 

D 

Fia  S4B.— Dtagnmnuitlc  raprawntetioii  ot 
ootnmns  and  eonductbiir  paths  in  nAoal 
oocd  in  upper  danal  raKkn  (•ftw  rliii| 
MMlLMidob).    AR,AIt,witertor  roots  of 


umns) ;  B,  anterior  fimdameiital  tmteto- 
ttltts ;  C,  ooWmns  of  OoU  (  D,  columns  of 
Burdaoh  ;  B,  K,  anterior  radioulai  sooes; 


r. 


T,  miMd  lateral  coimnns: 
■id  nmunldal  tracta;  H,  H, 


"mm 


mmm 


bers  is  not 
elves  and 
y  are  also 
1  now  en- 
as  estab- 
of  Flech- 
hers,  the 
ihe  spinal 

Cdfwm/na 
.  These 
I  the  cerv- 
jT  are  most 
the  direct 
idal  traot. 
Lower  dor- 
ration  en- 
upon  cer- 
the  motor 

dfoJTVocto. 
1  to  form 
^ramids  of 
Bcussation 
on  follows 
lotor  area, 
bhs. 

bundle). — 
ith  that  of 

of  the  lat- 

seding  are 
inerate,  on 
they  hare 

ing  by  the 
tilla,  reach 

n  the  lum- 
ow  ascend- 
eir  trophic 


THE  SPINAL  CORD.— GENERAL. 

cells  are  to  be  referred  to  the  posterior  gray  comua  of  the  cord, 
which  they  connect  in  all  probability  with  the  cerebellum. 

7.  Columns  of  Burdock  (poetero-lateral  columns).— This 
tract  is  connected  with  the  restiform  bodies  and  reaches  the 
cerebellum  by  the  inferior  peduncles.  Secondary  degenera- 
tions do  not  occur  in  these  fasciculi,  so  that  it  seems  likely  that 
they  connect  nerve-cells  at  different  levels  in  the  cord;  and 
they  may  also  connect  the  posterior  gray  comua  with  the  cere- 
bellum as  6. 

Cohimna  of  QoU  (postero-median  columns).— They  do  not 
extend  beyond  the  lower  dorsal  or  upper  lumbar  region ;  and 
their  fibers  pass  to  the  funiculi  graciles  of  the  medulla.  As- 
cending degeneration  follows  section  of  these  columns. 

The  degenerations  referred  to  above  are  visible  by  the 
microscope,  and  of  the  character  following  section  of  nerves. 
It  is  probable  that  they  are  the  later  stages.of  a  primary  mo- 
lecular derangement  in  consequence  of  interference  with  that 
continuous  functional  connection  between  all  parts  on  which 
what  has  been  called  nutrition,  but  which  we  have  shown  is 
but  a  phase  of  a  complex  metabolism,  depends. 

BMonatioB. — Sections  of  the  cord,  when  confined  to  one  lat- 
eral half,  are  followed  by  paralysis  on  the  same  side  and  loss  of 
sensation,  confined  chiefly  to  the  opposite  half  of  the  body  be- 
low the  point  of  section.  The  results  of  experiment,  patho- 
logical investigation,  etc.,  have  rendered  it  clear  that— 1.  The 
great  majority  of  the  fibers  passing  between  the  periphery  and 
the  brain  decussate  somewhere  in  the  centers.  2.  Afferent 
fibers  cross  almost  directly  but  also  to  some  extent  along  the 
whole  length  of  the  cord  from  their  point  of  entrance,  the 
decussation  being,  however,  completed  before  the  medulla  is 
passed.  3.  Motor  or  efferent  fibers  decussate  chiefly  in  the 
medulla,  though  crossing  is  continued  some  distance  down  the 
cord,  such  latter  fibers  being  but  a  small  portion  of  the  whola 
This  fact  is  best  established,  perhaps,  by  noting  the  results  of 
brain-lesions.  With  few  exceptions,  susceptible  of  explanation,< 
a  lesion  of  one  side  of  the  cerebrum  is  followed  by  loss  of  motion^ 
of  the  opposite  side  of  the  body.  These  are  all  central,  well- 
established  truths.  It  is  also  now  pretty  well  determined  that  ^ 
voluntary  motor  impulses  descend  by  the  pyramidal  tracts, 
both  the  direct  and  the  crossed.  That  the  posterior  colunms  of 
the  cord  are  in  some  way  conowrned  with  sensory  impulses 
there  is  no  doubt;  but  when  an  attempt  is  made  to  decide 
details,  great  difficulties  are  encountered.     Bxperiments  on 


I 


490 


AmMAL  PHYSIOLOOT. 


animals  aire  of  necessity  very  unsatisfactory  in  such  a  case, 
from  the  difficulty  experienced  in  ascertaining  their  sensa- 
tions at  any  time,  and  especially  when  disordered. 

PathakffiflaL— A  good  deal  of  stress  has  been  laid  ui>on  the 
teachings  of  locomotor  ataxia  in  the  human  subject.  The 
symptoms  of  this  disease  are  found  associated  with  lesions  of 
the  posterior  columils  of  the  cord.  The  essential  feature  is  an 
inability  to  co-ordinate  movements,  though  muscular  power 
may  be  unimpaired.  But  such  inco-ordination  is  not  usually 
the  only  symptom;  and,  while  the  disease  seems  usually  to 
begin  in  Burdach's  columns,  the  columns  of  Gtoll,  the  posterior 
nerve-roots,  and  even  the  cells  of  the  posteirior  comtia,  may 
be  involved,  so  that  the  subject  becomes  very  complicated. 
Go-ordination  of  muscular  movements  is  normally  dependent 
upon  certain  afferent  sensory  impulses,  themselves  very  com- 
plex.   It  is  to  be  remembered  also  that  there  are  numberless 


V^mf. 


fto.  sir.— DtaiTun  to  ilhiitrale  pw*«M»  ("ww  J 


Iqr  Hbcra  c(  nervMOOli  OB 


connecting  links  between  the  two  sides  of  the  cord  and  be- 
tween its  different  columns  of  an  anatomical  kind,  not  to  men- 
tion the  possibly  numerous  physiological  (functional)  ones. 

We  have  stated  above  that  section  of  one  lateral  half  of  the 
cord  is  followed  by  loss  of  sensation  on  the  opposite  side  of  the 
body ;  but  directly  the  contrary  has  been  maintained  by  other 
observers ;  while  still  others  maintain  that  the  effects  are  not 


^^ 


;li  a  case, 
9ir  sensa- 

ui>on  the 
ject.  The 
lesions  of 
ktare  is  an 
lar  power 
>t  usually 
isually  to 
)  posterior 
■ntia,  may 
mplicated. 
dependent 
very  com- 
umberless 


OliOB 


rd  and  be- 
lot  to  men- 
l)one8. 
half  of  the 
side  of  the 
d  by  other 
ots'arenot 


THE  SPINAL  COBD.-OBXBRAL. 


491 


confined  to  one  side,  though  most  pronounced  on  the  side  of  the 
section.    The  same  remark  applies  to  motion. 

While  there  is  considerable  agreement  as  to  the  pyramidal 
tracts  of  the  lateral  column,  the  functions  of  the  rest  of  these 
divisions  of  the  cord  are  by  no  means  well  established.  It  is 
possible  that  vasomotor,  respiratory,  and  probably  other  kinds 
of  impulses,  pass  by  portions  of  the  lateral  tracts  other  than 
the  crossed  pyramidal.  When  a  lateral  half  of  the  cord  is 
divided,  the  loss  of  function  is  not  permanent  in  all  instances, 
but  has  been  recovered  from  without  any  regeneration  of  the 
divided  fibers ;  and  even  when  a  section  has  been  made  higher 
up  on  the  opposite  side,  partial  recovery  has  again  followed : 
so  that  it  would  appear  that  impulses  had  pursued  a  zigzag 
course  in  such  cases.  We  do  not  think  that  such  experiments 
show  that  impulses  do  not  usually  follow  a  definite  course,  but 
that  the  resources  of  nature  are  great,  and  that,  when  one  tract 
is  not  available,  another  is  taken. 

It  is  plain  that  impulses  do  not  in  any  case  travel  by  one 
and  the  same  nerve-fiber  throughout  the  cord,  for  the  size  of 
this  organ  does  not  permit  of  such  a  view  being  entertained ; 
at  the  same  time  there  is  i  relation  between  the  size  of  a  cross* 
section  of  the  cord  at  any  one  point  and  the  number  of  nerves 
connected  with  it  at  that  region. 


T  IT  m  n  I 
SMTtd. 


T  trm  n  I 
XwMter. 


iznTmvnnT  IT  m  B  I  vmranr  it  ut 
Bortot.  Ctmfeol. 


n  I 


Fto.  SIB.— IMatnm  to  tmatrate  rriattreaiid  itlMohiteuteiit  of  (l)gf«y  mirtt^ 

mBOi  lnwiei)iMlTB»wiiMwi«l«wMottpliialc(>rtLjaid(a)ieettoiial>wMoCaeTwml^^ 

We  may  attempt  to  trace  the  paths  of  impulses  in  the  cord 
somewhat  as  follows:  1.  Volitional  impulses  decussate  chiefly 
in  the  medulla  oblongata,  but  also,  to  some  extent,  throughout 
the  whole  length  of  the  spinal  cord.  They  travel  in  the  lateral 
columns  (crossed  pyramidal  tracts  chiefly,  if  not  exclusively), 
and  eventually  reach  the  anterior  roots  of  the  nerves  through 
the  anterior  gray  comua,  passing  to  them,  possibly,  by  the  ante- 


498 


ANIMAL  PHTSIOIiOOT. 


rioT  columns.  From  the  cells  of  the  anterior  cornna,  impulses 
travel  by  the  anterior  nerve-roots  to  the  motor  nerves,  by 
which  connection  is  made  with  the  muscles.  2.  Sensory  im- 
pulses enter  the  cord  from  the  afferent  nerve-fibers  by  the  pos- 
terior nerve-roots,  passing  probably  by  the  posterior  columns  to 
the  posterior  comua,  thence  to  the  lateral  columns,  decussation 
being  largely  immediate  though  not  completed  for  some  dis- 
tance up  the  cord. 


i      Ha^      6S24J      I' 


LOWER  LIMIT  OF 
MKDULU 


oerebelUr  flben ;  4, 4',  flben  retetad  to  "  mnfC^^ieiiM, 


ture.    Tha  motor 
il(«ateriorliorB). 

_._ Ithirttliew 

tpoaterior 

(Tt  would  seem  that  the  lateral  columns  are  the  great  high- 
ways of  impulses;  though  in  all  instances  it  is  likely  that  the 
gray  matter  of  tl^  cor^  plays  an  important  part  in  modify- 
ing them  before  they  reach  their  destination.    Some  observers 


MMiMiia 


la,  impttlBes 
nerves,  by 
Sensory  im- 
by  the  pos- 
>  columns  to 
decussation 
}r  some  dis- 


i.r. 


luUilr  a,«^,'<Hrect 
K  in  medulto ;  6,  E', 
r«tui«.  Tha  motor 
onl(«ateriorlion>). 

ft  upon  It. 


e  great  high- 
kely  that  the 
•t  in  modify- 
>me  observers 


THE  SPINAL  COKD.-QBNERAL. 


498 


believe  that  sensory  impulses  giving  rise  to  pain  travel  by  the 
gray  matter  of  the  cord  nlmost  exclusively.  It  would  be  easy 
to  lay  out  the  paths  of  impulses  in  a  more  definite  and  dog- 
matic manner ;  but  the  evidence  does  not  seem  to  warrant  it, 
and  it  is  better  to  avoid  making  statements  that  may  require 
serious  modification,  to  say  the  least,  in  a  few  months.  The 
prominent  principle  to  bear  in  mind  seems  to  be  that  while 
there  are  tracts  in  the  cord  of  the  animals  that  have  been  exam- 
ined and  probably  of  all  that  have  well-formed  spinal  cords, 
along  which  impulses  travel  more  frequently  and  readily  than 
along  others,  it  is  equally  true  that  these  paths  are  not  invaria- 
ble, nor  are  they  precisely  the  same  for  all  groups  of  animals. 
The  cord  can  not  be  considered  independently  of  the  brain ;  and 
there  can  be  no  doubt  that  the  paths  of  impulses  in  the  former 
are  related  to  the  constitution,  anatomical  and  physiological,  of 
the  latter.  It  is  still  a  matter  of  dispute  whether  the  cord  is 
itself  irritable  to  a  stimulus.  As  a  whole  it  is  without  doubt ; 
as  also  the  white  matter  by  itself.  The  gray  matter  is  certainly 
conducting,  but  whether  imtable  or  not  is  still  doubtfuL  Why 
the  sensibility  of  the  side  of  the  body  on  which  one  lateral  half 
of  the  cord  has  been  divided  should  be  increased  (hypereesthe- 
sia),  is  also  tmdetermined.  Possibly  it  is  due  to  a  temporary 
disturbance  of  nutrition,  or  the  removal  of  certain  usiutl  inhibi- 
tory influences  from  above,  either  in  the  cord  or  brain. 

Thb  Automatic  Functions  of  the  Spinal  Cobd. 

Reference  has  been  already  made  to  the  fact  that  when  por- 
tions of  a  mammal's  cerebrum  are  removed  the  reflexes  of  the 
cord  become  more  pronounced,  owing  apparently  to  the  removal 
of  influences  operating  on  the  cord  from  higher  centers. 

When  the  cord  itself  is  completely  divided  across,  it  often 
happens  (in  the  dog,  for  example)  that  there  are  rhythmic 
movements  of  the  posterior  extremities — ^i.  e.,  when  the  animal 
has  recovered  from  the  shock  of  the  operation — that  part  of  the 
cord  now  independent  of  the  rest  and  of  the  breftn  seems  to 
manifest  an  unusual  automatism.  The  question,  however,  may 
be  raised  as  to  whether  this  is  a  purely  automatic  effect,  or  the 
result  of  reflex  action.  But,  whichever  view  be  entertained, 
these  phenomena  certainly  teach  the  dependence  of  one  part 
upon  another  in  the  normal  animal,  and  should  make  one  cau- 
tious in  drawing  conclusions  from  any  kind  of  experiment,  in 
regard  to  the  normal  functions.    As  we  have  often  urged  in 


4M 


ANIMAL  PHTSIOLOOr. 


the  foregoing  chapters,  what  a  part  may  under  certain  circtun- 
stances  manifest,  and  what  its  behavior  may  be  as  usually 
placed  in  its  proper  relations  in  the  body,  are  entirely  different, 
or  at  least  may  be.  When  one  leg  is  laid  over  the  other  and  a 
sharp  blow  struck  upon  the  patella  tendon,  the  leg  is  jerked  up 
in  obedience  to  muscular  contraction.  It  is  not  a  little  difiScult 
to  determine  whether  this  result  is  due  to  direct  stimulation  of 
the  muscle  or  to  reflex  action,  the  first  link  in  the  chain  of 
events  necessary  to  call  it  forth  originating  in  the  tendon; 
hence  the  term  tendon-reflex.  But  at  present  it  is  safer  to 
speak  of  it  as  the  "  knee-jerk,"  or  the  "  tendon-phenomenon." 
It  disappears,  however^  when  the  spinal  cord  is  destroyed  or  is 
diseased,  as  in  locomotor  ataxia,  or  when  the  nerves  of  the 
muscles  or  the  posterior  nerve-roots  are  divided,  showing  that 
the  integrity  of  the  center,  the  nerves,  and  the  muscles  are  all 
essential.  There  are  normally  many  such  phenomena  (reflexes) 
besides  the  "  knee-jerk." 

Anol-her  question  very  difficult  to  decide  is  that  relating  to 
the  usual  condition  of  the  muscles  of  the  living  animal.  It  is 
generally  admitted  that  the  muscles  of  the  body  are  all  in  a 
somewhat  stretched  condition,  but  it  is  not  so  clear  whether 
the  skeletal  muscles  are  under  a  constant  tonic  influence  like 
those  of  the  blood-vessels.  It  is  certain  that,  when  the  nerves 
going  to  a  set  of  muscles  are  cut,  when  even  the  posterior  roots 
of  the  nerves  related  to  the  part  involved  are  divided  or  the 
spinal  cord  destroyed,  there  is  an  unusual  flaccidity  of  the 
limb  involved.  But  the  natural  condition  may  be,  it  has  been 
suggested,  the  result  of  reflex  action.  The  subject  is  probably 
more  complex  than  it  has  hitherto  been  considered. 

The  facts  of  such  a  case — those  of  the  tendon-phenomenon 
and  similar  ones— would  be  better  understood  if  the  spinal 
cord,  the  nerves,  and  the  muscles  associated  with  them,  were 
regarded  as  parts  of  a  whole  so  connected  in  their  functions 
that  severance  of  any  one  of  them  leads  to  disorder  of  the  rest. 
That  the  colls  of  the  cord  are  constantly  exercising  an  influence 
through  the  nerv^<s  on  the  muscles,  while  they  in  turn  do  not 
lead  an  independent  existence,  but  are  as  constantly  influenced 
by  afferent  impulses,  and  that  one  of  the  results  id  the  condi- 
tion of  the  muscles  referred  to,  is,  we  are  convinced,  the  case. 
To  say  that  it  is  either  entirely  automatic  or  purely  reflex,  or 
that  the  whole  of  the  facts  would  be  covered  even  by  any  com- 
bination of  these  two  processes,  would  probably  be  unjustifi- 
able. The  influence  of  the  centers  over  the  metabolism  of  parts 


'"iiiTWMMrawiimiiiiiiTiiiif  imnnf  iiimnHtmi 


THE  SPINAL  COBD.~OENBRAL. 


495 


un  oircurn- 
as  usually 
y  different, 
)ther  and  a 
}  jerked  up 
tie  difficult 
aulation  of 
le  chain  of 
be  tendon; 
is  safer  to 
momenon." 
>royed  or  is 
Tes  of  the 
owing  that 
jcles  are  all 
a  (reflexes) 

relating  to 
imal.  It  is 
are  all  in  a 
ar  whether 
Suence  like 
the  nerves 
terior  roots 
ided  or  the 
iity  of  the 
it  has  been 
is  probably 

henomenon 
the  spinal 
them,  were 
r  functions 
of  the  rest, 
ui  influence 
turn  do  not 
r  influenced 
3  the  condi- 
)d,  the  case, 
ly  reflex,  or 
)y  any  com- 
te  unjustifi- 
ism  of  parts 


is  both  constant  and  essential  to  their  well-being ;  and  in  such 
a  case  as  that  now  considered  it  may  be  that  a  certain  degree 
of  tonus  is  normal  to  a  healthy  muscle  in  its  natural  surround- 
ings in  the  body. 

There  is  now  considerable  evidence  in  favor  of  placing  cer- 
tain centers  presiding  over  the  lower  functions,  as  micturition, 
defecation,  erection  of  penis,  etc.,  in  the  spinal  cord  of  mam- 
mals, especially  its  lower  part — which  centers,  if  they  be  not 
automatic,  are  not  reflex  in  the  usual  sense ;  but  their  considera- 
tion is  better  attempted  in  connection  with  the  treatment  of 
the  physiology  of  the  parts  over  which  they  preside. 

Special  Considerations. 

OompantlTe. — Among  invertebrates  thev«  is,  of  course,  no 
spinal  cord,  but  each  segment  of  the  animal  is  enervated  by  a 
special  ganglion  (or  ganglia)  with  associated  nerves.  Never- 
theless, these  are  all  so  connected  that  there  is  a  co-ordination, 
though  not  so  pronounced  as  in  the  vertebrate,  iu  which  the 
actual  structural  bonds  are  infinitely  more  numerous,  and  the 
functional  ones  still  more  so.  From  this  result  possibilities  to 
the  vertebrate  unknown  to  lower  forms ;  at  the  same  time,  in- 
dependent life  and  action  of  parts  are  necessarily  much  greater 
among  invertebrates,  as  evidenced  especially  by  the  renewal  of 
the  whole  animal  from  a  single  segment  in  many  groups,  as  in 
certain  divisions  of  worms,  etc. 

It  also  follows  from  the  same  facts  that  a  vertebrated  ani- 
mal must  suffer  far  more  from  injury,  in  consequence  of  this 
greater  dependence  of  one  part  on  another ;  a  thousand  things 
may  disturb  that  balance  on  which  its  well-being,  indeed,  its 
very  life  hangs.  It  is  noticeable,  moreover,  that,  as  animals 
occupy  a  higher  place  in  the  organic  scale,  their  nervous  sys^ 
tern  becomes  more  concentrated;  ganglia  seem  to  have  been 
fused  together,  and  that  extreme  massing  seen  in  the  spinal 
cord  and  brain  of  vertebrates  is  foreshadowed.  In  the  chapters 
on  the  brain  numerous  illustrations  of  the  nervous  system  in 
lower  forms  will  be  found. 

^he  fact  that  the  brain  and  cord  arise  from  the  same  germ 
layer,  and  up  to  a  certain  point  are  developed  almost  precisely 
alike,  is  full  of  significance  for  physiology  as  well  as  morphol- 
ogy. That  original  deep-lying  coimection  is  never  lost,  though 
functional  differentiation  keeps  pace  with  later  morphological 
differentiation.    But  even  among  vertebrates  the  spinal  cord 


496 


ANIMAL  PHTSIOLOGY. 


shows  a  complexity  gradually  increasing  with  ascent  in  the 
organic  series.  In  the  lowest  of  the  fishes  or  vertebrates  {Am- 
phwxua  lanceolatus)  the  creature  possesses  a  spinal  cord  only 
and  no  brain,  so  that  an  opportunity  is  afforded  of  witness- 
ing how  an  animal  deports  itself  in  the  absence  of  those  direct- 
ive functions,  dependent  on  the  existence  of  higher  cerebral 
centers.  The  Lancelet  spends  a  greai  part  (>f  its  life  buried 
in  mud  or  sand  on  the  bottom  of  the  ocean,  and  its  existence  is 
very  similar  to  that  of  an  invertebrate,  though,  of  course,  the 
dependence  of  parts  on  each  other  is  somewhat  greater. 

BralntioB. — According  to  the  general  law  of  habit  and  in- 
heritance,  we  should  suppose  that  at  birth  each  group  of  ani- 
mals would  manifest  those  reflex  and  other  functions  of  the 
cord  which  were  peculiar  to  its  ancestors.  Observation  and 
experiment  both  show  that  reflexes,  etc.,  are  hereditary ;  that 
they  tend  to  become  more  and  more  so  with  each  generation ; 
and  at  the  same  time  that  habit  or  exorcise  is  essential  for  their 
perfect  development.  They  stand,  in  fact,  in  the  same  relation 
as  instincts,  which  are  closely  connected  with  them.  Like  the 
latter,  they  may  be  modified  by  way  of  increase  or  diminution 
and  otherwise.  To  illustrate,  it  can  not  be  doubted  that  gallop- 
ing is  the  natural  gait  of  horses,  as  shown  by  the  tendency  of 
even  good  trotters  to  "break"  or  pass  into  a  gallop;  but  it  is 
equally  well  known  that  famous  trotters  breed  trotters.  In 
other  words,  an  acquired  gait  becomes  organized  in  the  nervous 
system  (especially)  of  the  animal,  and  is  transmitted  with  more 
and  more  fixity  and  certainty  with  the  lapse  of  time.  But  all 
experience  goes  to  show  that  walking,  running,  or  any  of  the 
movements  of  animals  are,  when  fully  formed  as  habit-reflexes, 
dependent  for  their  initiation  on  the  will  in  most  but  not  all 
instances,  and  require  for  their  execution  certain  combinations 
of  sensory  and  other  afferent  impulses,  and  the  integrity  of  a 
vast  complex  of  nervous  connections  in  the  spinal  cord. 

J  I  is  well  known  that  one  in  a  period  of  absent-mindedn^ 
walk  into  a  building  to  which  he  was  accustomed  to  go 
years  before,  though  not  of  late,  showing  plainly  that  volition 
was  not  momentarily  required  for  the  act  of  walking  and  all  else 
that  is  involved  in  the  above  behavior.  It  suggests  that  certain 
nervous  and  muscular  connections  have  been  formed,  function- 
ally at  least.  Plainly,  then,  we  should  not  expect  each  indi- 
vidual man's  spinal  cord  to  be  the  same,  but  that  the  series  of 
mechanisms  of  which  every  spinal  cord  is  made  up  should  differ 
with  experience ;  and  if  this  holds  for  individuals,  how  much 


cent  in  the 
brates  (Am- 
kl  cord  only 
of  witness- 
ihose  direct- 
ler  cerebral 
life  buried 
existence  is 
'  course,  the 
ater. 

ibit  and  In- 
roup  of  ani- 
tions  of  the 
rvation  and 
ditary;  that 
generation ; 
bial  for  their 
ame  relation 
a.    Like  the 
r  diminution 
i  that  gallop- 
tendency  of 
>p;  but  it  is 
trotters.    In 
I  the  nervous 
)d  with  more 
me.    But  all 
r  any  of  the 
abit-reflexes, 
)  but  not  all 
sombinations 
ategrity  of  a 
cord. 

t-mindedn^ 
itomed  to  go 
that  volition 
g  and  all  else 
9  that  certain 
led,  function- 
3t  each  indi- 
the  series  of 
should  differ 
s,  how  much 


THE  SPINAL  CORD.-OENERAIi. 


497 


more  must  it  be  true  of  different  groups  of  animals,  the  habits 
of  which  differ  so  widely !  Experiment  has  proved  this  also  so 
far  as  it  has  gone ;  hence  the  great  danger  of  laying  down  laws 
for  the  spinal  cord  from  the  investigation  of  one  animal  or 
even  one  group.  Recent  investigations  have  shown  that,  in 
persons  crippled  from  birth,  or  for  long  periods,  reflexes  which 
had  never  been  properly  established  may,  as  the  result  of  opera- 
tive procedure,  become  possible  through  training.  It  has  also 
been  shown,  both  by  experiment  Mid  clinical  experience  of  the 
kind  referred  to,  that  when  certain  reflexes  are  imperfectly  de- 
veloped others  are  also  defective,  again  impressing  the  im- 
portance of  that  balance  of  development  which  is  essential  to 
health  or  the  normal  condition  of  an  animal.  This  subject  is 
very  wide,  of  great  practical  importance,  and  deserves  consider- 
ation beyond  what  our  limits  of  space  will  allow. 

All  the  facts  go  to  show  that  the  cord  is  made  up  of  nervous 
mechanisms — if  we  may  so  speak — which  are  naturally  associ- 
ated, both  structurally  and  functionally,  with  certain  nerves 
and  muscles ;  these,  like  the  paths  which  impulses  take  to  and 
from  the  brain,  though  usual,  are  not  absolutely  fixed,  though 
more  so  as  reflex  than  conducting  paths,  while  they  are  con- 
stantly liable  to  be  modified  in  action  by  the  condition  of 
neighboring  groups  of  mechanisms,  etc. 

We  have  said  less  about  the  gray  matter  of  the  cord  as  a 
conductor  than  its  importance  perhaps  deserves.  It  is  believe^  \ 
by  many  that  impulses  which  give  rise  to  sensations  of  pain/ 
always  travel  by  the(gfray  mattery  and  there  is  not  a  little  evi-' 
dence  to  shoW  that,  when  none  of  the  white  columns  are  avail- 
able owing  to  operative  procedure,  disease,  or  other  disabling 
cause,  the  gray  matter  will  conduct  impulses  that  usually  pro- 
ceed by  other  tracts. 

BjnoptieaL — The  spinal  cord  is  composed  of  large  ganglionic 
nerve-cells,  fibers,  and  connecting  neuroglia.  Functionally  it 
is  a  conductor,  the  seat  of  certain  automatic  centers  and  of 
reflex  mechanisms.  Probably  in  every  case  the  one  function  is 
to  a  certain  extent  associated  with  the  other — i.  e.,  when  the 
(X>rd  acts  reflexly  it  is  also  a  conductor,  and  the  cells  concerned 
are  so  readily  excited  to  certain  discharges  of  nervous  energy 
that  automaticity  is  suggested,  and  so  in  other  instances:  thus, 
in  the  case  of  automaticity,  reflex  influence  or  afferent  impulses 
are  with  difficulty  entirely  excluded  from  consideration. 

The  great  majority  of  conducting  fibers  seem  to  cross  either 
in  the  cord  itself  or  in  the  medulla  oblongata.    The  conducting 
n 


i 


■5 


1 


I 


WIMDKHllMtlWI 


iiMiBiMMmiiawnaMMMiiiii^ 


*#* 


498 


ANIMAL  PHYSIOLOGY. 


paths  that  have  been  shown  by  pathological  and  clinical  inves- 
tigation to  be  best  marked  out  in  the  spinal  cord  are  those  for 
voluntary  motor  impulses.    So  far  as  the  functions  of  the  hu- 
man organ  are  concerned,  clinical  and  pathological  facts  have 
thrown  the  greatest  amount  of  direct  light  on  the  subject;  but 
the  inferences  thus  drawn  have  been  modified  and  supple- 
mented by  the  results  of  experiments  on  certain  other  mam- 
It  is  especially  important  to  bear  in  mind  that,  while  certain 
conducting  paths  are  usual,  they  are  not  invariable;  in  like 
manner,  reflex  impulses  may  not  be  confined  to  usual  groups  of 
cells,  but  may  extend  widely,  and  so  bring  into  action  a  large 
number  of  muscles.    The  resulting  reflex  in  any  case  is  depend- 
ent on  the  character,  intensity,  and  location  of  the  stimulus, 
and  especially  on  the  condition  of  the  central  cells  involved. 
In  the  whole  functional  life  of  the  cord  the  influence  of  higher 
centers  in  the  organ  itself  and  especially  in  the  brain  is  to  be 
considered.    The  cord  is  rather  a  g^up  of  organs  than  a  single 
one. 


s. 


THE  BRMN. 

The  methods  of  investigating  the  functions  of  the  brain  are 
analogous  to  those  employed  for  the  cord,  and  may  be  classed 
as  physiological  proper  and  pathological,  though,  as  a  matter 
of  fact,  neither  one  nor  the  other  is  now  considered  as  reliable 
when  taken  alone.  With  the  pathological  is  generally  in- 
cluded the  clinical  method;  and  the  conclusions  thus  derived, 
are  corrected  and  supplemented  by  the  results  obtained  by  sec- 
tion, removal,  or  other  operative  procedure  affecting  parts  of 
the  brain.  The  difiRculties  are  still  great-er  than  in  the  case  of 
the  cord;  ob  account  of  the  extreme  complexity  of  the  organ, 
especially  in.  the  higher  mammals  and  man. 

At  the  outset  we  may  remark  that  the  whole  subject  will 
be  studied  more  profitably  if  it  be  borne  in  mind  that— 1.  The 
brain  is  rather  a  collection  of  organs,  bound  together  by  the 
closest  anatomical  and  physiological  ties  than  a  single  one;  in 
consequence  of  which  it  is  quite  impossible  to  understand  the 
normal  function  of  one  part  without  constantly  bearing  in 
mind  this  relationship.  This  aspect  of  the  subject  has  not  re- 
ceived the  attention  it  deserves.  No  one  regards  the  aliment- 
ary tract  as  a  single  organ ;  but  it  is  likely  that  the  dependence 
functionally  of  one  part  of  the  digestive  oanal  upon  another 


_i>4&S3|WKi£& 


oical  invea- 
re  those  for 
;  of  the  hu- 
facts  have 
abject;  but 
ind  supple- 
other  mam' 

hile  certain 
ble;  in  like 
al  groups  of 
stionalarge 
ie  is  depend- 
lie  stimulus, 
[la  involved. 
ce  of  higher 
rain  is  to  be 
han  a  single 


he  brain  are 
iy  be  classed 
,  as  a  matter 
d  as  reliable 
generally  in- 
thus  derived, 
ained  by  sec- 
ting  parts  of 
in  the  case  of 
>f  the  organ, 

subject  will 
thai— 1.  The 
lather  by  the 
dngleone;  in 
iderstand  the 
bearing  in 
lot  has  not  re- 

the  aliment- 
le  dependence 
upon  another 


THE  BRAIN. 


499 


is  not  more  intimate  than  that  established  in  that  great  collec- 
tion of  organs  crowded  together  and  making  up  the  brain.  2. 
Since  the  relative  size,  position,  and  anatomical  connections  of 
the  parts  that  make  up  the  brain  are  different  in  different 
groups  of  animals,  not  to  speak  of  the  fact  that  the  functions 
of  any  part  of  the  brain  of  an  animal,  like  that  of  its  spinal 
cord,  already  alluded  to,  must  depend  in  great  part  upon  its 
own  and  its  inherited  ancestral  experiences,  it  follows  that  the 
greatest  caution  must  be  exercised  in  applying  conclusions 
true  of  one  group  of  animals  to  another.  As  we  shall  point 
out,  the  neglect  of  this  precaution  has  led  to  needless  contro- 
versy and  much  misunderstanding.  3.  It  follows,  from  what 
has  been  referred  to  in  1  above,  that  conclusions  based  upon  the 
behavior  of  an  animal  after  section  or  removal  of  a  part  of  the 
brain  must  be,  until  at  least  corrected  by  other  facts,  received 
with  some  hesitation.  4.  It  also  might  be  inferred  from  1  that 
it  is  desirable  to  study  the  simpler  forms  of  brain  found  in  the 
lower  vertebrates,  in  order  to  prepare  for  the  more  elaborate 
development  of  the  encephalon  in  the  higher  mammals  and  in 
man.  6.  The  embryological  development  of  the  organ  also 
throws  much  light  upon  the  whole  subject. 

The  student  will  see  from  these  remarks  that  a  sound  knowl- 
edge of  the  anatomy  of  the  brain  and  its  connections  is  indis- 
pensable for  a  just  appreciation  of  its  physiology;  nor  must 
such  knowledge  be  confined  to  the  human  or  any  other  single 
form  of  the  organ.  There  is  only  one  way  by  which  this  can 
be  attained :  dissection,  with  the  help  of  plates  and  descriptions. 
The  latter  alone  frequently  impart  ideas  that  are  quite  errone- 
ous, though  they  serve  an  especially  good  purpose  in  helping  to 
fix  the  pictures  of  the  natural  objects,  and  iu  reviving  them 
when  they  have  become  dim. 

It  is  neither  difficult  to  obtain  nor  to  dissect  the  brain  of  the 
fish,  frog,  bird,  etc.  Valuable  material  may  be  saved  and  the 
subject  approached  profitably,  if,  prior  to  the  dissection  of  a  hu- 
man brain,  a  few  specimens  from  some  group  or  groups  of  the 
domestic  animals  be  examined.  However  useful  artificial  brain 
preparations  may  be,  they  are  so  far  from  nature  in  color,  con- 
sistence, and  many  other  properties,  that,  taken  alone,  they  cer- 
tainly may  serve  greatly  to  mislead ;  and  we  hope  the  student 
will  allow  us  to  urge  upon  him  the  methods  above  suggested 
for  getting  real  lasting  knowledge.  The  figures  given  below 
may  prove  helpful  when  supplemented  as  we  advise. 

The  great  difference  in  total  size,  and  in  the  relative  propor- 


wiwiiirittMi:;i'iiMiiti(iiMiiiaw 


mmm 


600 


ANIMAL  PHYSIOLOGY. 


tion,  situation,  etc.,  of  parts,  will,  however,  be  obvious,  from 
the  figures  themselves;  and  as  we  have  already  pointed  out 
more  than  once,  the  preponderance  of  the  cerebrum  in  man 
must  ever  be  borne  in  mind  in  the  consideration  of  his  entire 
organization,  whether  physical,  mental,  or  moral ;  or,  to  put 
the  matter  otherwise,  all  man's  functions  are  the  better  under- 
stood by  the.  remembrance  of  this  one  fact,  which  will  be  at 
once  illustrated  when  we  consider  the  result  of  removal  of  the 
cerebrum  in  animals. 

Animals  dbpkivbd  op  the  Cerebrum. 

The  cerebrum  may  be  readily  removed  from  a  frog,  without 
producing  either  severe  prolonged  shock  or  any  considerable 
hromorrhage.  Such  an  animal  remains  motionless,  unless  when 
stimulated,  though  in  a  somewhat  different  position  from  that 
of  a  frog  having  only  its  spinal  cord.  It  can,  however, 
crawl,  leap,  swim,  balance  itself  on  an  inclined  plane,  and  when 
leaping  avoid  obstacles.  One  looking  at  such  an  animal  per- 
forming these  various  acts  would  scarcely  suspect  that  any- 
thing was  the  matter  with  it,  so  perfectly  executed  are  its 
movements.  We  are  forced  to  conclude,  from  its  remaining 
quiet,  except  when  aroused  by  a  stimulus,  that  its  volition  is 
lost ;  but,  apart  from  that,  and  ttie  fact  that  it  evidratly  does 
not  see  as  well  as  before,  it  appears  to  be  normal,  (it  has^p 
intelligenWireotive  power  over  its  movements.  It  remains, 
ThereiOTe,  to  ejq^ainTiow  irtrtfiatrttSey  are  so  much  more 
complete,  so  much  better  co-ordinated  in  the  entire  animal  than 
when  only  the  spinal  cord  is  left.  It  seems  to  be  legitimate  to 
infer  that  the  other  parts  of  the  brain  contain  the  nervous 
machinery  for  this  work,  which  is  usually  stimulated  to  action 
by  the  will,  but  which  an  external  stimulus  may  simulate.  All 
the  connections,  structural  and  functional,  are  present,  except 
those  on  which  successful  volition  depends.  The  frog  with  the 
cord  only,  sinks  at  once  when  thrown  into  water;  when  gently 
placed  on  its  back,  it  may  and  probably  will  remain  in  that 
position,  without  an  attempt  at  recovery.  There  is,  in  fact, 
verv  limited  power  of  co-ordination. 

Removal  of  the  cerebral  lobes  in  the  bird  is  more  likely  to 
be  attended  with  diflttculties,  and  conclusions  must  be  drawn 
with  greater  caution. 

But  a  pigeon  may  be  kept  alive  after  such  an  operation  for 
months.    It  can  stand,  balancing  on  one  leg ;  recover  its  posi- 


vions,  from 
pointed  out 
iim  in  man 
f  his  entire 
;  or,  to  put 
Btter  under- 
i  will  be  at 
loval  of  the 


rog,  without 
sonsiderable 
unless  when 
n  from  that 
n,  however, 
le,  and  when 
[  animal  per- 
ct  that  any- 
ated  are  its 
18  remaining 
8  volition  is 
idently  does 
1.  (tt  has  jip 
It  remains, 
much  more 
animal  than 
legitimate  to 
the  nervous 
,ted  to  action 
mulate.    All 
eeent,  except 
'rog  with  the 
when  gently 
ooaib  in  that 
e  is,  in  fact, 

ore  likely  to 
ist  be  drawn 

)peration  for 
aver  its  posi- 


THE  BRAIN. 


601 


tion  when  placed  on  its  side;  fly  when  thrown  into  the  air; 
it  will  even  preen  its  feathers,  pick  up  food,  and  drink  water. 
/Its  movements  are  such  as  might  be  those  of  a  stupid,  drowsy, 
lor  probably  intoxicated  bird;  but  it  is  plainly  endowed  with 
'.vision,  though  not  as  good  as  before.  But  spontaneous  move- 
ments are  absent,  and  the  peeking  at  food,  etc.,  must  be  consid- 
ered as  associated  reflexes,  and  as  such  are  very  interesting,  in 
that  they  show  how  machine-like,  after  all,  many  of  the  appar- 
ently volitional  acts  of  animals  really  are.  In  a  mammal  so 
great  is  the  shock,  etc.,  resulting  from  the  operative  procedure, 
that  the  actual  functions  of  the  remaining  parts  of  the  brain, 
when  the  cerebral  convolutions  are  removed,  are  greatly  ob- 
scured ;  nevertheless,  little  doubt  is  left  on  the  mind  that  homol- 
ogous parts  discharge  analogous  functions.  It  can  walk,  run, 
leap, right  itself  when  placed  inan  unnatural  position,  eat  when 
food  is  placed  in  its  mouth,  and  avoid  obstacles  in  its  path, 
though  not  perfectly.  Yet  it  remains  motionless  unless  stimu- 
lated ;  all  objects  before  its  eyes  impress  it  alike  if  at  all.  (j^e 
animal  evidently  has  neither  volition  nor  intelligence;  Now,  if 
iny  of  the  parts  between  the  oerebrum  and  the  medulla  be 
removed,  the  creaturer  shows  lessened  co-ordinating  power ;  so 
that  the  inference,  that  these  various  parts  are  essential  consti- 
tuents of  a  complex  mechanism,  all  the  components  of  which 
are  necessary  to  the  highest  forms  of  muscular  co-ordination 
and  probably  other  functions,  is  unavoidable. 

rrhere  are  all  degrees  of  consciousness,  and  it  is  quite  impos- 
sible  to  determine  the  extent  to  which  this  is  interfered  with 
in  animals  treated  as  described.  While  there  can  be  no  doubt 
that  for  th»  possession  of  the  higher  forms  of  consciousness  (as 
for  the  perfection  of  all  visual  and  other  sensory  processes)  the 
Voere]^um_i8  necessary.  It  would,  however,  be  very  hazardous 
to  state  that,  apart  from  this  part  of  the  brain,  consciousness 
did  not  exist.  Whe^  the  whole  enoephalon  is  removed,  the 
spinal  cord  alone  remaining,  it  would  not  be  legitimate  to  in- 
fer consciousness  in  the  sense  in  whioE  that  word  is  tisuaily 
implied ;  at  the  same  time,  in  the  intact  vertebrate,  we  may 
believe  that  consciousness  is  in  some  sense,  at  least  re- 
lated in  indefinable  ways  to  all  the  vital  processes,  if  not 
their  actual  resultant ;  inasmuch  as,  either  directly  or  indi- 
rectly, the  nervous  system  in  all  its  parts  is  functionally  con- 
nected, and  influences  and  is  itself  influenced  by  every  cell  in 
the  body. 

Since  we  are  dealing  with  co-ordinated  movements,  we  may 


I 


* 


, 


I 


602 


ANIMAL  PHYSIOLOGY. 


how  treat  of  the  functions  of  a  portion  of  the  ear,  according  to 
our  present  classification. 

Have  the  Sehicibcular  Canals  a  Go-ordinatino 

Function  ? 

Physiologists  have  as  yet  heen  unable  to  assign  to  the  semi- 
circular canals  a  function  in  hearing,  and  upon  certain  results, 
partly  of  disease  but  chiefly  of  experiment,  it  has  been  con- 
cluded, though  somewhat  dubiously,  that  they  are  concerned 
with  those  sensations  that  conduce  to  or  are  essential  to  main- 
tenance of  the  sense  of  equilibrium ;  in  a  word,  that  they  are 
the  organs  of  that  sense  in  the  samb  way  that  the  eye  is  the 
organ  of  vision. 

Iq^triawAtaL— When  in  a  bird,  as  a  pigeon,  one  of  the  mem- 
branous semicircular  canals'On  one  side  is  cut  through,  move- 
ments of  the  head,  varying  with  the  canal  cut,  result ;  though 
these  are  not  permanent,  when  the  operation  is  unilateral. 
After  the  bilateral  operation  a  bird  flies  with  difficulty,  eats  and 
drinks,  but  not  as  usual,  and  behaves  generally  in  a  way  to  in- 
dicate loss  of  co-ordination.  It  appears  to  be  dizzy.  It  can  hear 
well,  and  is  not  paralyzed,  nor  is  there  even  weakness  of  the 
muscles.  The  phenomena  in  other  animals,  while  not  quite  the 
same,  indicate  that  the  essential  failure  is  in  co-ordination  of 
muscular  movements.  When  the  peculiar  movements  of  the 
head  or  eyes,  at  first  ensuing  on  operation,  are  permanent,  it  is 
iwssible  that  there  may  have  been  injury,  either  primary  or 
secondary,  to  the  cerebellum  or  other  parts  of  the  brain.  There 
are  Very  many  ways  in  which  giddiness  and  consequent  inco^ 
ordination  may  be  induced  in  man  and  the  lower  animals. 
When  this  is  brought  about  by  rapid  rotation,  both  the  disturb- 
ance in  the  distribution  of  the  blood  within  the  cranium  and 
actual  displacement  of  brain-substance,  or  at  least  molecular 
disorder,  must  be  at  the  bottom  of  the  matter. 

^  Meniere's  disease,  vertigo  is  a  prominent  symptom  in 
certain  cases,  but  absent  in  others.  Again,  it  is  asserted  that 
vertigo  may  be  induced  in  animals  in  which  both  auditory 
nerves  are  divided.  For  our  own  part,  we  lielieve  an  undue  im- 
portance has  been  attached  to  the  sen  xiular  canals  in  the 
present  connection.  Experiments  on  an  mals  can  not  aJone 
solve  such  problems  as  this,  for  the  reason  that  we  can  never 
know,  except  in  the  vaguest  way,  their  states  of  consciousness. 
Indeed,  the  latter  must  always  be  interpreted  by  our  own,  or 


THE  BBAIN. 


608 


Eiccording  to 


[NATINQ 

to  the  semi- 
"tain  results, 
IS  been  con- 
's concerned 
tial  to  main- 
hat  they  are 
le  eye  is  the 

of  the  mem- 
■ough,  move- 
mlt ;  though 
s  unilateral, 
ilty,  eats  and 
a  way  to  in- 

It  can  hear 
kness  of  the 
aot  quite  the 
ordination  of 
nents  of  the 
manent,  it  is 

primary  or 
>rain.  There 
lequent  inco^ 
irer  animals. 
1  the  disturb- 
cranium  and 
st  molecular 

symptom  in 
asserted  that 
oth  auditory 
an  undue  im- 
canals  in  the 
oi  not  alone 
ve  can  never 
onsciousness. 
r  our  own,  or 


remain  inscrutable ;  so  that  it  follows  that  human  conscious- 
ness must  be  the  final  court  of  appeal ;  and  that  we  must  de- 
pend more  upon  clinical  and  pathological  investigation  than 
upon  experiment ;  but  even  this  is  not  final,  and  in  the  end  our 
own  conscious  experience  will  alone  enable  us  to  interpret  facts 
of  the  character  now  discussed.  Assume  that  a  human  subject 
has  been  operated  upon  as  above  indicated,  and  feels  so  dizzy 
that  he  is  unable  to  walk  steadily,  and  ]>o8sibly  unable  to  re- 
main standing.  If  interrogated,  what  would  be  the  answers 
given  by  an  accurate  reporter,  with  no  bias  from  any  theory 
whatever  bearing  on  thfi  subject  ?  As  we  conceive,  somewhat 
as  follows:  "How  d'  y  u  feel ?  Why  can  you  not  rise  and 
remain  standing,  or  ytuik  i"  "I  feel  all  confused.  I  can  not 
stand  or  walk  because  I  do  not  seem  to  be  able  to  make  out 
what  I  should  do.  I  have  no  clear  ideas  of  things  about  me, 
and  so  do  not  know  how  to  proceed."  Put  in  more  abstract  or 
generalized  form,  this  amounts  to  saying :  "(£>m  so  confused 
by  conflicting  sensations  that  all  my  old  judgments  about  the 
world  are  upset,  yet  memory  and  reason,  in  so  far  as  I  can  exer- 
cise them,  tell  me  that  they  are  wrong,  and  I  fear  to  act,  and  so 
remain  still ;  or,  when  I  do  try  to  stand  or  walk,  my  confusion 
leads  to  a  sort  of  loss  of  control  over  my  thoughts  and  feelings, 
and  therefore  my  will-power,  so  that  any  effort  to  walk  is  fee- 
bly directed  by  will,  and  little  regulated  by  my  usual  feelings; 
hence  I  accomplish  little,  and  lose  confidence  in  myself^  Such 
may  be  considered  an  attempt,  and  only  fairly  successful,  no 
doubt,  so  great  is  the  complexity  of  the  state  of  consciousness 
resulting,  to  describe  the  condition  of  a  human  being  under 
such  circumstances,  as  derived  from  a  consultation  with  our 
experiences  under  peculiar  conditions,  as  the  various  forms  of 
giddiness,  intense  and  sudden  surprise,  and  a  host  of  others  not 
readily  named  but  still  real.  With  a  bird  or  quadruped  the 
case  must  be  somewhat  similar. 

It  has  been  suggested  that  there  is  experimental  evidence  to 
show  a  power  of  estimation  of  the  distance  and  direction  through 
which  a  human  subject  is  moved,  independent  of  the  data  fur- 
nished by  other  senses,  as  sight,  tactile,  and  muscular  sensation, 
etc.  When  an  individual,  blindfolded,  lies  upon  a  flat  surface 
and  is  gently  rotated  through  a  certain  angle,  it  is  said  that  the 
subject  of  the  experiment  can  make  a  fair  estimate  both  of  the 
direction  and  distance  through  which  he  is  moved,  from  which 
it  is  argued  that  there  is  a  sense  answering  to  this  result,  and 
located,  presumably,  in  the  semicircular  canals.    But,  in  the 


f. 


I 


I 


iiaimmKmiimiiikmalm 


inwwii.iiWiiwiniiii'iiiiu 


604 


ANIMAL  PHYSIOLOGY. 


first  place,  we  very  much  doubt  whether,  in  such  »n  experi- 
ment, tactile  and  muscular  sensation  is  in  abeyance,  and,  in 
the  second  place,  if  it  were,  there  are  associated  sensations,  pos- 
sibly from  the  vascular  and  lymphatic  systems,  and  many 
other  sources  within,  which  can  not  be  ignored.  We  do  not 
•even  yet  seem  to  be  suflBciently  alive  to  the  delicacy  and  the 
immense  variety  of  our  sensations,  some  of  which  are  abso- 
lutely indefinable ;  otherwise  we  do  not  think  such  experiments 
as  that  above  cited  would  be  adduced  in  proof  of  a  special 
sense  of  equilibrium. 

Qjntil  farther  evidence  is  forthcoming,  then,  we  are  not  in- 
clined to  give  assent  to  the  existence  of  any  mechanism  in  the 
senuciccular  canals,  affording  sensory  data  so  enti/ely  different 
from  those  furnished  by  other  recognized  (and  unrecognized) 
sense-organs,  that  upon  them  alone,  or  in  a  manner  entirely 
their  own,  arises  a  consciousness  of  equilibrium.  We  are  in- 
clined to  regard  the  latter  as  depending  upon  the  fusion  in  con- 
sciousness of  a  vast  complex  of  sensations ;  and  that  upon  the 
whole  being  there  represented,  or  a  portion  wanting,  depends 
either  the  preservation  of  equilibrium,  or  a  partial  or  entire  loss 
of  the  same.  Nevertheless,  it  is  higUy  probable  that  sensory 
impulses  of  a  very  important  character,  in  addition  to  such  as 
are  essential  for  hearing,  may  proceed  from  the  semicircular 
canals,  and  indeed  other  parts  of  the  labyrinth  of  the  ear. 


V 


Forced  Movsmknts. 

When  certain  portions  of  the  brain  of  the  mammal  have 
been  injured,  movements  of  a  special  character  result,  and, 
inasmuch  as  they  aii*e  not  voluntary,  in  the  ordinary  sense  at 
least,  have  been  spoken  of  as  forced  or  compulsory.  The  move- 
ments may  be  classified  according  as  they  are  aroimd  the  long 
vertical  or  the  transverse  axis  of  the  body  of  the  animal.  Hence 
there  are  "  circus  "  movements,  when  the  creature  siiiiply  turns 
about  in  a  circle, "  rolling  "  movements,  etc.  These  and  others 
may  be  toward  or  from  the  side  of  injury.  While  in  some 
cases  there  may  be  a  certain  amount  of  muscular  weakness  in 
consequence  of  the  injury,  which  may,  in  part,  account  for  the 
direction  of  the  movements,  this  is  not  so  in  all  cases;  nor  does 
it,  in  itself,  explain  the  fact  of  their  being  plainly  not  volun- 
taixin  the  usual  sense. 

cThe  parts  of  the  brain,  which,  when  injured,  are  most  liable 
to  be  followed  by  forced  movements  are  the  basal  ganglia  (cor- 


nmiiii  unriiiWiri 


ITTrTTT'- 


»n  experi* 
Lce,  and,  in 
ations,  pos- 
and  many 
We  do  not 
«y  and  the 
ix  are  abeo- 
xperiments 
f  a  special 

are  not  in- 
lism  in  the 
fly  different 
recognized) 
ler  entirely 
We  are  in- 
don  in  con* 
%t  upon  the 
ag,  depends 
r  entire  loss 
liat  sensory 
n  to  such  as 
emicircular 
leear. 


mmal  have 
result,  and, 
iry  sense  at 
The  move- 
nd  the  long 
nal.  Hence 
imply  turns 
)  and  others 
ile  in  stnne 
vreakness  in 
>unt  for  the 
»s;  nor  does 
f  not  volun- 

I  most  liable 
fanglia  (cor- 


THB  BKAIN. 


505 


pora  striata  and  optic  thalami),  the  crura  cerebri,  corpora  quad- 
rigemina,  pons  Varolii,  and  medulla  oblongata,  and  especially 
if  the  section  be  unilateral.  We  have  already  seen  that  several 
of  these  parts  are  concerned  in  muscular  co-ordination ;  hence 
the  disorderly  character  of  any  movements  that  might  now  re- 
sult when  any  part  of  this  related  mechanism  is  thrown  out  of 
gear,  so  to  speak ;  but,  apart  from  that,  we  think  that  the  view 
presented  in  the  previous  sections  is  applicable  in  this  case 
also,  while  the  forced  movements  themselves  throw  light  upon 
the  symptoms  following  injury  to  the  semicircular  canals. 
When  that  constant  afflux  of  sensory  impulses  toward  the 
nervous  centers  is  interfered  with,  as  must  be  the  case  in  such 
sections  as  are  now  referred  to,  it  is  plain  that  the  balance  in 
consciousness  must  be  disturbed ;  confusion  results,  and  it  is 
not  surprising  that,  instead  of  a  passive  condition,  one  marked 
by  disorderly  movements  should  result  in  an  animal,  since 
movement  so  largely  enters  into  its  life-habits.  It  is  important 
to  remember,  in  this  connection,  that  the  great  highway  of  im- 
pulses between  the  cerebral  cortex  and  other  parts  of  the  brain 
and  the  spinal  cord  lies  in  the  very  parts  of  the  encephalon  we 
are  now  considering.  ■ 

Functions  or  thb  Ckrebbal  Convolutions. 

Coaparatif. — It  will  conduce  to  the  comprehension  of  this 
subject  if  some  reference  be  now  made  to  the  development  of 
the  brain  in  the  different  groups  of  the  animal  kingdom. 

(^vertebrates  not  only  have  no  cerebrum,  but  no  brain  in 
the  strict  sense  of  the  term  as  applied  to  the  higher  mammals. 
In  most  forms  of  this  great  subdivisicm  of  the  animal  kingdom, 
the  first  or  head  segment  is  provided  with  ganglia  arranged  in 
the  form  of  a  collar  around  the  oesophagus,  by  means  of  com- 
missural nerve  connections;  so  that  the  nervous  supply  of  the 
head  is  not  widely  different  from  that  of  the  other  segments 
of  the  body.  But  as  we  ascend  in  the  scale  among  the  in- 
vertebrates these  ganglia  become  more  crowded  together,  and 
so  resemble  the  vertebrate  brain  with  its  massed  ganglia  and 
numerous  connections  through  nerve-fibers,  etc.  But  in  this 
respect  we  find  great  difference  among  vertebrates.  We  can 
recognize,  on  passing  upward  from  the  Amphioxua,  destitute 
of  a  brain  proper,  to  man,  all  gradations  in  the  form,  relative 
sizgt  multiplicity  of  connecting  ties,  etc. 

/Speaking  generally,  there  is  great  difference  in  the  weight 


; 


:WtK|iMiti>Bi.tliWWlMl 


iwtiitiiWfltrtiiit 


utmmmm 


mmmimmi 


606 


ANIMAL  PHTSIOLOGT. 


fta.  351. 


Fw.  aw.— NerroiN  urt^m  ot  madlciiMl  Iceoh  (•fter  Ow««).  a,  double  mpr«>oempliMMl 
ipuiSliaa  comiected  wttb  mdimenUuT  ocelli  (6, 6)  by  nervet ;  c,  double  iiifnMMoplMaedl 
gMiglioaic  niMB,  wfaidi  In  conUimous  with  double  ventnl  oora,  IWTiiiir  oompound  nnsilft 
•t  NNter  Interrala 

Fia.  «U.-}fenroai  qratem  of  the  oominon  muMel  (after  Owen).  I,  labial  ganglia  ooonected 
by  a  ahort  conunlMiM above  and  in  fMnt  o?  moi^ ;  b,b,  branchial  ganBla,  eanaectwl 
in  Uke  maiuHr,  and  united  by  tour  aervoue  ooMto  M.  d)  wUh  labial  ganiRla :  »,  Ulobed 
pedal  ganglion  aendiiw  braaehea  to  the  muscular  foot  (r),  and  cloaely  unlMwith  the 
"auditorr  laoailea"  Q) :  h,  h',  drcum-paliial  plexua;  y,  byaras,  by  which  the  animal 
can  attach  ilaelt  to  fofaiiEa  bodtea  (anchor) 


of  the  cerebrum,  both  relative  and  absolute.  In  all  animals  be- 
low the  primates  (man  and  the  apes)  the  cerebellum  is  either 
not  at  all  or  but  imperfectly  covered  by  the  cerebrum ;  while 
in  man,  so  great  is  the  relative  size  of  the  latter,  that  the^ 
cerebellum  is  scarcely  visible  from  above.  If  we  ex(;ept  the 
elephant,  in  which  the  brain  may  reach  the  weight  of  ten 
pounds,  and  the  whale  with  its  brain  of  more  than  five  pounds 
in  the  largest  specimens,  the  brain  of  man  is  even  absolutely 
heavier  than  that  of  any  other  animal,  which  is  in  great  part 
due  to  the  preponderating  development  of  the  cerebrum. 

While  the  cerebral  surface  is  smooth  in  all  the  lower  verte- 
brates, and  but  little  convoluted  imtil  the  higher  mammals  are 


^ai^iii  ..ji.  I  J  ^1 1 


t^Atlltfl  iiil1ltfai.»i^ii»ii^^Wil>i'**<lW-^ 


ml 

Mnpoand  gangilft 

an^rtU  oomwcted 

IBBBA,  OOBlMOted 


.ngiW ;  p,  I 

'  unltcdwith  the 


animals  be- 
im  is  either 
rum;  while 
)r,  that  the'^ 
except  the 
Ight  of  ten 
five  pounds 
I  absolutely 
1  great  part 
>rum. 

lower  verte- 
ammals  are 


rf.    .■■'" 


Tin.  '< 


THE  BBAIN. 


m 


I 


Fta.1 


rn.  854. 


na.aB6w 


Fra.  aw.-ir«r*oas  vyrtem  of  *  wklte  ant,  IWihm  'tttet  QeKenbMir  and  Lemte). 

S**  g»--SywM  *y*em  of  a  water  beHle,  ZMUIbum  (after  Gegenbaur)/^ 

"*•  ■»••— Herwwi  mtem  of  a  fljr,  JAiaea  (after  Gteeenbaur  and  Blandiard).    o.  eyee ;  <m, 

■m»«BMi|ilM«eal  gaagUa  or  brain ;  gi,  ■ub-<BW>plM«eal  gangUon ;  gr,  gr*,  gr*,  tvaSd 
_„  Mowcw  janulla. 
'"••J5sr";P'2??*wB?*ffi  **  A  orah.  IWiHurtif  tmlga,  ..i,  A/awtng  considerable  ttuion  ot 

faniga  (after  Mtfne-Mwarda).   a,  ftiMd  oereliral  ganc^ ;  b.^W  oMnplWKeal  corda ; 

<n&  great  ventral  mw^lonic  maw.  »—»...  -•        i—» 


P'-IK*,  fleet 


I  gan^ia ;  i,  great  Tentral  ganglion ;  o,  «yea ;  p,  paqii; 


-■-  mmnae. 


508 


ANIMAL  PHTSIOLUGT. 


^ 


Fio.  W.— Nmtoub  _, 
■uprxwwiilMgB*' 

and  month;  n^tB, 
tanmerrcs. 


of  commOB  cottto-Mi,  9»ta  ^/teinalia  (after  CHren).    1.  <Jo«W» 

tUoB ;  p,  p,  cut  MirfMM  of  the  canUaKinous  cnuilum ;  8J,  optJo 

nb^MOfihaaeal  Kaiwiia ;  7, 8,  gaM^taTn  connection  with  pharrnz 

niotor  ner»w  of  mantle,  eic^  with  other  ganglia ;  14.  c,  c,  rejjara- 

of  thto  animal  it  in  pfoportiaa  to  the  iiae  and  concentration 


Vm.  aga-Bralnand  cranial  nenrea  of  pen*,  iMnfWm  tte  aideCaftar  OMenbrarand  Cwtcr)- 
Xoerebral  lobe  with  olfactomnKtlion  to  flfont ;  B,  optte  k*e :  ft  cweh^um :  £^me• 
dnila  obkmgata;  I-Vm,  ner^  bi  usual  order  ;Jr,  lateral  bnnofa  <^  »■«»«•  L**  "W*' 
tSSTof  S^r  m.  dorwl  braw*  0*  WgemtaiB,  Jotoed  by  1^^ 
OK  y ,  ^w  bnndMa  of  trlc«nhnM ;  It,  facial  nerve ;  A,  brandiial  bruidtoa  o(  v^^ 


ran).  1,  double 
ium;  8,8,  optic 
n  with  pharynx 
14,e,e,rMpira- 
A  oonoentratlon 


«ar  and  Caller), 
ebelhim:  i>,  me- 
Tanw:  t,  nppw 
nwdi  of  TBgua; 
shMoCvagw. 


THE  BRAIN. 


60» 


reached,  the  brain  of  the  primates,  and  especially  of  man,  has 
its  surface  enormously  increased,  owing  tu  its  numerous  fis- 
sures and  convolutions,  which,  in  fact,  arise  from  the  growth 
of  the  organ  being  out  of  proportion  to  that  of  the  bony  case 
in  which  it  is  contained;  and  since  those  cells  which  go  to 


'^^-"^iiiMrt^W^   t 


9       '<&'- 


Fia.  880.— Brain  and  apinal  cord  of  frog  (Bastian).  A,  otfactory  lobe* ;  B,  cerebral  lobeR ; 
R,  pineal  body ;  C,  D,  optic  lobes ;  E,  oerebeUum ;  U,  ■pinal  oord.  The  cerebelluin  la 
notably  amall. 

make  up  the  gray  matter  and  are  devoted  to  the  highest  func- 
tions, are  disposed  over  the  surface,  the  importance  of  the  fact 
in  accounting  for  the  su^ierior  intelligence  of  the  primates, 
and  especially  of  man,  be  jmes  apparent.  Depth  of  Assuring 
is,  however,  of  more  importance  than  aultiplicity  of  furrows ; 
and  it  may  be  observed  that  in*:  HigCire  is  not  always  in  pro- 
portion to  the  extent  to  which  the  cerebral  surface  is  broken 


7M.M1. 


FM.  SM). 


'POm  above  (Huxley).    A,  tbe  olfactory  nerves  or  lobM, 
'•jtt ;  B,  the  cerebral  nemi*id>erea :  C,  the  optic  loban    D, 


Flo.  MO.— Bratai  of  the  pike.  *<*>■ 

and  beneath  thnn  the  optic  ■ 

the  cerebdium. 
Fio.  881.— Tbe  bitain  of  edible  frotr  (Antia  ewMieafa).    1x4.    (Afen-  Huxley.)    L.  ol.  the 

riilnenaephalan,  or  olfaotory  lobea,  with  /.  the  olfactory  nerves  :  He,  tbe  cerebral  henrf 

Bpheree :  Fk.  o,  the  thalamenoeidialon  with  the  pineal  riand,  Ph  ;  L.  op.  optic  lobea ;  C, 

oerebeUum ;  a.rk,thr  i'oiuth  ventricle ;  3to,  medulla  oblongata. 

np  into  fisexr  ;S  iud  convolutions.  The  depth  of  the  gray  mat- 
ter is  also  very  wriable,  and  seems  to  betur  an  important  rela- 
tion to  psychic  development.  Man's  brain,  then,  is  character- 
ized by  its  great  size  and  oomplezity ;  while  those  parts  treated 


l 


i 


Bwa.'4t;-aw-'.jj.>jjjk..asj.jiiiMiiiiiiHMia«ai 


»tta'.'juuttw»'miiJj,<!M'.'«ijii«jistwj|i>ijM.>i.;^^^ 


SB 


ftlO 


ANIMAL  PHYSIOLOGY. 


^^ 


Fio.  an-Braiim  of  »  Miard  (PaammomurM*  B^mgalmMi  mdofa  bM  (JMM«:ito  mOiifMm) 
ItilMiaitiMUiid and Tertical  Motion.  The upMr  fl«ii«  rMpnMnts  tte  UwirdHi  brain ;  the 
towSfttSTof  Th«  bird  (■««•  Hwdey  andTSnilB.  !««««  ■•  to  the  PNW^  ttawcj 
orawtTl,  lanUtia  (erminaUf,  or  uWlor  widl  of  Oie  tiiird  Tentrioio ;  /.  U,  fonunenof 

teriarmmDiiMUN ;  <« JndioitfM  tha  enot  noint  of  exit  of  the  (omrth  piUr  from  Uwt  put 
of  Mm  brain  whiA  anairan  to  the  tahw  of  ViMMMna. 


ft-  ^  j'iv^^ntifntfH^trn^anitiiivr  rt»i»> 


- -*-«h«e«?w«»*rt«iiift" : 


ea 


»bifd(ifcfea- 
Iwtiey).  A,  B, 
ninMU  Klsnd; 
ib^um ;  JM>, 
A  mttm;  Pu, 


ir.a 


\Ori$aaaopatia) 
jrdHi  bnUn ;  tbe 
teovMait  flgwp, 
.  jr,  f  onunea  of 
ntomre :  p,  pot- 
(ram  Uwt  iMTt 


THE  BRAIN. 


611 


Fw.  SM. 


Fto.  aUB. 


Fia.  sat. 


F10.8M.— Brain  of  ptaeoD  (afler  Ferrler).  A,  cerebral  hwnl^iliew ;  B,  optfas  lobe ;  C,  cere- 
bellum, the  Ikteriulobes  of  which  are  Teiy  nulL 

Fio.  886.— Brain  and  q>inal  cord  of  chick  at  aizteen  dagra  old ;  optic  lobea,  6,  are  bUU  in  con- 
tact (after  Owm  and  Andennn). 

Flo.  aw.— Brain  and  iMUt  of  apinal  cord  of  chick  twenty  daja  old,  Bhowlmr  optic  lobes  widely 
■eparated  and  cerefaellum,  e,  largely  devekqped. 

elsewhere,  concerned  in  co-ordination,  vision,  etc.,  are  well 
developed,  the  cerebrum,  especially  its  lobes  as  distinguished 
from  its  basal  ganglia,  is,  out  of  all  proportion,  greater  than 
in  any  other  animaL 


Vnl>  808> 


Ho.  aor.— Outer  rarfaoe  of  brain  of  bone  (after  BoDy  and  Leuret).  «.  otftatonr  lobe :  ft,  hip- 
pocampal  lobe  (procMm  pyrtformto) :  1,  S.  8,  lobes  of  cerebeUum ;  o.  <mtic  nenre ;  m, 
motor  oouU :  p,  Ararth  nerre ;  (,  flfth  n«nw ;  it,  sixth  nerve ;  f,  facial ;  1,  auditory ;  g, 
^osso-nhanrnM^ :  v,  tmus  :  «,  i^tal  Moeaaonr :  n,  hvpoRloaaal :  X.  pons  VarpUL 

Fio.  atS.— LonMtudinal  section  tttrough  center  of  twain  of  horse,  presenting  view  of  Internal 
Bwrfaoe  (after  Solly  and  Leuret).  c.e.  corpus  caUosum ;  p,  thalannis;  m,  middle  eom- 
miasure ;  f.o.  °'>''^*||^  wwdrigemina,  In  front  of  which  Is  the  ptosal  body.   The  osrebel- 


"'''«»BMav<,<lit.uWj:Uii|,L.iiHa,aM.BUii|iiMt|paijti^^^ 


^ 


6ia 


ANIMAL  PHYSIOLOGY. 


The  gray  matter  of  the  brains  of  the  higher  vertebrates  is 
distributed  as  masses  of  ganglionic  cells  internally,  and  as  a 
fairly  uniform  layer  over  its  surface.    The  cerebrum  of  man 


no.  aao.— Lateral Ttewt of  tliB  hnU—of  >rrt»hit,»  plg.—d  a  ohlmpiMW.  dmwnof  iwriy 
tiMMunealMOlutoaiaeCHiizlMF).  Tlw  rabMt%  iMta  to  at  the  tdpttlWBl(*i,te  the  middle: 
the  cMmpUMel.  loweat   Oi;ollMtoi7MMS  ikfKWtal  lolw)  B.ocetoMl^^ 


'.F  itr  I.F 
inperior,  midaie,  Mul  inteior  fronUI  nri  ',A.P,  .iurterpiNulital ;  P.  P.  DortWwviigtai 
Kyri;  i;,mloueof8olMM;  1>. i>t. |M)«Mro>|»rletaI  lobule ;  O. flT. extenufl perpgidleiily 
oroodpito-temporalndoae:  ^n,  aiiRatar  gms :  B,  S,  4,  MUMteiit  gyri ;  .i.  T,  If.  T,  P.  r, 
thethiwitemparal,Mid  AOe,JilOe^/.oOKethiwoool|ittdKM 

weighs  about  three  pounds  on  the  average,  that  of  the  male 
being  a  few  ounces  (f otir  to  six)  heavier  than  that  of  the  female. 
The  individual  and  race  differences,  though  considerable,  ar<) 


^^'wnkiiipaBiimifwitiM 


iilii  iM  iJg^iiMllWMMiMM 


bebrates  is 
,  and  as  a 
m  of  man 


« 


bwinior  nearly 
I,  In  the  middle; 
itlobe:  atem- 
paanra-paratal 
11  perpandlonlar 


I  the  male 
bhe  female, 
erable,  am 


THE  BRAIN. 


518 


not  comparable  in  degree  to  those  that  distinguish  man  from 
even  the  highest  apes,  the  br^  of  the  latter  weighing  not 
5??ro  ^^^  ^^*'  one  third  as  muchaslEat  of  the  KimanTsub-, 
jsct  While  it  has  been  showii  that  indtvidtisllnen  and  women 
may  reach  even  distinction  in  the  intellectual  world,  having 


'^'•1^'°^^'^^  ombral  hwilnlietMaf  the  nUMt,  itg.nA  cUmMikMe. drawn m 

6^^SSl^ Sn^SS^'  ^  W|iI?H»iBjDrfwloS;  c;M.aiioliwte;  Jf.  miuBiSu  cTS- 
loi«l  gyH ; /. /►  totonial  l«rpeiidlcntar ;  fl5r«aoMrtoe ;  *l^ 

brains  of  average  or  even  sub-medium  weight ;  and  while  idiots 
have  been  known  to  possess  brains  abnormally  heavy,  it  is( 
nevertheless  true  that  bndn-weight  and  thfe  higher  powers  of 
man  bear  a  close  though  not  invariable  relationship.     The 
apparent  discrepancies  are  susceptible  of  explanation. 


HMMMtUimte; 


614 


ANIMAL  PHYSIOLOGY. 
I 


> 


CM. 


Ami. 


Tm.  K\.-Vnin  of  diimpMiMe,  put  of  right  beniiplMre  being  cut  vnj  w  m  to  axpoM 
Tto^'^fSSS^i^^SiS^^^rb^^.ri.l.  b'-5.«»ofttie««ll«teT«r 

mslor  in  dMoSStag  •ornu;  fcrn.  WwooMnpujmlnor  taportartorcorou  j/l^  ^nri 

Sitamid  pMTMdkmter  Amuni  :  Jcropercuium :  I,  A,  mommUiic  tronUI ;  B,  B.  Moending 
parM«l  ooBfolatloii. 


MWMWaJMHMWIJ'IIIWIWMM'W**'''!' 


1 


ff» 


ct. 


-Am, 


ly  WM  toaxpoM 

(  the  nMllMt  erer 
wtween  theM  two 
:  CO.  hlppoaunpiw 

i;B,B.  aaoending 


filfi 


JJo.  sn.— n«ln  of  onuif ,  ride  view  (after  Vogt  and  Gntiolet). " 

Vm.  8T4.— Bntai  of  •  Hottastot  woman. 

""'nnr'^*'^  *^^<%!!?*  **>"  celebrated  mathematioian  and  artronomer  (an«r  Vogt  and 
fta'tifSSSL JS^£SSf'*JteSi*5"  tW«  tart. bnUn  and  the  two  flHTiiiS^ ?Sl ^ 
^iS^^^^^SSL^^SfhS!.!  ^'^.  J*"^  f~  Intended  to  Uluftrate  racial  and  IndtTMuat 
^erenoea  on  the  one  hand,  and  the  greater  reaemblanoe  to  lower  forme  of  the  brain  of 
the  more  degraded  raoee  of  men. 


!1 


iA» 


iiiiriUiHiili<jiuiiu»iNi],iiiiii,iii]inj; 


516 


ANIMAL  PHYSIOLOGY. 


i 


mmmmMmimmMmiimitt^tnmi- 


Hcrawt).   1,  Miper- 
^dU  oel]fc;4,layer 


THE  BRAIN. 


517 


Besides  the  gray  matter,  with  its  cells  of  highest  functional 
value  from  the  standpoint  now  taken,  the  brain  consists,  and 
in  large  part,  of  neuroglia  and  nerve-fibers,  with  probably 


Ha.  877.— UagrwmiMtlo  horlimital  Mctioa  of  a  vertebrate  brain  (Hozlnr).  The  foUowinc 
MttersMrve  for  both  this  flsure  and  tiw  one  foltowliiK.  Jfb,  mid-brain.  What  Uw  in  froS 
of  tliisjs  llie  f ore-braiiLand  what  lie*  behind,  the  Und-brain.  L.  t,  the  lamina  terminalia ; 
W,  <^actorr Jobea ;  Amp,  hemiq;therai ;  3%.  K,  Hialamenoeirtiakm :  P*,  pineal  sland ; 
Ar,  pituitary  body ;  FJT, foramen  of  Mnnro;  C&  oorpua  etriatnm ;  7%, opOe  thalamus ; 
^"Jf*??  qinAigw^ ;  CO,  mnaoarebri ;  C6.  oerebelhmi ;  PV,  pona  Varolii ;  MO, 
medullaoUpogata :  £  oltaetorii : //,  optici ; /J7,  Mtatt  of  exit  from  bndn  of  motoies  oculo- 
nm:/r,of  paOett^:  FAofalMhieealea;  F-XaTorlsiaa  of  the  otter  eenbral  nenca. 
*'!*?P*°*T^«P^'«*i«..^*wy'*»"*rtel»;l.aartTOrtrlcie;4.foii^  *,iUr 

a  (erHo  od  ffMortHM  MiMrieHiMM. 


Via.  878.— A JpnffltDdlnal  and  vertleai  eectiMi  of  a  vertebrate  brain  (Huxlar).   Letten  aa 
above.    The  temAMtemOiiaUi  la  npreaented  by  the  etrong  Mack  Une  between  FJf  and  8. 

chiefly,  and  in  the  case  of  the  fibers  solely,  a  conducting  func- 
tion. It  will  appear  that  body-weight  must  be  taken  into 
aocotmt  in  comparing  the  brains  of  the  sexes  and  of  indi- 
viduals.   Again,  the  quality  or  functional  capacity  of  the  iudi- 


'>^'^m 


.:  < 


■'^^<**»*'*^^iiilU!miB!»KifmiimtaiaiiviiK^siiiK 


?'  IS- 
:;  if 


518 


ANIMAL  PHYSIOLOGY. 


vidual  elements,  especially  of  the  cortical  cells,  both  as  the  re- 
suit  of  innate,  inherited  powers,  and  as  altered  by  education, 
is,  of  course,  a  matter  of  great  importance.    By  education  we 
m@an  all  those  influences  that  have  been  brought  to  bear  upon 
these  cells  from  without,  of  whatever  kind.    Apart,  too,  from 
all  these  considerations,  it  must  be  clear  that  what  any  set  of 
cells  can  accomplish,  be  they  brain-cells  or  other,  must  depend 
largely  upon  their  capacity  to  appropriate  nourishment,  which 
will  in  turn  be  modified  by  blood-supply,  the  behavior  of  ex- 
creting organs,  etc.    In  a  word,  the  intellectual  achievements 
are  dependent  on  a  great  variety  of  factors.    The  brain  and 
other  parts  are  so  mutually  dependent  that  they  can  not  be  un- 
derstood by  any  isolated  consideration  of  the  one  or  the  other.N 
It  is  not  to  be  supposed  that  an  individual  with  a  poor  respir- ) 
atory,  circulatory,  and  digestive  system,  no  matter  what  the  ' 
possibilities  of  his  cerebrum,  can  ever  rank  with  an  organism ' 
admirably  balanced  in  these  respecta 

The  Oonneetion  of  m»  Part  of  tho  Bndn  with  aaotlior.— Though 
it  has  long  been  known  that  the  different  parts  of  the  brain 
were  connected  by  bridges  of  fibers  {commissures,  etc.),  the 
physiological  significance  of  the  fact  seems  to  have  been  largely 
ignored,  and  even  at  the  present  day  is  too  little  considered. 
1.  Cerebral  fibers  pass  between  the  convolutions  of  this  part  of 
the  brain  and  the  cerebellum ;  between  the  former  and  the  main 
basal  ganglia ;  between  the  gray  matter  of  the  convolutions  on 
the  same  side,  and  between  the  latter  and  those  on  the  opposite 
halves ;  between  the  gray  matter  of  the  cortex  and  the  internal 
capsule,  the  corpora  striata,  optic  thalami,  pons  Varolii,  the 
medulla  oblongata,  and  so  to  the  spinal  cord.  The  course  of 
the  latter  tracts  of  fibers  have  been,  especially  by  the  help  of 
pathology,  definitely  followed.  Some  of  these  connections  are 
given  in  more  detail  below :         • 

1.  Cerebro-cerdteUar  fibers,  (a.)  From  the  cortical  cells  of 
the  anterior  cerebral  lobe  to  the  pons  Varolii,  passing  through 
the  internal  capsule  and  thence  through  the  lower  and  outer 
part  of  the  eras  cerebri  {crusta),  (6.)  Fibers  from  the  occipital 
and  temporo-sphenoidal  lobes,  passing  by  the  crusta,  reach  the 
upper  surface  of  the  cerebellum. 

2.  Fibers  bridging  the  two  sides  of  the  cerebrum,  (a.)  By 
means  of  the  corpus  callosum  chiefly,  passing  from  the  gray 
matter  in  the  first  instance.  (&.)  From  the  temporo-sphenoidal 
lobe  on  each  side  through  the  corpora  striata  and  anterior  com- 
missure,   (c.)  Fibers  from  the  upper  part  of  the  crus  cerebri 


■-.;AftW»Wl>#_iWJ,l.|UM«<MJ4««.»WJMI'''M'WiJIJ'»IMU»IM»»iluCMII««ll»U 


iMMRiiiVW-Wla 


iiw  the  re- 
education, 
ucation  we 
bear  upon 
t,  too,  from 

any  set  of 
lUst  depend 
lent,  which 
ivior  of  ex- 
hievements 

brain  and 
I  not  be  un- 
p  the  other.N 
poor  respir- 
r  what  the 
,n  organism . 

».— Though 
f  the  brain 
»,  etc.),  the 
leen  largely 
considered, 
this  part  of 
ad  the  main 
rolutions  on 
;he  opposite 
the  internal 
Varolii,  the 
le  course  of 
the  help  of 
lections  are 

ical  cells  of 
ng  through 
»r  and  outer 
he  occipital 
reach  the 

m.  (a.)  By 
im  the  gray 
HBphenoidal 
iterior  com- 
srus  cerebri 


THE  BRAIN. 


510 


{tsgmentum)  to  the  optic  thalamus  of  each  side  and  onward 
to  the  temporo-sphenoidal  lobes,  forming  the  posterior  oommis* 
sure. 

3.  Fibers  connecting  different  parts  of  the  cerebral  convolu- 
tions on  the  same  side.  These  are  exceedingly  numerous  and 
are  effected  by  such  tracts  as  the  "arcuate  fibers,"  passing  from 
one  gyrus  to  another ;  "  collateral  fibers,"  forming  distant  convo- 
lutions ;  fibers  of  the  fornix  between  the  uncinate  gyrus,  hip- 
pocampus major,  and  optic  thalamus ;  longitudinal  fibers  of  the 
corpus  callosum;  fibers  of  the  taenia  semicircularis,  uncinate 
fasciculus,  etc. 

4.  Fibers  forming  the  cerebrum  and  the  spinal  cord.  Ac- 
cording as  they  pass  downward  or  upward  do  they  converge  or 
diverge,  and  the  most  important  seem  to  pass  through  the  in- 
ternal capsule ;  and  while  the  majority  do  perhaps  form  some 
connection,  either  with  the  corpora  s^ata  and  optic  thalami. 


As.  »«.-I>iagnHUiwtlc  repratenution  of  the  ooune  of  mne  of  the  flbera  in  the  cerebrum 

(Itfter  Le  Bon). 


wiiiyffiwtW)B«ibj.ifiwi:*www>a>wiw4'iitwiMwu'aiM^ 


WJuiWMHBk.tftlft*»*l 


K**am^m»iiiiaMi(Lvte9teim  i-^^f 


;ftt 


■''i 


590 


ANIMAL  PnrSlOLOOY. 


some  seem  to  pass  directly  downward  through  the  internal  cap- 
sule. It  is  held  by  many  that  the  fibers  passing  through  the 
posterior  portion  of  the  ii)temal  capsule  are  derived  from  the 
posterior  lobe  of  the  cerebrum,  and  are  the  paths  of  sensory  im- 
pulses upward ;  while  the  rest  of  the  internal  capsule  is  made 
up  of  fibers  from  the  anterior,  and  especially  the  middle  portion 
of  the  cerebral  cortex  (motor  area),  and  these  fibers  are  the 
paths  of  motor  (e£ferent)  impulses. 

Ot  now  becomes  clearer  that  the  brain  is  constituted  a  whole 
by  such  connections ;  and  that,  apart  from  the  multiplicity  of 
cells  with  different  functions  to  perform,  situated  in  different 
areas,  the  complexity  and  at  the  same  time  the  unity  of  the 
encephalon  becomes  increasingly  evident,  merely  upon  anatomi- 
cal grounds ;  but  we  shall  find  such  a  view  still  further  strength- 
ened by  study  of  the  functions  of  the  various  parts.  While  the 
tracts  enumerated  are  anatomical  and  have  been  clearly  traced, 
there  can  be  little  doubt  that  many  others  yet  remain  to  be 


»W I CTA u 


CAUOIO-MARSniAL 


■CPTUM 
LUCI 


FISSURCOmOLANDe 


ArrcNwi  

coMMistuM        Munivr 

MrUNDiWU 


•PTKTHALAMUC 

KHCRVI  ' 
AOUtDUCTOrsnMUS.' 

nNEALfiUlK:' 
CORPORA  OlMORIttMINA' 


TRAMSVIRSC 
nSSURC 


VALVC 
or  VICUStENt 

4n  vnrrmctx 


no.  an.— Median  laaghwUiial  wction  of  human  brain,  ■wnt-dlagraininaHe  (attar  FUnt). 

marked  out ;  and  that,  apart  from  such  collections  of  fibers,  we 
must  recognize  functional  paths  by  the  neuroglia,  and  possibly 


'^"*«vnfe«iM|MiiH 


internal  cap- 
through  the 
ed  from  the 
f  sensory  im- 
Mule  is  made 
iddle  portion 
bers  are  the 

;uted  a  whole 
ultiplicity  of 
I  in  different 
unity  of  the 
pon  anatomi- 
;her  strength- 
i.  While  the 
ilearly  traced, 
remain  to  be 

SURCOFROlAMDe 


kCALCARINC 
1  FIttUM 


rriMMSVimc 
nssuRC 


'  VALVE 
or  VIEUStENt 

'4"  vnrrmcu 


natic  (•ftcr  Flint). 

L8  of  fibers,  we 
k,  and  possibly 


THE  BRAIN. 


591 


others  still.  It  is  not  to  be  forgotten  that  in  the  brain,  as  in  the 
spinal  cord,  nerve-cells  are  themselves  conductors,  and  while 
there  may  be  certain  areas  within  which  the  resistance  is  such 
that  impulses  are  usually  confined  to  them,  it  is  also  true  that, 
as  in  the  cord,  there  may  be  a  kind  of  overfiow.  Adjacent  colls, 
possibly  widely  separated  cells,  may  become  involved.  We  shall 
return  to  this  important  subject  again,  however,  as,  without 
recognizing  such  relationships,  it  seems  to  us  quite  impossible 
to  understand  the  facts  as  we  find  them  in  the  working  of  the 
body  and  the  mind. 

The  Gwebral  Cortex.— We  may  now  proceed  to  inquire  what 
are  the  functions  of  the  c^  of  the  gray  matter  covering  the 
surface  of  the  cerebrum,  (before  the  birth  of  physiology  as  a 
science^allj  recognized  and  taught  that  the  encephalon  is  a  col- 


'^nSl^S^SSSMrBSEST'***^ 


lection  of  organs ;  that  these  have  separate  functions ;  that  the 
relative  size  of  each  determines  the  degree  of  its  functional  ac- 
tivity;  and  that  the  cranium  developing  in  proportion  to  the 
growth  of  the  brain,  the  former  might  give  information  as  to 
the  probable  size  of  what  lay  beneath  it  in  different  regions. 


n-sMBitmmmK/cr'- 


•  ■-TTt*ff.t^rt»a®«*Wr  V , . 


&2S 


ANIMAL  PHISJ^/ 


'V. 


It  will  be  seen  that,  a»  thus  inter,  'A,  phrenology  is  a  very 
different  thing  from  what  usually  passes  under  +hat  name,  and 
is  paraded  before  wondering  audiences  by  ignorant  charlatans. 
In  the  main  the  doctrines  of  fOall^  are  not  without  a  certain! 
foundation  in  facts ;  and  the  modem  theory  of  localization  of' 
function  bears  a  strong  resemblance  to  what  Qall  taughty 
though  with  greater  limitations. 


ftam"*** 


Wn.  981— Diamuninatio  rapreMnUtkm  of  internal  mrfaoe  of  rMit  oerrtml  hemtophere,  aa 
aeen  in  vemcal  longituduial  mndiMi  aeotioii  (after  Flint  and  Ecker). 

/Among  the  more  modern  observers, ||Touren8/held  that  re- 
moval of  small  portions  of  the  cerebral  cortex  produced  no 
effect  on  either  will-power  or  intelligence,  but  that  if  carried 
far  enough  both  volition  and  intelligence  were  completely  de- 
stroyed. Later  observers,  say,  of  ten  years  ago,  maintained 
that  the  whole  or  the  greater  part  of  the  cerebral  cortex  might 
be  mapped  out  into  areas  with  a  definite  function.  The  meth- 
ods of  investigation  have  been  clinico-pathological  and  physio- 
logical. 

It  was  found  that,  on  stimulating  certain  areas  of  the  cortex 
(e.  g.,  the  so-called  motor  area),  certain  movements  followed, 
but  that  similar  results  were  obtained  when  the  f)lectrodes  were 
applied  directly  to  the  white  matter  underlying  the  cortex; 
hence  the  results  of  such  experiments  were  not  conclusive.  It 
was  held  that,  if  certain  regions  thus  respondent  to  a  stimulus 
were  removed,  the  movements  of  corresponding  muscles  should 
be  abolished ;  in  other  words,  there  should  be  localized  paraly* 


>tiilijiifw»jiy!Sjaw!tPWii^^f:ww»w«w^ 


nlM 


gy  18  a  very 
A  name,  and 
,  charlatans, 
lit  a  certain] 
;alization  of 
}all  taugbty 


ral  hemisphere,  as 

leld  that  re- 
produced no 
At  if  carried 
mpletely  de- 
maintained 
x>rtex  might 
Themeth- 
and  physio- 

of  the  cortex 
its  followed, 
tetrodes  were 
the  cortex; 
nclusive.  It 
K>  a  stimulus 
iscles  should 
lized  paraly- 


THE  BRAIN. 


528 


sis.    It  was  then  asserted  by  certain  experimenters  that  such 
was  the  case,  while  others  strenuously  denied  this.    By  com- 


na.  88S.— Outer  Murfaoe  of  oerebrum  (after  Elzner).  The  shaded  portion  representii  Me  motor 
in  man  and  the  monkey— i.  e.,  the  area  which  moat  observers  MieTe  to  be  associated  with 
certain  Toluntair  moreinents  of  the  limbs,  etc. 

bining  the  method  of  stimulation  with  that  of  ablation  (or  the 
removal  of  definite  portions  of  the  cortex),  a  very  extensive 
localization  was  established  by  certain  observers  (Hitzig,  Fer- 
rier,  etc.).  This  was  not  confined  to  motor  functions,  but  in- 
volved sensory  ones. 

rOn  the  other  hand,  one  physiologist  ((<&oltz][Jias  from  the 
first  maintained,  as  the  result  of  experiments  on  the  dog,  that 
localization  of  the  character  described  by  the  above-mentioned 
observers  does  not  exist.  He  finds  that  no  amount  of  ablation 
of  the  cerebrum  will  lead  to  paralysis,  and  that,  if  lesions  in 
any  part  bebut  extensive  enough,  the  sensory  perceptions  and 
the  intelligence  of  the  animal  aro  impaired.  It  is  found  that 
the  movements  of  dogs,  after  the  removal  of  a  considerable  por- 
tion of  the  cerebral  cortex  are  awkward ;  that  one  or  all  of  the 
animal's  sensory  perceptions  may  be  impaired ;  that,  in  fact, 
the  creature  may  be  reduced  to  a  mere  eating  and  drinking 
machine,  as  it  were ;  but  that  paralysis  proper  does  not  exist. 


(I 


k 


624  ANIMAL  PHYSIOLOGY. 

'  About  the  same  time  another  experimenter  (Munk)  had 
been  attempting  to  map  out  the  region  of  the  cortex  concerned 
in  vision.  As  a  result  of  removal  of  different  portions  of  the 
occipital  lobe  in  dogs,  he  had  concluded  that  a  portion  of  this 
lobe  constituted  the  cortical  visual  center,  and,  further,  that 
the  blindness  resulting  from  such  operations  as  are  now  under 
consideration  was  either  "  absolute  "  or  "  psychical " ;  by  which 
was  meant,  in  the  first  instance,  an  inability  to  bring  the  images 
of  the  retina  into  consciousness,  and,  in  the  second,  inability  to 
interpret  visual  sensations  intelligently,  the  one  or  the  other 
result  being  dependent  on  the  part  of  the  limited  visual  center 
that  was  removed.  This  may  be  regarded  as  perhaps  the  most 
extreme  form  of  sensory  localization  yet  taught. 

(^oltz,  as  a  result  of  his  latest  experiments,  not  only  denies 
that  operations  ou  the  occipital  lobe  are  peculiar  in  producing 
visual  disturbances,  but  points  out  that  these  lead  to  sensory 
defects  overlooked  by  Munk.  This  observer  (Goltz),  as  a  result 
of  comparing  a  dog,  with  both  anterior  cerebral  lobes  removed, 
with  others  from  which  were  removed,  in  the  one  case,  the 
right,  and  in  the  other  the  left  corresponding  parts  (anterior 
cerebral  lobec^,  since  he  finds  the  dog  with  both  removed  in  a 
worse  condition  than  would  be  represented  by  the  joint  result 
of  the  addition  of  the  imperfections  of  the  other  two,  concludes 
that  one  cerebral  lobe  may,  to  a  certain  extent,  take  up  the 
functions  of  another.  In  other  words,  he  admite  localization 
but  only  of  the  roughest  kind. 

A  view  advanced  by(ScJiiff  deserves  probably  more  consid- 
eration than  it  has  received,  viz.,  that  motor  areas  are  so  related 
to  tactile  sensations  arising  in  different  parts  of  the  body  that 
when  the  former  are  stimulated  the  resulting  movements  are 
really  reflex — i.  e.,  the  stimulation  of  the  cortex  replaces  the 
afferent  sensory  impulses,  which  usually  are  associated  with 
the  movements  in  question. 

In  the  mean  time  it  has  been  found  that  in  many  cases  it 
was  possible  to  locate  the  site  of  a  brain-lesion  (tumor,  etc.)  by 
the  symptoms,  chiefly  motor,  of  the  patient ;  and  brain-surgery 
has  in  consequence  entered  upon  a  new  era  of  development. 
Tumors  thus  localized  have  been  removed  sucoessfully,  and  the 
patients  restored  to  health.  As  a  result  of  the  various  kinds  of 
observations  and  discussions  on  this  subject  of  late  years,  the 
localizationists  are  willing  to  admit  that  the  areas  of  the  cortex 
can  not  be  marked  off  msthematioally^that,  in  fact,  they 
"  overlap."    This  is  in  itself  an  important  concession.    Again, 


immattHnmmmm\mmi 


THE  BRAIN. 


(Mun 


625 


nnk)  had 
ex  concerned 
trtions  of  the 
>rtion  of  this 
farther,  that 
re  now  tinder 
I " ;  by  which 
ig  the  images 
I,  inability  to 
or  the  other 
visual  center 
laps  the  most 

t  only  denies 
in  producing 
ad  to  sensory 
z),  as  a  result 
•bes  removed, 
me  case,  the 
arts  (anterior 
removed  in  a 
e  joint  result 
wo,  concludes 
take  up  the 
3  localization 

more  consid- 
are  so  related 
the  body  that 
ovements  are 
replaces  the 
sociated  with 

nany  cases  it 
imor,  etc.)  by 
braiuHSurgery 
development, 
fully,  and  the 
rious  kinds  of 
ate  years,  the 
of  the  cortex 
in  fact,  they 
sion.    Again, 


there  is  less  confidence  in  the  location  of  the  various  sensory 
centers  than  of  the  motor  centers.  Most  investigators  are  be- 
lievers in  a  "  motor  area  "  par  excellence  (for  the  arm,  leg,  etc.) 
around  the  fissure  of  Rolando.  This  view  is  now,  so  far  as 
man  is  concerned,  widely  accepted. 

There  is  agreement  in  placing  the  sensory  centers  behind 
the  above-mentioned  motor  area,  and  especially  in  the  occipital 
lobes.  The  tendency  to  locate  a  visual  center  in  this  region  is 
growing  stronger.  There  is  much  disagreement  as  to  the  other 
sensory  centers  formerly  placed  in  the  angular  gyrus  and  tem- 
poro-sphenoidal  lobes.  The  intellectual  faculties  have  not  been^ 
located  in  any  such  sense  as  Gall  and  his  followers  attempted 
to  establish.  The  first  two  frontal  convolutions  are  those  per- 
haps to  which  localization  has  as  yet  been  least  applied.  Chiefly 
on  clinical  and  pathological  grounds  a  center  for  speech  has  long 
been  loca^«d  in  the  third  (left)  frontal  convolution  (Broca's)  and 
parts  immediately  behind  it.  It  has  been  observed  that,  when 
dise^^  attacks  this  area,'sp<)ech  is  interfered  with  in  some  way. 

(We  may  say  then,  generally,  that  the  tendency  at  the  present 
time,  both  on  the  part  of  physiologists  and  clinical  observers,  is 
to  admit  localization  to  some  degree  and  in  some  sense.  This 
has  been  the  result  in  part  of  experiments  on  the  dog  and  es- 
pecially on  the  monkey,  combined  with  the  discussion  of  clini- 
cal cases  >rhich  resulted  in  death  (followed  by  an  autopsy),  or 
of  others  marked  by  a  successful  diagnosis  and  removal  of 
lesions  or  other  treatment.  In  other  words,  the  truth,  if  it  will 
be  «x)ached  at  all,  must  be  reached  by  the  method  we  have  ad- 
vocated throughout  this  work— the  discussion  of  the  results  of 
as  many  different  methods  as  can  be  brought  to  bear  on  this  or 
any  other  subject.  Neither  the  experimental  nor  the  pathologi- 
cal method  can  settle  such  complex  questions,  as  we  shall  en- 
deavor to  show  when  we  return  to  the  subject  later. 

Tkt  Oinulakiffii  in  tlM  Bnin. — The  brain,  being  inclosed  within 
an  air-tight  bony  case,  its  circulation  is  of  necessity  peculiar. 
Since  any  undue  compression  of  the  eucephalon  may  lead  to 
oven  a  fatal  stupor,  it  is  clear  that  there  must  exist  some  pro- 
vision to  permit  of  the  excess  of  arterial  blood  that  is  required 
for  unusual  activity  of  the  brain.  It  is  to  be  borne  in  mind 
that  tbe  fluid  within  the  ventricles  is  continuous,  through  the 
foramen  of  Majendie  in  the  roof  of  thts  fourth  ventricio,  with 
that  surrounding  the  spinal  cord  (spinal  cavity) ;  ro  that  an 
increase  in  the  volume  of  the  encephalon  in  consequence  of  an 
aflSux  of  blood  might  be  in  some  degree  compensated  by  an 


J 


626 


ANIMAL  PHYSIOLOGY. 


(bMux  of  the  cerebro-spinal  fluid.  The  part  played  by  this  ar- 
rangement has,  however,  been  probably  overestimated.  But 
the  peculiar  venous  sinuses  do,  it  is  likely,  serve  to  regulate 
the  blood-supply ;  being  very  large,  they  may  answer  as  tem- 
porary overflow  receptacles.  An  inspection  of  the  fontanelles 
of  an  infant  reveals  a  beating  corresponding  with  the  pulse ; 
and,  when  a  large  part  of  the  cranium  is  removed  in  an  animal, 
a  plethysmograph  shows  a  rise  in  volume  corresponding  with 
the  pulse  and  the  respiratory  movements,  as  in  the  case  of  the 
fontanelles.  But,  besides  these,  periodic  waves  of  contraction 
are  now  known  to  pass  over  the  cerebral  arteries. 

Whether  the  latter  is  part  of  a  general  wave  traversing  the 
whole  arterial  system  is  as  yet  uncertain.  Though  there  is 
considerable  anastomosis  of  vessels  in  the  encephalon,  it  is  not 
equal  to  what  takes  place  in'  many  other  organs.  It  is  well 
known  that  a  clot  or  other  plug  within  a  cerebral  vessel  is 
more  serious  than  in  many  other  regions,  which  is  partly  to  be 
explained  by  the  lack  of  sufficient  anastomosis  for  the  vascular 
needs  of  the  parts.  It  is  also  well  known  that,  in  organs  which 
constitute  parts  of  a  related  series,  as  the  different  divisions  of 
the  alimentary  tract,  all  are  not  usually  at  the  same  time  vas- 
cular to  the  same  extent.  While  they  act  functionally  in  rela- 
tion to  each  other,  they  exemplify  also  a  certain  degree  of  inde- 
pendence. Such  a  condition  of  things  is  now  known  to  exist  in 
the  brain — i.  e.,  certain  areas  may  be  abundantly  supplied  with 
blood  as  compared  with  others ;  and  it  seems  highly  probable 
that  a  condition  of  equal  arterial  tension  throughout  is  scarcely 
a  normal  condition.  Though  the  quantity  of  blood  contained 
within  the  vessels  of  the  whole  brain  at  any  one  time  is  not  so 
large  as  in  some  other  organr  (glands),  yet  the  foregoing  facts 
and  the  rapidity  of  the  flow  must  be  take^^  into  account.  The 
capillaries  are  very  close  and  abundant,  in  the  gray  matter  es- 
pecially ;  and  it  is  to  be  borne  in  mind  that  it  is  chiefly  these 
vessels  which  are  concerned  in  the  actual  metabolism  (nutri- 
tion) of  parts.  However,  the  chemical  changes  in  the  nervous 
system  being  feeble,  it  would  appear  probable  that  it  does  its 
work  with  less  consumption  of  pabulum  than  other  parts  of 
the  body.  We  wish  to  lay  stress  on  the  local  nature  of  vas- 
cular dilatation  in  the  brain  as,  it  greatly  assists  in  explaining 
certain  phenomena  about  to  be  considered. 

Sto^lf.-^bservitions  upon  animals  from  which  portions  of 
the  cranium  had  been  removed,  so  that  the  brain  was  visible, 
show  that  during  sleep  the  blood-vessels  are  much  less  promi- 


mmm 


MMMM 


tmm 


THE  BRAIN. 


627 


id  by  this  ar- 
imated.  But 
9  to  regulate 
swer  as  tem- 
e  fontanelles 
>h  the  pulse; 
in  an  animal, 
ponding  with 
le  case  of  the 
f  contraction 

raversing  the 
)ugh  there  is 
ilon,  it  is  not 
s.  It  is  well 
)ral  vessel  is 
i  partly  to  be 
the  vascular 
organs  which 
t  divisions  of 
),m.e  time  vas- 
nally  in  rela- 
3gree  of  inde- 
irn  to  exist  in 
(upplied  with 
fhly  probable 
)ut  is  scarcely 
od  contained 
ime  is  not  so 
regoing  facts 
ccount.  The 
ay  matter  es- 
I  chiefly  these 
>olism  (nutri- 
1  the  nervous 
at  it  does  its 
ther  parts  of 
ature  of  vas- 
n  explaining 

li  portions  of 
ft  was  visible, 
ih  less  promi- 


nent than  usual ;  and  it  is  well  known  that  means  calculated  to 
diminish  the  circulation  in  the  brain,  as  cold  and  pressure,  favor 
sleep.  It  is  also  well  established  by  general  experience  that 
withdrawal  of  the  usual  afferent  impulses  through  the  various 
senses  favors  sleep.  A  remarkable  case  is  on  record  of  a  youth 
whose  avenues  for  sensory  impressions  were  limited  to  one  eye 
and  a  single  ear,  and  who  could  be  sent  to  sleep  by  closing 
these  against  the  outer  world.  Yet  this  subject  after  a  long 
sleep  would  awake  of  his  own  accord,  showing  that,  while  affer- 
ent impulses  have  undoubtedly  much  to  do  with  maintaining 
the  activity  of  the  cerebral  centers,  yet  their  automaticity  (in- 
depspdence)  must  also  be  recognized. 

(^It  is  a  matter  of  common  experience  that  weariness,  or  the 
exhaustion  following  on  pain,  mental  anxiety,  etc.,  is  favor- 
able to  sleep. 

A  good  deal  of  light  is  thrown  on  this  subject  by  hiberna- 
tion, particularly  in  mammals. 

From  special  study  of  the  subject  we  have  ourselves  learned 
that,  however  temperature  and  certain  other  conditions  may 
influence  this  state,  it  will  appear  at  definite  periods  in  de- 
fiance, to  a  large  extent,  of  the  conditions  prevailing.  Hiber- 
nrvtion,  we  are  convinced,  is  marked  by  a  general  slowing  of  all 
of  the  vital  processes  in  which  the  nervous  system  takes  a 
prominent  part.  (^Sleep  and  hibernation  are  closely  related.  In 
both  there  is  a  diminution  of  the  rate  of  the  vital  processes,  as 
shown  by  the  income  and  output,  measured  by  chemical  stand- 
ards, with  of  course  obvious  physical  signs,  as  slowed  respira- 
tion, circulation,  etc.  While  sleep,  then,  is  primarily  the  re- 
sult of  a  rhythmical  retardation  of  the  vital  processes,  especially 
within  the  nervous  system,  it  is  like  hibernation  in  some  de- 
gree (in  the  lowest  creatures,  without  a  nervous  system)  the 
outcome  of  that  rhythm  impressed  on  every  cell  of  the  organ* 
ism  and  the  influence  of  which  is  felt  in  a  thousand  ways,  that 
no^^ubt  we  are  quite  unable  to  recognize. 

/Dreaming  is  a  partial  activity  of  the  mind,  corresponding 
doubtless  to  functional  wakefulness  or  relatively  increased  ac- 
tion of  some  limited  part  or  parts  of  the  brain.  It  is  now  all  but 
certain  that  these  parts  are  more  vascular— i.  e.,  we  must  reckon 
with  a  localized  vascularity  and  functional  activity.  If  this  be 
recognised,  almost  all  the  peculiarities  of  the  dreaming  state 
may  be  understood.  Dreams  usually  lack  some  elements  that 
give  the  conapl(eit9ne88'  and  consistency  of  waking  thought— a 
matter  readily  understood,  as  well  as  the  unrest  of  a  dreamy 


J 


588 


ANIMAL  PHYSIOLOGY. 


night,  by  the  facts  above  considered.  It  is,  moreover,  highly 
probable  that  not  only  different  parts  of  the  brain  have  a  dif- 
ferent psychical  function,  but  iJso  that  in  any  one  chain  of 
thought  or  state  of  consciousness  only  a  certain  number  of  parts 
are  prominently  engaged ;  and  that  what  is  termed  confusion 
of  mind  is  probably  a  result  of  the  activity  of  certain  other 
centers  to  a  degree  unusual — ^L  e.,they  are  relatively  too  obtru- 
sive, hence  that  balance  essential  to  all  normal  activity,  psy- 
chical and  other,  is  lost. 

Specialization,  physiological  division  of  labor,  holds  here  as 
elsewhere. 

Hypnotim. — Ey  the  help  of  the  above  principles  the  subject 
of  hypnotism,  now  of  absorbing  interest,  may  be  in  great  part 
explained.  This  condition  is  characterized  by  loss  of  volition 
and  judgment.  It  may  be  induced  in  man  and  certain  other 
animals  by  prolonged  staring  at  a  bright  object,  assisted  by  a 
concentration  of  the  attention  on  that  alone,  as  far  as  possible, 
combined  with  a  condition  of  mental  passivity  in  other  respects. 
The  individual  gradually  becomes  drowsy,  and  finally  falls  into 
a  state  in  mar.y  respects  strongly  resembling  sleep.  With  each 
recurrence,  the  hypnotic  condition  is  usually  more  readily  in- 
duced, and  persons  have  passed  into  it  in  the  entire  absence  of 
the  usual  procedure,  having  simply  been  told  that  they  would 
be  thus  affected  at  a  given  hour.  There  is  no  special  influences 
emanating  from  peculiarly  gifted  mediums,  and  most  persons] 
may  be  hypnotised  to  a  greater  or  less  degree,  though  with ) 
unequal  readiness. 

The  manifestations  are  very  variable,  but  are  usually  char- 
acterized by  either  total  abolition  of  certain  sensory  percep- 
tions, by  their  enfeeblement,  or  by  one  or  both  of  these,  com- 
bined possibly  with  exaltation  of  others.  Thus,  aneesthesia 
may  be  so  great  that  surgical  operations  may  be  performed 
without  consciousness  of  pain.  The  muscular  sense  may  be 
good,  so  that  the  sub^oct  can  write  well.  He  may  smell  better 
than  usual,  so  as  to  be  able  to  detect  persons  by  the  odors  from 
a  portion  of  their  clothing,  like  a  dog.  There  may  coexist,  with 
vision  for  form,  color-blindness.  These  are  to  be  regarded  mere- 
ly as  examples,  from  numberless  curious  combinations.  Again, 
the  affection  of  sense  may  be  bilateral  or  only  unilateral. 

Hypnotism  proper  may  be  combine  .1  with  catalepsy,  a  con- 
dition in  which  the  limbs  remain  rigid  i~^  ^  hatever  condition 
they  may  be  placed.  Modifications  of  the  vascular  and  respira- 
tory systems  occur.    Other  animals  have  been  hypnotized,  as 


MlilMfaMltMMWii 


MNaWm< 


Bover,  highly 
1  have  a  dif- 
one  chain  of 
mber  of  parte 
ed  confusion 
certain  other 
sly  too  obtru- 
activity,  pay- 
holds  here  as 

es  the  subject 

in  great  part 

)ss  of  volition 

certain  other 

assisted  by  a 

ar  as  possible, 

other  respects. 

lally  falls  into 

p.    With  each 

)re  readily  in- 

bire  absence  of 

at  they  would 

ecial  influences 

most  persons^ 

though  with) 

)  usually  char- 
nsory  percep- 
of  these,  com- 
is,  aneesthesia 
be  performed 
sense  may  be 
ly  smell  better 
he  odors  from 
y  coexist,  with 
■egarded  mere- 
,tions.    Again, 
lilateral. 
Ualepsy,  a  con- 
ever  condition 
ar  and  respira- 
hypuotized,  as 


THE  BBAIN. 


629 


the  fowl,  rabbit,  Guinea-pig,  crayfish,  frog,  etc.  This  condition 
is  readily  induced  in  the  common  fowl,  more  especially  the 
wilder  individuals,  by  holding  the  creature  with  the  bill  down 
on  a  table  and  the  whole  animal  perfectly  quiet  for  a  short 
time.  Upon  the  removal  of  the  pressure  the  bird  remains  per- 
fectly passive  and  apparently  asleep  for  some  little  time. 

The  subject  of  hypnotism  and  allied  conditions  has  of  late 
received  close  attention  from  a  large  number  of  observers. 
Among  other  surprising  results  as  the  consequence  of  "  hypnotic 
suggestion,"  certain  pathological  effects  have  been  produced : 
thus,  placing  a  piece  of  tissue-paper  on  the  skin,  with  the  sug- 
gestion that  an  actual  blister  is  being  applied,  has  resulted  in 
the  usual  effects  of  such  treatment. 

(  Somnambvlism  is  very  similar  to  hypnotism.  Individuals 
have  been  known  to  walk,  ride,  climb,  go  upon  a  journey  and 
pay  toll,  and  also  to  perform  their  ordinary  avocations.  A 
student  has  been  known  to  write  a  sermon,  read  it  over,  and 
make  corrections,  and  when  a  piece  of  pasteboard  was  placed 
before  his  eyes  this  still  went  on,  showing  that  the  images 
were  mental. 

Without  being  actually  hypnotized,  by  careful  observation 
of  one's  experiences  for  a  considerable  period,  one  may  catch, 
as  it  were,  the  realization,  at  different  times,  of  the  various 
phenomena  that  characterize  the  hypnotic  condition,  even  to 
details — though  not,  of  course,  in  that  complex  combination 
which  would  result  in  such  partial  or  complete  loss  of  conscious- 
ness as  marks  the  actual  condition ;  for  in  that  case  observa- 
tion would  be  very  difficult,  if  not  impossible.  To  illustrate  our 
meaning  briefly,  one  may  walk  a  considerable  distance,  noticing 
absolutely  nothing  consciously,  but  wholly  absorbed  in  one 
idea,  or  possibly  without  any  distinct  train  of  thought.  In  such 
a  case  ther«^>  is  neither  vision,  hearing,  no^*  tactile  sensation  in 
the  ordinary  ^imm.  Tho  person  is,  in  fact,  for  the  tune  practi- 
cally in  the  soranambulistic  condition  or  one  closely  allied  to  it. 
There  are  times  wh<»n  vision  is  in  abeyance,  or  only  one  eye 
used.  Though  apparently  looking,  we  do  not  see.  The  sensory 
perceptions  from  the  skin  may  be  so  purely  unilateral  that  the 
other  side  is  practically  aneesthetic  from  close  attention  to  the 
condition  of  one  side.  All  are  familiar  with  unilateral  vaso- 
motor effects,  such  as  the  redness  and  "  burning  "  of  one  cheek 
or  one  ear,  and  so  of  many  other  expcriunces  that  might  be  re- 
ferred to  did  space  permit.  Such  realizations  furnish  the  highest 
kind  of  knowledge,  we  might  say  the  only  truo  knowledge. 


680 


ANIMAL  PHYSIOLOGY. 


ft 


Pathology  sheds  some  light  on  this  subject.  In  diseases  of 
the  membranes  of  the  brain,  all  the  sensory  phenomena  may 
be  so  heightened  as  to  become  painful.  Slight  sounds,  a  little 
light,  feeble  vibrations,  a  gentle  touch,  all  give  rise  to  effects 
out  of  proportion  to  the  usual  ones.  From  the  close  proximity 
of  these  membranes  to  the  cerebral  cortex,  we  may  assume  that 
they  are  affected.  This,  together  with  the  results  of  stimula- 
tion and  removal  of  the  surface  of  the  brain,  brings  us  some 
way  on  toward  an  explanation  of  sleep,  dreaming,  hibernation, 
hypnotism,  and  cerebral  localization  itself. 

One  physiologist  has  given,  as  an  explanation  of  hypnotism, 
etc.,  inhibition  of  the  cells  of  the  cerebral  cortex,  and  this,  with- 
in limits,  is  no  doubt  true.  The  facts  of  hypnotism  and  allied 
phenomena  seem  most  of  all  to  emphasize  the  dependence  of 
the  central  cells  when  acting  normally  on  afferent  impulses. 
But  we  have  already  dwelt  on  this  important  subject  suffi- 
ciently to  render  our  meaning  clear. 


Cbbebral  Localization  rsconsidbrbd. 

An  examination  of  the  phenomena  of  the  states  recently 
considered  can  leave  no  doubt  in  the  mind  that  certain  parts  of 
the  brain,  even  certain  portions  of  the  cerebrum,  may  be  active 
while  the  remaining  ones  are  in  abeyance  or  but  feebly  engaged ; 
and,  as  has  been  seen,  our  every-day  experience  is  an  illustration 
of  the  same  fact.  The  circulation  in  the  brain  points  clearly  to 
its  being  a  collection  of  organs,  with  a  certain  degree  of  inde- 
pendence. It  is  therefore  unreasonable  to  assume  that  all  parts 
of  the  cerebral  cortex  discharge  equally  the  same  functions. 
On  the  other  hand,  it  is  just  as  unwarrantable  to  assume  that, 
in  the  face  of  all  the  facts  of  physiology  as  now  known  to  us, 
there  are  very  precisely  limited  areas  with  as  exactly  restricted 
functions  discharged  independently  of  all  the  other  parts.  As 
we  have  frequently  insisted,  the  functions  of  an  organ  are  alone 
normal  when  in  proper  relation  to  all  the  parts  with  which  it 
is  connected — ^that  is,  in  fact,  with  the  entire  body.  We  learned 
that  any  conclusions  based  on  artificial  fistulee  of  the  digestive 
orf:iv>s  could  be  only  approximately  correct  at  best,  and  might 
be  very  far  from  the  truth  in  the  sense  to  which  we  now  refer. 
To  assume  tiuii  there  is  only  one  path  by  which  certain  classes 
of  impulses  mU'Sf  travel  in  the  spinal  cord  has  been  shown  to  be 
unwarranted.  Therefore,  to  argue  that  because  the  removal  of 
ft  certain  portion  of  the  brain  either  is  or  is  not  followed  by 


[n  diseases  of 
inomena  may 
mnds,  a  little 
rise  to  effects 
ose  proximity 
y  assume  that 
ts  of  stimula- 
rings  us  some 
I,  hibernation, 

of  hypnotism, 
md  thi8,with- 
sm  and  allied 
dependence  of 
rent  impulses, 
subject  suflfi- 


BED. 

itates  recently 
ertain  parts  of 
may  be  active 
iebly  engaged; 
an  illustration 
sints  clearly  to 
legree  of  inde- 
e  that  all  parts 
Ame  functions. 

0  assume  that, 
rr  known  to  us, 
EMJtly  restricted 
her  parts.  As 
3rgan  are  alone 
3  with  which  it 
y.  We  learned 
if  the  digestive 
test,  and  might 

1  we  now  refer, 
certain  classes 

»en  shown  to  be 

the  removal  of 

lot  followed  by 


THE  BRAIN. 


631 


no.  aM.— Lateral  mirfam  of  bnin  of  monkqr,  dlqtlajliif  motor 


(after  Honlqr  and 


Via.  MS. -Median  surfaoe  of  hnbt  of  moDkey  (after  Horatey  and  Schlfer). 
Figs.  384  and  ass  may  be  Mid  to  embody  Ike  vtews  of  Horaley  and  Sohkfer  oiore  eapeoiaar. 
m  ragaru  to  motor  looaluatioD, 

certain  aKxiitications  or-Unw  of  function,  proves  that  this  part 
is  or  is  tix>t  «>oncemed  with  that  particular  kind  of  activity,  does 
not  seem  to  be  logical 


{ 


J 


589 


ANIMAL  PUYSIOLOOr. 


Bi-J§* 


i 


I 

I 


1 


I 

I 


! 

i 

t 


luwiiMiM"  iiiiiuwiiwriifwiiiiiiMiiMWi  ip  imnw  m'  \ 


i 


I 


I 


'65 


^^•i; 


j' 


THE  BRAIN. 


083 


iM 


534 


ANIMAL  PHTSIOLOOT. 


If  it  be  true,  as  it  unquestionably  is,  that  a  certain  region 
of  the  cortex  or  other  portion  of  the  brain  is  normal  only  when 
in  relation  with  others,  it  follows  that  mere  removal  can  not 
entirely  solve  such  problems  as  the  function  of  the  different 
parts.  Nor  does  it  follow,  because  a  localization,  meeting  the 
needs  of  practical  medicine  and  surgery,  has  been  established, 
that  therefore  we  are  justified  in  assuming  that  a  scientific  lo- 
calization rests  upon  the  same  grounds.  Any  theory  that  fails 
to  recognize  both  the  interdependence  of  parts  and  the  resources 
of  nature  in  substituting  one  part  for  another  functionally, 
overlooks  principles  of  very  wide  application  in  biology.  We 
must  express  our  conviction  that  neither  ablation,  stimulation^ 
pathological  observation,  the  results  of  surgical  interference, 
nor  the  facts  of  clinical  medicine,  can  any  of  them  singly  settle 
such  questions. 

The  comparative  method  has  been  as  yet  but  little  used. 
Conclusions  in  regard  to  the  monkey  have  been  applied  not 
only  to  man  but  other  animals;  and  thatihe  Experiments  upon 
dogs  should  result  in  changes  or  the  absence  of  changes,  to 
which  there  is  uo  correspondence  in  the  monkey,  has  hardly 
been  recognized  as  it  should.  It  is  only  by  the  synthetical 
method,  as  we  have  so  often  urged,  that  even  an  approximation 
to  the  truth  or  a  part  of  it  can  be  attained.  Results  from  one 
method  or  another,  taken  alone,  may  be  positively  misleading, 
unless  interpreted  in  the  light  of  many  other  facts.  The  in- 
terpretation is  the  difficult  portion  of  the  task  in  the  study  of 
localization ;  but,  before  we  are  prepared  to  formulate  a  correct 
and  comprehensive  theory,  we  must  begin  lower  in  the  animal 
scale,  extend  observations  over  a  large  number  of  animals,  and 
complete  these  by  pathological  and  clinical  observations  on 
man  and  other  mammals.  If  the  spinal  cord  becomes  func- 
tionally what  it  is  in  any  case  largely  through  the  life  experi- 
ences of  the  individual,  this  must  also  apply  to  the  brain,  hencQ 
we  must  look  for  individual  as  well  as  gn^up  differences. 

The  loss  of  speech  (aphasia),  in  consequence  of  lesions  in  the 
left  third  frontal  convolution,  was  formerly  pointed  to  as  un- 
doubted evidence  of  localization ;  but,  the  more  this  subject  has 
been  studied,  the  more  clearly  it  has  been  perceived  that  even 
in  this  case  the  theories  of  a  rigid  localization  break  down. 

The  speech-center  has  had  its  boundaries  extended ;  and  it 
turns  out  that  a'vast  complex  of  connections  must  be  consid- 
ered, many  of  which  are  not  confined  to  the  third  frontal  con- 
volution or  its  neighborhood. 


mm^'.-'a**'i»iuf»i'aia»tmmHmmtm 


;ertain  region 
lal  only  when 
loval  can  not 

the  different 
,  meeting  the 
m  established, 
i  scientific  lo- 
9ory  that  fails 
1  the  resources 

functionally, 
biology.  We 
n,  stimulation^ 
I  interference, 
!n  singly  settle 

>ut  little  used, 
m  applied  not 
leriments  upon 
of  changes,  to 
ey,  has  hardly 
ihe  synthetical 
approximation 
jsults  from  one 
ely  misleading, 
facts.    The  in- 
n  the  study  of 
mlate  a  correct 
*  in  the  animal 
of  animals,  and 
jbservations  on 
becomes  func- 
the  life  experi- 
;he  brain,  hence 
ifferences. 
of  lesions  in  the 
ointed  to  as  tm- 
this  subject  has 
ieived  that  even 
)reak  down, 
xtended;  and  it 
must  be  consid- 
lird  frontal  con- 


THE  BRAIK. 


535 


/There  is  a  kind  of  experimental  evidence  that  throws  a  good 
deal  of  light  on  the  present  discussion.  It  is  found  that,  when 
certain  drugs  have  been  administered,  the  irritability  of  the 
cortex  is  either  increased  or  diminished,  according  to  the  stage 
of  action  of  the  drug  (morphia,  etc.).  It  is  not  impossible 
that  epileptiform  convulsions  may  result  from  the  application 
of  a  stimulus  of  almost  any  strength,  though  this  result  does 
not  follow  when  the  electrodes  are  applied  to  the  underlying 
white  substance.  The  disease  epilepsy  ha^  been  known  to  fol- 
low injuries  to  the  cranium  or  the  brain  membranes,  in  conse- 
quence of  which  the  cells  themselves  of  the  cortex  have  been 
altered  in  function.  Moreover,  the  epileptiform  movements 
may  be  in  such  cases  confined  to  certain  muscles,  thus  pointing 
to  a  motor  localization.  If  a  muscle  contraction,  as  the  result 
of  stimulation  of  a  rr  -  area  (the  animal  being  under  the  in- 
fluence of  morphia),  .  ecorded  by  the  graphic  method,  and  the 
sciatic  nerve  then  divided,  in  repeating  the  original  experiment, 
it  will  be  seen  that  the  whole  character  of  the  curve  is  altered, 
the  latent  period  having  been  lengthened,  and  the  height  of 
the  curve  lessened.  This  points  to  an  inhibitory  influence  exer- 
cised over  the  cortical  motor  cells,by  afferent  influences,  and  we 
are  at  once  reminded  of  Schiff's  theory ;  but  most  of  all  do  such 
experiments  enforce  that  close  relationship  of  all  parts  of  the 
body  which  finds  its  reflection  in  the  brain  cortex  as  elsewhere. 

We  have  dwelt  upon  the  subject  of  cerebral  localization  at 
length,  because  of  its  great  practical  and  scientific  importance, 
not  alone  for  medicine  and  physiology,  but  in  the  allied  depart- 
ment of  psychology.  In  conclusion,  we  may  express  the  view 
that  there  is  in  the  cerebral  cortex  a  localization  of  function, 
variable  for  each  group  of  animals,  and  to  some  extent  for 
each  individual ;  that  it  is  not  of  a  character  to  be  mapped  out 
by  mathematical  lines ;  that  in  case  of  disease  or  injury  one 
part  may  to  a  certain  extent  take  up  the  functions  of  another ; 
that  the  functions  of  any  part,  however  .limited,  are  only  to  be 
understood  when  taken  in  connection  with  all  other  parts  of 
the  cortex,  of  the  brain,  and,  in  fact,  of  the  entire  body.  These 
views  we  believe  to  be  borne  out  by  the  facts  of  physiological 
experiment,  clinical  medicine,  operative  surgery,  pathology, 
sleep,  dreaming,  hypnotism,  the  nature  of  the  cerebral  circu- 
lation, and  the  general  truths  of  biology. 

Oanlnal  Time. — We  have  already  considered  cerebral  reflex 
time,  and  now  proceed  to  examine  into  the  period  occupied  by 
a  mental  operation  involving  attention  and  volition. 


J 


fmm 


mmmm 


! 


'   •■ 


J 


686 


ANIMAL  PHYSIOLOGY. 


When  a  subject  makes  some  signal  in  response  to  a  stimu- 
lus, we  recognize  three  parts  to  the  entire  chain  of  events :  1. 
The  time  occupied  in  the  passage  of  the  afferent  impuliies  in- 
ward along  certain  lengths  of  nerve  from  a  peripheral  sense- 
organ.  2.  The  time  taken  up  by  the  processes  of  the  central 
cells  before  the  efferent  nervous  discharge  takes  place.  3.  The 
time  consumed  by  the  passage  of  the  efferent  impulses  from 
the  center  to  the  muscl?  involved.  The  whole  interval  is  termed 
the  reaction4ime,  whilo  the  second  constitutes  the  redticed  re- 
aviion-time. 

As  the  first  and  third  probably  vary  but  little,  it  is  highly 
probable  that  the  difference  in  the  reaction-time  obsex  vable  in 
different  individuals,  and  very  much  modified  by  thr>  condition 
at  the  moment  (as  fatigue),  and  especially  by  practice,  is  trace- 
able to  the  central  cells.  In  popular  language,  some  pennons 
are,  as  compared  with  others,  slow  thinkers.  Thiu  factor  iu  the 
"personal  equation,"  so  called.  There  are,  of  Coui-se,  many 
sources  of  error  in  .such  calculations,  but  approximate  results 
of  value  may  be  reached.  It  would  appear  that  the  reaction 
period  for  tactile  is  shorter  than  for  visual  or  audit  )ry  sensa- 
tions, while  that  of  vision  is  longer  than  for  hearing.  The 
respe^;tive  periods  have  been  set  down  as  about  ^  of  a  second 
for  viftion,  \  for  audition,  and  \  for  feeling. 

Ti.e  cputral  processes  may  be  reckoned  to  take  (for  percep- 
tlo  '    nd  <  ',V,tion)  about  -^ot  a,  second. 

li  dis*^ ;  iminations  have  to  be  made — so  as  to  decide,  e.  g., 
T  '\.  ther  it  is  the  right  or  the  left  side  of  the  body  that  has 
iioon  touched — a  longer  time  is,  of  course,  required,  and  the  re- 
action period  in  this  case  also  varies  greatly.  It  has  been  set 
dovn  as  occupying  from  gV  to  |  of  a  second.  Prom  these  con- 
siderations, it  will  be  plain  that "  the  lightning-like  rapidity 
of  thought "  is  a  rather  extravagant  figure  of  speech. 

Functions  of  other  Portions  op  the  Brain. 

Certain  parts  of  the  encephalon  are  spoken  of  as  the  basal 
ganglia,  prominent  among  which  are  the  corpus  striatum  and 
the  optic  thalamus. 

Th*  Oorpiii  Striatum  and  the  Optie  Thaluiu.— The  corpus 
striatum  consists  of  several  parts,  the  main  divisions  being  an 
intra-ventricular  portion  or  caudate  nucleus,  and  an  extra- 
ventriculnr  part  or  lenticular  nucleus. 

Between  these  lies  the  internal   capsule,  through  which 


■^ — -r-:ismltm 


Be  to  a  stimii- 
of  events:  1. 
impuliies  in- 
pheral  sense- 
>f  the  central 
)lace.  3.  The 
[npulses  from 
rval  is  termed 
le  redvcfid  re- 

le,  it  is  highly 
o1}seivable  in 
iho.  condition 
ctice,  is  trace- 
sonie  persons 
m  factor  is  the 
<:;oui*se,  many 
ximate  results 
t  the  reaction 
ndit  dry  sensa- 
hearing.  The 
I  ^  of  a  second 

ke  (for  percep- 

o  decide,  e.  g., 
body  that  has 
•ed,  and  the  re- 
It  has  been  set 
rom  these  con- 
?-like  rapidity 

Braik. 

of  as  the  basal 
s  striatum  and 

I.— The  corpus 
sions  being  an 
and  an  extra- 
through  which 


>iii.tiV    ^ 


-r-'ft" 


r 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


1.0 


I.I 


■50   "^^     M^H 

1^  1^    12.2 


u 

■yuu 


L25  114  11.6 


—    6" 


R' 


«^'3' 


°!» 


/ 


Photographic 

Sciences 

Corporation 


23  WEST  MAIN  STRUT 

WHSTCR.N.Y.  14580 

(716)  872-4503 


CIHM/ICMH 

Microfiche 

Series. 


CIHM/ICIVIH 
Collection  de 
microfiches. 


Canadian  Institute  for  Historical  Mlcroreproductlons  /  Instltut  Canadian  de  microreproductlons  historiques 


*Wli 


(f 


r 


t, , 


S3 


THE  BRAIN. 


687 


pass  fibers  that  spread  out  toward  the  cortex,  as  the  corona 
radiaia. 

i 


Fta  KB.— TnMvene  McUon  of  cerebral  hemispliereB,  at  level  of  cerebral  „ 
IMtoD).    1,  great  tongitudinal  llMure :  9,  part  of  Mune  between  occipital  lobea 


(afttr 
anterior 


part  <rf  corpus  caUoaum ;  4,  flmire  of  Sylvlua :  6.  convolutions  of  island  of  Beil  (insulat ;  0, 
cMidate  nocleuB  of  corpus  striatum  :  7,  lenticular  nucteua  of  o 


thalamus ;  0,  Internal  capsule ;  10,  external  capsule ; 


corpus  striatum  ;  8,  optic 
11,  daustrum. 


Pathology,  especially,  has  shown  that  a  lesion  of  the  intra- 
ventricular portion  of  the  corpus  striatum,  and,  above  all,  of 
the  internal  capsule,  is  followed  by  failure  of  voluntary  move- 
ment (akinesia).  It  would  appear  that  a  great  part  X)t  the 
'  fibers  from  the  motor  area  around  the  fissure  of  Rolando,  pass 
through  the  intra-ventricular  parts  of  the  corpus  striatum,  and 
especially  its  internal  capsule.  But  it  is  also  to  be  borne  in 
mind  that  a  large  part  of  the  fibers  passing  from  the  cortex 
make  connection  with  the  cells  of  the  corpus  striatum  before 
reaching  the  cord.  These  facts  render  the  occurrence  of  loss  of 
voluntary  motor  power  comprehensible. 

The  fibers  of  the  peduncles  of  the  brain  may  be  divided  into 


!i^>ii^3^;i?'t»lte',  7,'-^^  lA*  ;iJf'2!.i^ii:i^^ 


.■  .'NT''UI;?^^f*^^>--<t'S'" 


ANIMAL  PHYSIOLOGY. 


an  interior  or  lower  division  {crttsfa),  going  mostly  to  the  cor- 
pus striatum,  and  a  posterior  division  (t-egmentum),  passing 
principally  to  the  optic  thalmi ;  many,  possibly  most  of  them, 
ultimately  reach  the  cortex.  Many  clinical  observers  do  not 
hesitate  to  speak  of  the  optic  thalamus  as  sensory,  in  function 
and  the  corpus  striatum  as  motor ;  but  the  clinical  and  patho- 


i 
l 

1 


i: 


Fio.  WB.— TnuMfOTM  McUon  of  hnmaa  brafa  (aflar  DaMon).   Tlito  and  the  ptcoedinK  flgnm 
are aomewhat diagmmmaUc. . !{  poM VarplB ;  %», cmim  cerrtiri ;J, S, internal oapaule : 


4, 4,  corona  radlata ;  5,  optfc 


:6.i 


;r. 


logical  evidence  is  conflicting— all  lesions  of  these  parts  not 
being  followed  by  loss  of  sensation  and  motion  respectively ; 
though  an  injury  to  the  internal  capsule  generally  results  in 
paralysis.  All  are  agn'eed  that  the  symptoms  are  manifested 
on  the  side  of  the  body  opposite  to  the  side  of  the  lesion,  so 
that  a  decussation  must  take  place  somewhere  between  the 
ganglion  and  th^  periphery  of  the  body. 

There  is  no  doubt  that  the  optic  thalamus,  especially  its 
posterior  part,  is  concerned  with  vision,  for  injury  to  it  is  fol- 
lowed by  a  greater  or  less  degree  of  disturbance  of  this  func- 
tion. As  has  been  already  pointed  out,  unilateral  injury  of 
either  of  these  ganglia  leads  to  iuco-oi^ination  or  to  forced 
movements.  That  these  regions  act  some  intermediate  part  in 
the  transmission  of  impulses  to  and  from  the  brain  cortex,  and 
that  the  anterior  one  is  concerned  with  motor,  and  the  pos- 
terior possibly  with  sensory  (tactile,  etc.),  and  certainly  with 
visual  impulses,  may  be  state^  with  some  confidence,  though 
further  details  are  not  yet  a  subject  of  general  agreement. 


THB  BRAIN. 


689 


;o  the  cor- 
i),  passing 
t  of  them, 
jrs  do  not 
1  function 
uidpatho- 


preoediDK  flgnra 
nternal  oaprale : 
rUlomm. 

B  parts  not 
sspectively ; 
Y  results  in. 
manifested 
le  lesion,  so 
etween  the 

ipecially  its 
to  it  is  fol- 
'  this  fxmc- 
tl  injury  of 
tr  to  forced 
liate  part  in 
cortex,  and 
nd  the  pos- 
rtainly  with 
ince,  though 
lement. 


timpora  Qvadrigemina. — ^The  function  of  these  parts  in  vision, 
as  in  the  co-ordination  of  the  movements  of  the  ocular  muscles. 


or  flbwni 
nudtoi 


of  Imlii  on  tnoMvene  woUon  to  tUMlrate  ooun* 

3A«r  Ludota'y.    C,C,  oortox  oeiebrl;  0.$,  oorpiw  ■triatiun;  S.  i, Jentloutar 
T.  o,  optie  thalanMM:  J»,  jwdUMde ;  H,  tacmentuni ;  j»,  enaaU ;.  V, 


quadrimmlii*:  iTlloocowradtaUirffMi^Mtrte^    >, % o< lenficuUr nuolew ;  &Vo( 
oplto  aateaiH ;  ^  4,  of  oorpom  qiMdric«5na :  ^  diMot  ttwn  to  cor^ 
rf^  a,  «,«)«•  tram  oorpon  quiidriiiemlii*  to  tagmwitum  a  m.  f  urttwr  <w<»w  <«  <£«5 
«Sm ;  8, 8.  flbM«  tram  cStros  atrtatum  aad  tenticiilur  nuclein  to  crusUoT  iwdnnctoor 


WNbnim:  Jf.  fiurtbar oonrw of  tbaw :  AAooune  of  Miwofy libera ;  J7, truMrono  mo- 
tioa  of  iqi>liiiri  ooid ;«.  IT,  antorte,  awl  1^  IT,  iKNrtertor  raoto ;  a,  a,  aytrtem  of  MWM^ 
flben ;  c  c,  oommMMinl  flban. 

and  their  relations  to  the  movements  of  the  pupil,  will  he 
considered  later.  However,  the  actual  centers  for  these  func- 
tions seem  to  lie  in  the  anterior  portion  of  the  floor  of  the 
aqueduct  of  Sylvius,  and  are  indirectly  affected  by  stimulation 
of  the  corpora  quadrigemina.    Extirpation  of  these  parts  on 


ij#wfiffii«iiwi«riTiMi^^ 


MMimfliiiiWfaiWM^ 


r 


540 


ANIMAL  PHTSIOLOOT. 


K 


one.  side  produces  blindness  of  the  opposite  eye,  and  in  birds, 
etc.,  the  same  result  follows  when  their  homologues — the  optic 
lobes — are  similarly  treated.  There  can  be  no  doubt,  therefore, 
that  they  are  a  part  of  the  central  nervous  machinery  of  vision, 
and  it  seems  to  be  probable  that  the  anterior  parts  of  the  cor- 
pora quadrigemina  alone  have  this  visual  function.  But,  since 
it  is  the  opposite  eye  that  is  affected,  and  in  some  animals 
(rabbits)  that  alone,  we  are  led  to  infer  a  decussation  of  the 
optic  fibers,  or  at  least  of  impulses.  In  dogs,  on  the  other  hand, 
the  crossing  seems  to  be  but  partial.  From  the  fact  that  only 
a  part  of  the  visual  field  is  wanting  (hemianopsia — ^i.  e.,  that 
only  the  half  of  the  usual  field  of  view  is  visible),  and,  since 
there  may  be  hemianopsia  of  both  eyes,  with  unilateral  disease 
of  the  brain,  it  has  been  inferred  that  in  man  the  decussation 
is  also  incomplete.  We  may  remark  incidentally  that  it  has 
lately  been  maintained  that  removal  of  one  occipital  lobe  in  the 
monkey  leads  to  heminopsia  of  the  opposite  eye.  These  parts, 
as  we  have  already  seen,  take  some  share  in  the  co-ordination  of 
muscular  movements,  and  give  rise  to  forced  movements  after 
unilateral  injury. 

It  begins  to  appear  that  there  are  several  parts  of  the  brain 
concerned  with  vision.  After  removal  of  almost  any  part  of 
the  cerebral  cortex,  if  of  sufficient  extent,  vision  is  impaired. 
We  may  say,  then,  that,  before  an  object  is  "  seen  "  in  the  high- 
est sense,  processes  beginning  in  the  retina  undergo  further 
elaboration  in  the  corpora  quadrigemina,  optic  thalami,  and, 
finally,  in  the  cerebral  cortex.  We  may  safely  assume  that  the 
part  played  by  the  latter  is  of  very  great  importance,  making 
the  perception  assume  that  highest  completeness  which  is  of 
very  varying  character,  no  doubt,  with  different  groups  of 
animals.  In  a  sense,  all  mammals  may  see  alike,  and,  in  an- 
other sense,  they  may  see  things  very  differently ;  for,  if  we 
may  judge  by  the  diffeiwnces  in  this  respect  between  educated 
and  uneducated  men,  the  great  dissimilarity  lied  in  the  inter- 
pretation of  what  is  seen ;  in  a  word,  the  cortex  has  to  do  with 
the  perfecting  of  visual  impulses.  Nevertheless,  a  break  any- 
where in  the  long  and  complicated  chain  of  processes  must  lead 
to  some  serious  impairment  of  vision.  Much  of  the  same  sort 
of  reasoning  applies  to  the  other  senses  and  also  to  speech. 
/~XTo  speak,  therefore,  of  a  visual  center  or  a  speech  center  in 
any  very  restricted  sense  is  unjustifiable ;  at  the  same  time,  it 
is  becoming  clearer  that  there  is  in  the  occipital  lobe,  rather 
than  in  other  parts  of  the  cortex,  an  area  which  takes  a  pecul- 


THE  BRAIN. 


641 


id  in  birds, 
1 — ^the  optio 
b,  therefore, 
ry  of  vision, 
of  the  cor- 

But,  since 
me  animals 
ktion  of  the 
other  hand, 
3t  that  only- 
lb — ^i.  e.,  that 
),  and,  since 
teral  disease 
decussation 

that  it  has 
kl  lobe  in  the 
These  parts, 
>rdination  of 
sments  after 

of  the  brain 
any  part  of 
is  impaired, 
in  the  high- 
ergo  further 
halami,  and, 
ume  that  the 
iince,  making 
i  which  is  of 
it  groups  of 
e,  and,  in  an- 
y ;  for,  if  we 
reen  educated 
in  the  inter- 
as  to  do  with 
a  break  ony- 
ises  must  lead 
the  same  sort 
o  speech. 
)ech  center  in 
same  time,  it 
d  lobe,  rather 
takes  a  pecul- 


iar and  special  share  in  elaborating  visual  impulses  into  visual 
sensations  and  perceptions;  and  there  can  be  little  doubt 
that  the  other  senses  are  represented  similarly  in  the  cerebral 

cortex. 

The  C0r«Mlii]ii.-<(Both  physiological  and  pathological  re- 
search point  to  the  conclusion  that  the  cerebellum  has  an  im- 
portant share  in  the  co-ordination  of 'muscular  movements. 
Ablation  of  parts  of  the  organ  leads  to  disordered  movements; 
and,  when  the  whole  is  removed  in  the  bird,  co-ordination  is 
all  but  impossible,  and  the  same  holds  for  mammals.  Section 
of  the  middle  peduncle  of  one  side  is  liable  to  give  rise  to  roll- 
ing forced  movements.  In  fact,  injury  to  the  cerebellum  causes 
symptoms  very  similar  to  those  following  section  of  the  semi- 
circular canals,  so  that  many  have  thought  that  in  the  latter 
case  the  cerebellum  had  itself  been  injured. 

PathfllogiaaL — Tumors  and  other  lesions  frequently,  though 
not  invariably,  give  rise  to  unsteadiness  of  gait,  much  like  that 
affecting  an  intoxicated  person.  It  may  safely  be  said  that  the 
cerebellum  takes  a  very  prominent  share  in  the  work  of  the 
muscular  co-ordination  of  the  body. 

As  has  already  been  pointed  out,  several  tracts  of  the  spinal 
cord  make  connection  with  the  cerebellum,  and  it  is  not  to  be 
forgotten  that  this  part  of  the  brain  has,  in  general,  most  ex- 
tensive connections  with  other  regions.    Insufficient  study  has 
as  yet  been  given  to  the  cerebellum,  and  it  is  likely  that  the 
part  it  takes  in  the  functions  of  the  eucephalon  is  greater  than 
has  yet  been  rendered  clear.  -ZChe  old  notion  that  thw^q^^ 
bears  any  direct  relation  to  the  sexual  fnnctioM  seems  to3§^ 
#iiK6nnonndatiomr"in&a8  now  been  clearly  demonstrated: 
fl^t  the  lower  re^on  of  the  spinal  cord  is,  in  the  dog  and  prob- 
ably most  mammals,  the  part  of  the  nerve-centers  essential  forj 
the  sexual  processes. 

Onuft  Otnbri  and  Pons  VanliL— As  has  been  already  noted, 
the  peduncles  (crura)  are  the  paths  of  impulses  from  certain 
parts  of  the  cerebral  cortex,  the  basal  ganglia,  and  the  spinal 
cord.  The  functions  of  the  gray  matter  of  the  crura  are  un- 
known. But,  since  forced  movements  ensue  on  unilateral  sec- 
tion, it  is  plain  that  they  also  have  ta  do  with  muscular  co- 
ordination. 

The  transverse  fibers  of  the  pons  Varolii  connect  the  two 
halves  of  the  cerebellum.  Its  longitudinal  fibers  have  extensive 
connectitms— the  anterior  pyramids  and  olivary  bodies  of  the 
medulla,  the  lateral,  and  perhaps  also  a  part  of  the  posterior 


MHMKMMWIMHItHfeHMHiiKHWtilM 


'>raW£H 


MIMWi>ili<iMlMlliawa<*MV.aat-;i^ 


542 


ANIMAL  PHYSIOLOGY. 


.'.iS* 


columns  of  the  cord,  while  upward  these  fibers  connect  with 
the  crura  cerebri  and  so  with  the  cortex. 

PathiolofiML— Paralysis  of  the  face  usually  occurs  on  the 
same  side  as  that  of  the  rest  of  the  body ;  hence  it  must  be 
inferred  that  there  is  a  decussation  somewhere  of  the  fibers  of 
the  facial  nerve ;  but  there  is  much  still  to  be  learned  about  this 
subject. 

Madnlla  OUongata.— In  some  animals  (frogs)  it  is  certainly 
known  that  this  region  of  the  brain  has  a  co-ordinating  func- 
tion, and  it  is  probable  that  it  is  concerned  with  such  uses  in 
all  animals  that  possess  the  organ,  or  rather  collection  of  organs, 
seeing  that  this  part  of  the  brain  must  be  regarded  as  especially 
a  mass  of  centers,  the  functions  of  which  have  been  already 
considered  at  length.  So  long  as  the  medulla  is  intact,  life  may 
continue;  but,  except  under  special  circumstances,  which  do 
not  invalidate  this  general  statement,  its  destruction  is  followed 
by  the  death  of  the  animal. 

We  may  simply  enumerate  the  centers  that  are  usually  | 
located  in  the  medulla:  The  respiratory  (and  convulsive),  car- 
dio-inhibitory,  vaso-motor,  center  for  deglutition,  center  for 
the  movements  of  the  gullet,  stomach,  etc.,  and  the  vomiting 
center ;  center  for  the  secretion  of  saliva  and  possibly  other  of  ^ 
the  digestive  fluids.    Some  add  a  diabetic  and  other  centers. 


Special  Considbbations. 

liiilirsridiigieal. — The  further  we  progress  in  the  study  of  the 
nervous  system,  the  greater  the  significance  of  the  facts  of  its 
early  development  becomes.  It  will  be  remembered  that  from 
that  uppermost  epiblastic  layer  of  cells  so  early  nuirked  off  in 
the  blastoderm,  is  formed  the  entire  nervoxis  system,  including 
centers,  nerves,  and  end  organa    The  brain  may  be  regarded 


B^Ck  an.— Vertieal  longitttdlnalMctloD  of  brain  of  hninmemtiqrooC  fourth  Int. 

(After  ShMiiey  and  Reicbert.)  e,  cerebral  bemlqidiera :  oe,  corpus  calkMuin  begimiiiiK  to 
paw  back ;  /,  foramen  of  Munro ;  o,  membrane  over  tbird  Tentrlcle  and  tbe  pineal  body ; 
Ih,  thalamus ;  S,  third  Tentrlcle ;  /,  olfaottirjr  bulb ;  eg,  corpora  quadrlgemlna ;  er,  omm 
cerebri,  and  abore  tbem,  aqueduct  of  SylVtas,  atUI  wmIb  ;  &,  cerebellum,  and  below  it  tte 
fourth  ventricle;  pv,  pons  VaroUi ;  m,  medulla  Oblongata. 


%^-. 


THE  BRAIN. 


648 


}nnect  with 

;urs  on  the 

it  must  be 

he  fibers  of 

i  about  this 

is  certaixily 
ukting  f  unc- 
auch  uses  in 
>n  of  organs, 
18  especially 
een  already 
kct,  life  may 
I,  which  do 
L  is  followed 

are  usually] 
ulsive),  car- 
,  center  for 
le  vomiting 
bly  other  of , 
r  centera 


itndy  of  the 
)  facts  of  its 
d  that  from 
orked  off  in 
n,  including 
be  regarded 


as  a  specially  differentiated  part  of  the  anterior  region  of  the 
medullary  groove  and  its  subdivisions ;  and  the  close  relation 
of  the  eye,  ear,  etc.,  to  the  brain  in  their  early  origin,  is  not 
without  special  meaning,  while  the  more  diffused  sensory  de- 
velopments in  the  skin  connect  the  higher  animals  closely  with 
the  lower — even  the  lowest,  in  which  sensation  is  almost  wholly 
referable  to  the  surface  of  the  body. 


MBtraeki.  1  ■>. 
Miim  beeinninR  to 
ItheplMalb^; 
gmiliuk;  cr,  onm 
1,  MKl  balow  it  the 


Fw.  IBS. 

Ito.  a8B.M)utMr  aurlMe  of  hamaa  fostel  brain  at  riz  montha,  diowiiMr  otIrIii  ct  prinoipsl 
flMorcs  (after  Siiarpqr  and  B.  Wagner).  F,  frontal  lobe ;  P,  parietal ;  O.  occ^al ;  T, 
tenponl ;  tt,a,a,  fktnt  aiipearanoe  of  wretnl  frontal  oonTolutfons ;  «, «,  sylvian  flMore ; 
»',  anterior  diTUrioa  ot  eame ;  C.  central  lobe  of  iiland  of  Bell ;  r,  flmire  of  Rolando ;  p, 
«ztemal  perpendlealarflMare. 

Ho.  818.— Upper  mrlkee  ot  brain  repreaented  in  Fig.  OqO  (after  Sharpey  and  R.  Wagner). 

Without  some  knowledge  of  the  mode  of  development  of 
the  encephalon,  it  is  scarcely  possible  to  appreciate  that  rising 
grade  of  complexity  met  with  as  we  pass  from  lower  to  higher 
groups  of  animals,  especially  noticeable  in  vertebrates ;  nor  is 
it  possible  to  recognize  fully  the  evidence  fovmd  in  the  nervous 
system  for  the  doctrine  that  higher  are  derived  from  lower 
forms  by  a  process  of  evolution. 

XvdvUoB. — ^The  same  law  ap'  mIps  to  the  nervous  system  as 
to  other  parts  of  the  organism,  vi: .,  that  the  individual  devel> 
opment  (ontogeny)  is  a  synoptical  representation,  in  a  general 
way,  of  the  development  of  the  group  (phylogeny).  A  com- 
parison of  the  development  of  even  man%  brain  reveals  the  fact 
that,  in  its  earliest  stage,  it  is  scarcely,  if  at  all,  distinguishable 
from  that  of  any  of  the  lower  vertebrates.  There  is  a  period 
when  even  this,  the  most  convoluted  of  all  brains,  is  as  smooth 
and  devoid  of  gyri  as  the  brain  of  a  frog.  The  extreme  com- 
plexity of  the  human  brain  is  referable  to  excessive  growth  of 


iiwiW«itei<iWlri«ifi 


544 


ANIMAL  PHY8I0L0OY. 


certain  parts,  crowding  and  alteration  of  shape,  owing  to  the 
influence  of  its  bony  case,  its  membranes,  etc. 


Fio.  904.— A,  brain  of  aye-ayeJLciMiir):  B,  of  mamioMt ;  O,  of  nuiiTel-inoDker  ICattiihrix); 
D.  of  mmcaque  mookey ;  E,  of  gibbon ;  F,  of  •  flfth-month  bunwn  foatus  (after  Owen). 
AltbooKb  naturaliita  are  agreed  tbat  the  monkeyt,  apea,  and  lemur*  are  related,  coniider- 
ablediitei«noesaretobeolMerf«dintbeirbrainB.  Tbeaaflgurea  alio  tthMtratellie  remark 
made  after  tbe  foUowtng  ones. 

Cit  is  evident,  from  an  inspection  of  the  cranial  cavities  of 
those  enormous  fossil  forms  that  preceded  the  higher  verte- 
brates, that  their  brains,  in  proportion  to  their  bodies,  were 
very  small,  so  that  any  variation  in  the  direction  of  increase 
in  the  encephalon— especially  the  cerebrum — must  have  given 
the  creatures,  the  subject  of  such  variation,  a  decided  advan- 
tage in  the  struggle  for  existence,  and  one  which  may  partly 
account,  perhaps,  for  the  extinction  of  those  animals  of  vast 
proportions  but  limited  intelligence.   That  the  size  of  the  brain 


Fia.  886.— A,  brain  of  a  cbekmiaa ;  B,  of  a  fcetal  oalt ;  C,  of  a  oat.  (All  after  Oesenbaar.) 
/  indicates  cerebral  hemiapheres;  II,  thalamus;  III,  corpora  quadrigenina;  IV,  cerebel- 
lum; V,  meduUa;  ««,  corpus  striatum ;  jT,  fornix ;  A,  bippocammis ;  «r,  fourlli rentrtcle ; 
o,  geniculate  body ;  ol,  dtactory  lobe,  it  will  be  obaenred  (1)  now  the  foetal  brain  in  a 
UKher  animal  form  resembles  the  developed  brain  in  a  lower  form,  and  (9)  how  certain 
parts  become  crowded  together  and  covered  over  by  more  prominent  regions,  e.g.,  the 
cerebrum,  as  we  ascend  the  animal  scale. 


THE  BRAIN. 


645 


(ring  to  the 


nkej  (CamiKHx); 
rtus  (kft«r  Owen). 
I  related,  coiuider- 
MtnOelliereiiMrk 


I  cavities  of 
igher  verte- 
bodies,  were 
I  of  increase 
,  have  given 
lided  advan- 
may  partly 
nals  of  vast 
of  the  brain 


after  OeoenlNuir.) 
nina;  /F,cerobel- 
r,  tourai  Tenttlele ; 
»  total  brain  in  a 
•nd  (9)  how  certain 
tregliws,  •.!(.,  the 


as  well  as  its  quality  can  be  increased  by  use,  seems  to  have 
been  established  by  the  measurements,  at  different  periods  of 
development,  of  the  heads  of  those  engaged  in  intellectual  pur- 
suits, and  comparing  the  results  with  those  obtained  by  similar 
measurement  of  the  heads  of  those  not  thus  specially  employed. 
Of  course,  it  must  be  assumed  that  the  head  measurement  is  a 
gauge  of  the  size  of  the  brain,  which  is  approximately  true,  if 


Fia. 


Fio.  9tt. 


Fio.  aM.-Brain  at  eat.  Men  t.-om  above  (after  Tiedanann). 
Fia.  8V7.— Brain  of  dog,  Men  f-om  above  (after  Tiedemann). 

not  entirely  so.    There  F.n,  many  facts  which  go  to  show  that 
thsi  hftbits  of  %n££^to^jer.djto  become  almost  the  instincts  of 
posterity^ven  in  the  c<»^  e  of  man.    It  has  heen  noticed  that  a^ 
facililymthe  acfjjuisition  of  scholarship  (languages,  literature)^ 
has,  in  many  cases,  been  associated  with  scholarly  habits  in) 
numerous  generations  of  ancestors.    The  inheritance  of  mental\ 
traits,  which  can  not  be  considered  wholly  apart  from  a  physi-j 
cal  basis  in  the  nervous  system,  and  especially  in  the  cefebrum,( 
is  a  subject  of  great  interest,  but  tc»o  wide  for  more  than  a  pass-) 
ing  allusion  here. 

utecent  investigations  seem  to  show  that  the  development 
of  the  ganglion  cells  of  the  brain  takes  place  first  in  the  me- 
dulla, next  in  the  cerebellum,  after  that  in  the  mid-brain,  and 
finally  in  the  cerebral  cortex.  Animals  most  helpless  at  birth 
are  those  with  the  least  development  of  such  cells.  The  me- 
dulla may  be  regarded  in  some  sense  as  the  oldest  (phylogeneti- 
cally)  part  of  the  brain.  In  it  are  lodged  those  cells"  (centers) 
which  are  required  for  the  maintenance  of  the  functions  essen- 
tial to  somatic  life.  This  may  serve  to  explain  how  it  is  that 
so  many  centers  are  there  crowded  together.  It  is  remarkable 
that  so  small  a  part  of  the  brain  should  preside  over  many  im- 
portant functions ;  but  the  principle  of  concentration  with  pro- 
gressive development,  and  the  law  of  habit  mi^ng  automatism 

8S 


iiw  Mir  fitniif 


646 


ANIMAL  PHTSIOLOOT. 


prominent,  throw  some  light  upon  these  facts,  and  especially 
the  one  otherwise  not  easy  to  understand,  that  so  much  impor- 
tant work  should  be  done  by  relatively  so  few  cells.  Possibly, 
however,  if  localization  is  established  as  fully  as  it  may  eventu- 
ally be,  this  also  will  not  be  so  astonishing. 

Nevertheless,  the  doctrine  that  so  small  a  region  of  the 
medulla  as  is  the  vaso-motor  center,  for  example,  should  con- 
trol so  many  different  vascular  tracts,  ought  not  to  be  finally 
accepted  without  close  examination.  •  It  is  so  easy  to  speak  of  a 
"  center  "  for  any  function  and  to  locate  it  in  the  medulla ;  but 
it  is  not  unlikely  that  the  physiology  of  the  future  will  greatly 
modify  our  present  teaching  in  this  regard.  As  in  many  other 
cases,  the  explanations  seem  to  be  too  simple  and  too  artificial. 
(T7ie  law  of  habit  has,  in  connection  with  our  psychic  life 
and  that  of  other  mammals,  some  of  its  most  striking  develop- 
ments. This  has  long  been  recognized,  though  that  the  same 
law  is  of  universal  application  to  the  functions  of  the  body  has 
as  yet  received  but  the  scantiest  acknowledgment. 

We  shall  not  dwell  upon  the  subject  beyond  stating  that  in 
our  opinion  the  psychic  life  of  animals  can  be  but  indifferently 
understood  unless  this  great  factor  is  taken  into  the  account ; 
and  when  it  is,  much  that  is  apparently  quite  inexplicable  be- 
comes plain.  That  anything  that  has  happened  once  any- 
where in  the  vital  economy  is  liable  to  repetition  under  a 
slighter  stimulus,  is  a  law  of  the  utmost  importance  in  physiol- 
ogy, psychology,  and  pathology.  The  practical  importance  of 
this,  especially  to  the  young  animal,  is  of  the  highest  kind. 

The  doctrine  of  a  "  cortical  projection "  for  the  senses,  or 
cortical  sense-centers,  has  enough  foundation  to  enable  us  to 
draw  certain  inferences  relative  to  the  direction  to  be  given  to 
(;the  education  of  youth.  If  true,  then  the  education  of  the' 
defiies  ^as  a  fhoroughly  good  foundation  in  physiology,  and 
"manual  training"  should  receive  the  hearty  support  of  sci-i 
entists.  It  follows  that  in  developing  the  senses  we  are  develV 
oping  the  most  important  part  of  the  brain  for  all  higher  endsj) 
the  cerebral  cortex. 

It  will  now  also  be  clear  that  if  there  are  cortical  motor  re- 
gions, then  the  size  of  the  cerebrum  and  the  muscular  develop- 
ment may  stand  in  a  closer  relation  than  we  have  been  wont  to 
believe.  That  connection  of  the  muscular  sense,  tactile  sensi- 
bility, sight,  etc.,  aimed  at  in  "  manual  training,"  is  in  harmony 
with  what  we  have  frequently  urged  in  relation  to  the  mutual 
dependence  of  one  part  of  the  brain  upon  another.    Both  theo- 


THE  BRAIN. 


547 


nd  especially 
much  Impor- 
Is.    Possibly, 

I  may  eventu- 

Bgion  of  the 
),  should  con- 
to  be  finally 
to  speak  of  a 
medulla;  but 
8  will  greatly 
n  many  other 
too  artificial. 
r  psychic  life 
ting  develop- 
that  the  same 
'  the  body  has 

• 

bating  that  in 
b  indifferently 
)  the  account ; 
explicable  be- 
ed  once  any- 
ition  under  a 
ice  in  physiol- 
importance  of 
hest  kind, 
the  senses,  or 
>  enable  us  to 
to  be  given  to 
ication  of  the"^/ 
aysiology,  and^ 
mpport  of  Bci-) 
i  we  are  deveW 

II  higher  ends^ 

tical  motor  re- 
icular  develop- 
e  been  wont  to 
),  tactile  sensi- 
is  in  harmony 
.  to  the  mutual 
)r.    Both  theo- 


retically and  practically  it  is  important  to  recognize  that  the 
value  of  vision,  indeed,  the  extent  to  which  we  "  see,"  is  in  no 
small  degree  related  to  what  we  feel.  The  carpenter  judges  dis- 
tances well  by  his  eye,  because  he  is  constantly  correcting  his 
visual  judgments  by  his  tactile  sense,  his  muscular  sense,  etc. 

We  must  point  out,  however,  that  the  special  developments 
of  disease  at  the  present  day  point  to  the  dangers  of  an  undue 
use  or  development  of  the  cerebrum.  That  balance  indispen4 
sable  for  health  must  be  preserved,  if  the  race  is  to  avoid  degen-i 
eration. 

SyaoptioaL-^Thcre  is  as  yet  no  systematized  clear  physiology 
of  "  the  brain."  We  are  conversant  with  certain  phenomena 
referable  to  this  organ  in  a  number  of  animals,  chiefly  the 
higher  mammals ;  but  our  knowledge  is  as  yet  insufficient  to 
generalize,  except  in  the  broadest  way,  regarding  the  functions 
of  the  brain — i.  e.,  to  determine  what  is  common  to  the  brains  of 
all  vertebrates  and  what  is  peculiar  to  each  group.  Referring, 
then,  to  the  higher  mammals,  especially  to  the  dog,  the  cat,  the 
monkey,  and  man,  we  may  make  the  following  statements : 

The  medulla  oblongata  is  functionally  the  ruler  of  vegeta- 
tive life — the  lower  functions ;  and  so  may  be  regarded  as  the 
seat  of  a  great  number  of  "centers,"  or  collections  of  cells  with 
functions  to  a  large  degree  distinct,  but  like  close  neighbors, 
with  a  mutual  dependence. 

Phylogenetically  (ancestrally)  the  medulla  is  a  very  ancient 
region,  hence  the  explanation  apparently  of  so  many  of  its 
functions  being  common  to  the  whole  vertebrate  group. 

Parts  of  the  mesencephalon,  the  pons  Varolii,  the  optic  lobes 
or  corpora  quadrigemina,  the  crura  cerebri,  etc.,  are  not  only 
connecting  paths  between  the  cord  and  cerebrum,  but  seem  to 
preside  over  the  co-ordination  of  muscular  movements,  and  to 
take  some  share  in  the  elaboration  of  visual  and  perhaps  other 
sensory  impulse& 

The  cerebellum  may  have  many  functions  unknown  to  us. 
Its  connections  with  other  parts  of  the  nerve-centers  are  numer- 
ous, though  their  significance  is  in  great  part  unknown.  Both 
pathological  and  physiological  investigation  point  to  its  hay- 
ing a  large  share  in  muscular  co-ordination. 

Iljscertain  that  the  cerebrum  is  the  part  of  the  brain  essen- 
tial foira3r~{E(Oijpier  psychic  manifestations  in  the  most  ad^ 
vanc(^  mammals  and  in  man.  '-' 

(The  preponderating  development  of  man's  cerebrum  ex- 
plains at  once  his  domination  in  the  animal  world,  his  power 


> 

I 


548 


ANIMAL  PHYSIOLOGY. 


over  the  inanimate  forces  of  Nature  and  his  peculiar  infirmitiesi 
tendencies  to  a  certain  class  of  diseases,  etc.— in  a  word,  man  is 
man,  largely  by  virtue  of  the  size  and  peculiarities  of  this  part 
of  his  brain. 

Modern  research  has  made  it  clear  also  that  there  is  a  "  pro- 
jection" of  sensory  and  motor  phenomena  in  the  cerebral  cor- 
tex ;  in  other  words,  that  there  are  sensory  and  motor  centers 
in  the  sense  that  in  the  cortex  there  are  certain  cells  which  have 
an  important  share  in  the  initiation  of  motor  impulses,  and  oth- 
ers employed  in  the  final  elaboration  of  sensory  ones. 

It  is  even  yet  premature  to  dogmati-^ie  in  regard  to  the  site 
of  these  centers ;  especially  are  we  not  i.-eady  for  large  generali- 
zations. In  man  the  convolutions  around  the  fissure  of  Rolando 
constitute  the  motor  area  best  determined. 

The  whole  subject  of  cortical  localization  requires  much  ad- 
ditional study,  especially  by  the  comparative  method  in  the 
widest  sense— i.  e.,  by  a  oomparisou  of  the  results  of  operative 
procedure  in  a  variety  of  groups  of  auimals,  and  the  results  of 
clinical,  pathological,  physiological,  and  psychological  investi- 
gation. Especially  must  allowance  be  made  for  differences  to 
be  observed,  both  for  the  group  and  the  individual;  and  also 
for  the  influence  which  one  region  exerts  over  another.  Be- 
tween the  weight  of  the  cerebrum,  the  extent  of  its  cortical 
surface,  and  psychic  power,  there  is  a  general  relationship. 


GENERAL  REMARKS  ON  THE  SENSES. 

Our  studies  in  embryology  have  taught  us  that  all  the  vari- 
ous forms  of  end-organs  are  developed  from  the  epiblast,  and 


Fio.M8.-P»pOUBof  bMii  of  palm  of  hMid  (after  Sm»p?y).    A  woular  network  In  all 
•"■  ^^Uid  in  some  nen^  and  UMStUeoorpuMdaa,  enter  Uiepapllln. 


^r  infirmities^ 
word,  man  is 
}  of  this  part 


ere  is  a  "  pro- 
cerebral  cor- 
notor  centers 
s  which  have 
ilses,  and  oth- 


^rd  to  the  site 
\Tge  generali- 
re  of  Rolando 

ires  much  ad- 
lethod  in  the 
}  of  operative 
the  results  of 
igical  investi- 
differences  to 
.ual ;  and  also 
another.  Be- 
>f  its  cortical 
itionship. 


GENERAL  REMARKS  ON  THE  SENSES. 


649 


so  may  be  regarded  as  modified  epithelial  cells,  with  which  are 
associated  a  vascular  and  nervous  supply.  These  end-organd 
are  at  once  protective  to  the  deli- 
cate nerves  which  terminate  in 
them,  and  serve  to  convey  to  the 
latt^er  peculiar  impressions  which 
are  widely  different  in  most  in- 
stances from  those  resulting  from 
the  direct  contact  of  the  nerve  with 
the  foreign  body.  All  are  ac- 
quainted with  the  fact  that,  when 


Fm.aM. 


FlO.40a 


IJo.  m.-Ooraoaole  of  Vater  (After  Bnw). 

Flo.  «W.-Xiid-bunM  (oorpuMlM)  of  Kiwue  (after  Ludden).    A,  from  conjunctiva  of  man : 

B,  from  conlunctiTact  calf.    It  mar  be  notloed  that  in  aU  Ume  caWtbe  nerve  kMsa  Us 

non  nwentlil  part*  Iwf ore  entering  Uie  oorpuade. 

the  epithelium  is  removed,  as  by  a  blister,  we  no  longer  possess 
tactile  sensibility  of  the  usual  kind,  and  experience  pain  on 
contact  with  objects ;  in  a  word,  the  series  of  connections  neces- 
sary to  a  sense-perception  is  broken  at  the  commencement. 

Seeing  that  all  the  end-organs  on  the  surface  of  the  body 
have  a  common  origin  morphologically,  it  would  be  reasonable 
to  expect  that  the  senses  would  have  much  in  common,  espe- 
cially when  these  organs  are  all  alike  connected  with  central 
nervous  cells  by  nerves.  As  a  matter  of  fact,  such  is  the  case, 
and  in  every  instance  we  can  distinguish  between  sensory  im- 
pulses generated  in  the  end-organ,  conveyed  by  a  nerve  inward, 
and  those  in  the  cells  of  these  central  nervous  systems,  giving 


timim 


tutummm 


550 


ANIMAL  PHYSIOLOGY. 


rise  to  certain  molecular  changes  which  enable  the  mind  or 
the  ego  to  have  a  perception  proper;  which,  when  taken  in  con- 
nection with  numerous  past 
experiences  of  this  and 
other  senses,  furnishes  the 
material  for  a  sensory  judg- 
ment. 

The  chief  events  are, 
after  all,  internal,  and  hence 
it  is  found  that  the  higher 
in  the  scale  the  animal 
ranks,  the  more  developed 
its  nervous  centers,  espe- 
cially its  brain,  and  the 
more  it  is  able  to  capitalize 
its  sensory  impulses;  also 
the  greater  the  degree  of 
possible  improvement  by 
Fio.  m.-v»wm  with  saaguon  odb  (O)  benerth  •  experience,  a  difference  well 
(^tfcJSmtST'^''""'**"''"'''*^  seen  in  blind  men  whose 

ability  to  succeed  in  life 
without  vision  is  largely  in  proportion  to  their  innate  and 
acquired  mental  powers.  Inasmuch  as  all  cells  require  rest, 
one  would  expect  that  under  constant  stimulation  fatigue  would 
soon  result  and  perceptions  be  imperfect.  Hence  it  happens 
that  all  the  senses  fail  when  exercised,  even  for  but  a  short  pe- 
riod, without  change  of  stimulus  leading  to  alteration  of  con- 
dition in  the  central  cells.  The  change  need  not  be  one  of  en- 
tire rest,  but  merely  a  new  form  of  exercise.  Hence  the  fresh- 
ness experienced  by  a  change  of  view  on  passing  through  beau- 
tiful scenery. 

Exhaustion  may  not  be  confined  wholly  to  the  central  ner  ^e- 
cells,  but  there  can  be  little  doubt  that  they  are  the  most  af- 
fected. Since  also  there  must  be  a  certain  momentum,  so  to 
speak,  to  molecular  activity,  it  is  not  surprising  that  we  find 
that  the  sensation  outlasts  the  stimulus  for  a  brief  period ;  and 
this  applies  to  all  the  senses,  and  necessarily  determines  the 
rapidity  with  which  the  successive  stimuli  may  follow  each 
other  without  causing  a  blending  of  the  sensations. 

Thus,  then,  in  every  sense  we  must  recognize  (1)  an  end- 
organ  in  which  the  chain  of  processes  begins ;  (2)  a  conducting 
nerve  through  which  (3)  the  central  nerve-cells  are  affected; 
and  we  may  speak,  therefore,  of  (1)  sensory  impulses  and  (2) 


THE  SKIN  AS  AN  OBOAN  OF  SENSK 


551 


the  mind  or 
taken  in  con- 
amerous  past 
if  this  and 
'umishes  the 
sensory  judg- 

events  are, 
lal,  and  hence 
it  the  higher 

the  animal 
ire  developed 
senters,  espe- 
lin,  and  the 
I  to  capitalize 
apulses;  also 
be  degree  of 
rovement  by 
lifferencewell 

men  whose 
cceed  in  life 
r  innate  and 

require  rest, 
fatigue  would 
ce  it  happens 
lut  a  short  pe- 
ration  of  con- 
,  be  one  of  en- 
nce  the  f  resh- 
;hrough  beau- 

sentralner^e- 
)  the  most  af- 
aentum,  so  to 
:  that  we  find 
if  period ;  and 
etermines  the 
y  follow  each 

18. 

se  (1)  an  end- 
I  a  conducting 
I  are  affected; 
julses  and  (2) 


sensations,  when  these  give  rise  to  affections  of  the  central 
nervous  cells  resulting  in  (1)  perceptions  and  (2)  judgments, 
when  we  take  into  account  the  psychic  processes ;  and,  from  the 
nature  of  cell-life  generally,  we  must  recognize  a  certain  inten- 
sity of  the  stimulus  necessary  to  arouse  a  sensation  and  a  limit 
within  which  alone  we  have  power  to  discriminate  (range  of 
stimulation  and  perception) ;  and  also  a  limit  to  the  rapidity 
wjith  which  stimuli  may  succeed  each  other  to  any  advantage, 
so  as  to  give  rise  to  new  sensations ;  and  a  limit  to  the  endur- 
ance of  the  apparatus  in  good  working  condition  corresponding: 
to  clear  mental  perceptions,  together  with  the  value  of  past  ex- 
perience in  the  interpretation  of  our  sensations. 


THE  SEIN  AS  AN  OBOAN  OF  SENSE. 

Bearing  in  mind  that  all  the  sensory  organs  originate  in 
the  ectoderm,  we  find  in  the  skin  even  of  the  highest  animals 
the  power  to  give  the  central  nervous  system  such  sense-im- 
pressions as  bear  a  relation  to  the  original  undifferentiated 
sensations  of  lower  forms  as  derived  from  the  general  surface 
of  the  body,  bat  with  less  of  specialization  than  is  met  with  in 
the  sense  of  hearing  and  vision ;  so  that  it  is  possible  to  under- 
stand how  it  is  that  the  skin  must  be  regarded  not  only  as  the 
original  source  of  sensory  impulses  for  the  animal  kingdom, 
but  why  it  still  remains  perhaps  the  most  important  source  of 
information  in  regard  to  the  external  world,  and  the  condition 
of  our  own  bodies ;  for  it  must  be  remembered  that  the  data 
afforded  for  sensory  judgments  by  all  the  other  senses  must 
be  interpreted  in  the  light  of  information  supplied  by  the  skin. 
We  really  perceive  by  the  eye  onlj-^  retinal  images.  The  dis- 
tance, position,  shape,  etc.,  of  objects  are  largely  determined  by 
feeling  them,  and  thus  associating  with  a  certain  visual  sensa- 
tion others  derived  from  the  skin  and  the  muscles,  which  latter 
are,  however,  generally  also  associated  with  Jactile  sensations. 

It  is  recorded  of  those  blind  from  birth  that,  when  restored 
to  sight  by  surgical  operations,  they  find  themselves  quite 
unable  to  interpret  their  visual  sensationis ;  or,  in  other  words, 
seeing  they  do  not  understand,  but  must  learn  by  the  other 
sens^,  especially  tactile  sensibility,  what  is  the  real  nature  of 
the  objects  that  form  images  on  their  retinae.  All  objects  seen 
appear  to  be  against  the  eyes,  and  any  idea  of  distance  is  out 
of  the  question. 


KMKIIWattllWllltW 


■MM 


mmmmt^' 


..j/IUMj.S^_iAJ_!ii.t'ai'3* 


552 


ANIMAL  PHTSIOLOOY. 


In  man  special  forms  of  end-organs  are  found  scattered  over 
tUe  skin,  mucous  and  serous  surfaces  of  the  body,  such  as 
Pacinian  corpuscles,  touch-corpuscles,  end-bulbs,  etc.  •  while  in 
lower  forms  of  vertebrates  many  others  are  found  in  parts 
where  sensibility  is  acute.  There  seems  to  be  little  doubt  that 
these  are  all  concerned  with  the  various  sensory  impulses  that 
originate  in  the  parts  where  they  are  found,  but  it  is  not  pos- 
sible at  present  to  assign  definitely  to  each  form  its  specific 
function. 

It  has  been  contended  that  the  various  specific  sensations 
of  taste,  as  bitter,  sweet,  etc.,  are  the  result  of  impulses  con- 
veyed to  the  central  nervous  system  by  fibers  that  have  this 
function,  and  no  other ;  and  a  like  view  has  been  maintained 
for  those  different  sensations  that  originate  from  the  skin. 
For  such  a  doctrine  there  is  a  certain  amount  of  support  from 
experiment  as  well  as  analogy ;  but  the  more  closely  the  subject 
is  investigated  the  more  it  appears  that  the  complexity  of  our 
sensations  is  scarcely  to  be  explained  in  so  simple  a  way  as 
many  of  these  theories  would  lead  us  to  believe.  Whether 
there  are  nerve-fibers,  with  functions  so  specific,  must  be  re- 
garded as  at  least  not  yet  demonstrated. 

Let  us  now  examine  into  the  facts.  What  are  the  different 
sensations,  the  origin  of  which  must  be  in  the  first  instance 
sought  in  the  skin,  as  the  impulses  aroused  in  some  form  of 
end-organ  or  nerve-termination  ? 

Suppose  that  one  blindfolded  lays  his  left  hand  and  arm 
on  a  table,  and  a  piece  of  iron  be  placed  on  the  palm  of  his 
hand,  he  may  be  said  to  be  conscious  of  the  nature  of  the  sur- 
face, whether  rough  or  smooth,  of  the  form,  of  the  size,  of  the 
weight,  and  of  the  temperature  of  the  body ;  in  other  words, 
the  subject  of  the  experiment  has  sensations  of  pressure,  of 
tactile  sensibility,  and  of  temperature  at  least,  if  not  also  to 
some  extent  of  muscular  sensibility.  But  if  the  right  hand  be 
used  to  feel  the  object  its  form  and  surface  characters  can  be 
much  better  appreciated;  while,  if  the  body  be  poised  in  the 
hand,  a  judgment  as  to  its  weight  can  be  formed  with  much 
greater  accuracy.  The  reason  of  the  former  is  to  be  sought  in 
the  fact  that  the  finger-tips  are  relatively  very  sensitive  in 
man,  and  that  from  experience  the  mind  has  the  better  learned 
to  interpret  the  sensory  impulses  originating  in  this  quarter ; 
which  again  resolves  itself  into  the  particular  condition  of  the 
central  nerve-ceUs  associated  with  the  nerve-fibers  that  convey 
inward  the  impulses  from  those  regions  of  the  skin.    Mani- 


THE  SKIN  AS  AN  ORGAN  OF  SENSE. 


653 


attered  over 
ly,  such  as 
c.  •  while  in 
ud  in  parts 
doubt  that 
apulses  that 
is  not  pos- 
its specific 

0  sensations 
ipulses  con- 
it  have  this 
.  maintained 
n  the  skin, 
ppport  from 
f  the  subject 
exity  of  our 
tie  a  way  as 
).  Whether 
must  be  re- 

}he  different 
irst  instance 
ome  form  of 

ad  and  arm 
palm  of  his 
3  of  the  sur- 
)  size,  of  the 
jther  words, 

pressure,  of 
'  not  also  to 
ight  hand  be 
cters  can  be 
Kxised  in  the 
Iwith  much 
i)e  sought  in 

sensitive  in 
etter  learned 
this  quarter ; 
dition  of  the 

1  that  convey 
skin.    Mani- 


festly if  there  be  a  sense  referable  to  the  muscles  (muscular 
sense)  at  all,  when  they  are  contracted  at  will  the  impression 
must  be  clearer  than  when  they  but  feebly  respond  to  the 
mere  pressure  of  some  body. 

It  is  possible,  as  every  one  knows,  to  attend  only  to  the  data 
afforded  by  one  set  of  impulses,  such  as  those  associated  with 
our  sensations  of  weight,  temperature,  etc.,  but  such  requires 
special  attention ;  and  as  in  the  case  of  the  eye  we  consider  the 
object  as  a  whole,  its  color,  form,  size,  anri  other  qualities,  so 
does  the  mind  form  its  complete  conception  by  a  synthesis  or 
union  of  a  variety  of  sensory  data.  Regarding  the  skin  as  a 
whole,  we  may  speak  of  the  skin-sense  as  we  do  of  the  ocular 
sense  or  vision.  The  separate  treatment  of  tactile,  thermal,  and 
other  forms  of  sensibility  under  sejurate  headings  is  a  matter 
of  convenience ;  but  there  is  considerable  danger  that  we  over- 
look the  great  fundamental  fact  that  our  knowledge  of  objects 
(is^rimarilg^^hetic  and  not_analytic.  True,  in  disease,  when 
one  or  more  sets  of  the  data  of  sense  as  derived  from  the  skin 
is  wanting,  the  others  can  be  appreciated,  and  these  alone. 
Nevertheless,  such  is  an  abnormal  condition,  and  in  that  case 
the  outer  world  passes  to  a  large  extent  beyond  the  degree  of 
control  natural  to  man.    ■ 

Patholffgiftri. — It  does  happen  in  certain  forms  of  disease, 
notably  of  the  spinal  cord,  that  tactile  sensibility  is  retained 
and  thermal  lost,  or  the  muscular  sense  impaired.  Such  per- 
sons are  plainly  reduced  at  once  to  the  condition,  not  only  of 
being  without  certain  sensory  impressions,  but  in  consequence 
unable  to  use  others  which  they  do  possess  to  the  same  extent 
as  before.  A  man  with  that  affection  of  the  spinal  cord  known 
as  locomotor  ataxy  may  have  tactile  and  thermal  sensibility, 
yet  be  unable  to  use  these,  in  the  absence  of  the  muscular  sense 
to  enable  him  to  be  his  own  master,  except  when  he  calls  in  the 
help  of  his  eyes,  as,  e.  g.,  in  walking. 

It  is  thus  seen  how  all  the  various  sources  of  information 
from  the  skin  and  muscles  blend  psychically  to  produce  a 
conception  which,  as  a  whole,  corresponds  to  "seeing."  The 
defects  just  referred  to  are  in  a  measure  comparable  to  color- 
blindn^s. 

With  this  warning  we  shall  now  attempt  to  state  some  of 
the  main  facts  in  regard  to  the  different  functions  of  the  skin 
as  a  sensory  or^n,  especially  endeavoring  to  trace  parallel  laws 
for  this  and  the  other  senses. 


■  ;-i(:v«:';'^-,'rt^i'- ■  '■ 


654 


ANIMAL  PHTSIOLOOr. 


PRESSUBB  Sensations. 

1.  There  is  a  relation  between  the  intensity  of  the  stimulus 
and  the  sensation  resulting,  and  this  limit  is  narrow.  The 
greater  the  stimulus  the  more  pronounced  the  sensation,  though 
ordinary  sensibility  soon  passes  into  pain.  Weber's  law  (to  be 
explained  later)  holds  in  the  case  of  the  skin  as  for  other  senses. 
2.  The  duration  of  the  sensation  is  very  brief.  It  is  said  that  a 
card  in  which  holes  have  been  punched,  so  that  when  in  rota- 
tion it  may  bear  on  the  skin,  may  be  made  to  touch  one  of  its 
holes  against  the  finger  as  often  as  fifteen  hundred  times  in  a 
second  before  the  sensations  are  fused.  3.  The  law  of  contrast 
may  be  illustrated  by  passing  the  finger  up  and  down  in  a  ves- 
sel containing  mercury,  when  the  pressure  will  be  felt  most  dis- 
tinctly at  the  point  of  contact  of  the  fluid.  4.  Pressure  is  much 
better  estimated  by  some  parts  than  others ;  hence  the  use  of  the 
tips  of  the  fingers  in  coimting  the  pulse,  palpating  tumors,  etc. 


Thermal  Sensations. 

1.  The  law  of  contrast  is  well  illustrated  by  this  sense ;  in 
fact,  the  temperature  of  a  body  exactly  the  same  as  that  of  the 
part  of  the  skin  applied  to  it  can  scarcely  be  estimated  at  alL 
The  first  plunge  into  a  cold  bath  gives  the  impression  that  the 
water  is  much  colder  than  it  seems  in  a  few  seconds  after,  when 
the  temperature  has  in  reality  changed  but  little ;  or,  perhaps, 
the  subject  may  be  better  illustrated  by  dipping  one  hand  into 
warmer  and  the  other  into  colder  water  than  that  to  be  ad- 
judged. The  sample  feels  colder  than  it  really  is  to  the  hand 
that  has  been  in  the  warm  water,  and  warmer  than  it  is  to  the 
other.  2.  The  limit  within  which  we  can  discriminate  is  at  most 
small,  and  the  nicest  determinations  are  made  within  about  27° 
and  33°  C. — i.  e.>  not  far  from  the  normal  temperature  of  the 
body.  3.  Variations  for  the  different  parts  of  the  skin  are 
easily  ascertained,  though  they  do  not  always  correspond  to 
those  most  sensitive  to  changes  in  pressure.  The  cheeks,  lips, 
and  eyelids  are  very  sensitive  to  pressure. 

fBecent  investigations  have  revealed  the  fact  that  there 
are  in  the  skin  "pressure-spots,"  and  "cold-spots "  and  "heat- 
spots"— i.  e.,  the  skin  may  be  mapped  out  into  very  minute 
areas  which  give  when  touched  a  sensation  of  pressure  differ- 
ent from  that  produced  by  the  same  stimulus  in  the  intermedi- 
ate regions ;  and  in  like  manner  are  there  areas  which  are  sen- 


e  stimulus 
row.  The 
on,  though 

law  (to  be 
bher  senses, 
said  that  a 
en  in  rota- 
I  one  of  its 

times  in  a 
of  contrast 
m  in  a  ves- 
It  most  dis- 
ire  is  much 
e  use  of  the 
amors,  etc. 


IS  sense ;  m 
that  of  the 
lated  at  alL 
on  that  the 
after,  when 
or,  perhaps, 
e  hand  into 
^t  to  be  ad- 

0  the  hand 

1  it  is  to  the 
e  is  at  most 
in  about  27* 
iture  of  the 
te  skin  are 
rrespond  to 
cheeks,  lips, 

that  there 
and  **heat- 
ery  minute 
jsure  differ- 
e  intermedi- 
dch  are  sen- 


THE  SKIN  AS  AN  ORGAN  OF  SENSE. 


555 


sitive  to  warm  and  to  cold  bodies  respectively,  but  not  to  both ; 
and  these  do  not  correspond  with  the  pressure-spots,  nor  to 
those  that  give  rise  when  touched  to  the  sensation  of  pain. 
These  spots  are  not  placed  symmetrically  on  both  sides  of  the 
same  individual,  nor  on  corresponding  parts  of  different  indi- 
viduals. So  much  has  been  ascertained  by  experiment.  It  is 
believed  by  some  of  the  investigators  that  these  areas  are  con- 
nected with  the  nerve-centers  by  nerve -fibers  devoted  to  con- 
ducting impulses  corresponding  to  the  sensations  which  have 
the  beginning  of  their  formation  in  the  different  kinds  of  spots. 
The  latter,  however,  has  not  been  demonstrated. 

C^hile  there  can  be  no  doubt  that  these  investigations  have 
furnished  additional  facts  of  great  importance,  they  can  not  be 
considered  as  making  the  whole  subject  of  sensation  by  the 
skin  perfectly  clear.  For  example,  how  are  we  to  explain  why 
a  cold  body  feels  heavier  than  a  warm  one,  as  may  easily  be 
demonstrated  to  one's  own  satisfaction  by  placing  a  large  coin 
cooled  down  to  near  the  freezing-point  on  the  forehead  beside 
a  warmer  one  ?  We  think  such  facts  are  calculated  to  enforce 
the  lesson  which  we  have  been  endeavoring  to  impress,  viz., 
that  our  sensations  are  never  single  (thermal,  tactile,  etc.),  but 
are  compound, one  or  the  other  element  preponderating;  and 
that  all  interpretations  of  sense  must  take  into  accoimt  this 
fact — ^and  the  very  important  one— that  every  sensory  impres- 
sion is  interpreted  in  the  light  of  our  past  experience,  as  well 
as  that  of  the  immediate  present. 

It  has  been  shown,  also,  that  the  extent  of  the  area  of  skin 
stimulated  determines  to  a  large  degree  the  quality  of  the  re- 
sulting sensation.  Thus,  the  temperature  of  a  fluid  does  not 
seem  the  same  to  a  finger  and  the  entire  hand.  This  fact  is  not 
irreconcilable  with  the  existence  of  the  various  kinds  of  ther- 
mal spots,  referred  to  above,  but  it  does  re-enforce  the  view  we 
are  urging  of  the  complexity  of  those  sensations  which  seem  to 
us  to  form  simple  wholes — as,  indeed,  they  do — just  as  a 
piece  of  cloth  may  be  made  up  of  an  unlimited  number  of 
different  kinds  of  threads. 

Tactile  Sensibility. 

As  a  matter  of  fact,  one  may  learn,  by  using  a  pair  of  com- 
passes, that  the  different  parts  of  the  surface  of  our  bodies  are 
not  equally  sensitive  in  the  discrimination  between  the  contact 
of  bodies — i.  e.,  the  judgment  formed  as  to  whether  at  a  given 


mUsmMmmm 


666  ANIMAL  PHYSIOLOGY. 

instant  the  skin  is  being  touched  by  one  or  two  points  is  de- 
pendent on  the  part  (. ".  the  body  with  which  the  points  are 
brought  into  contact. 

The  following  table  will  make  this  clear,  the  numbers  indi- 
cating the  distance  at  which  the  two  points  of  a  pair  of  com- 
passes must  be  apart  in  order  that  they  shall  not  give  rise  to 
the  judgment  of  one  point  of  contact,  but  be  recognized  as  two: 

XUIiiiMtrMk 

Tip  of  tongue VI 

Palm  of  last  phalanx  of  finger 2'2 

Palm  of  second  phalanx  of  finger 4*4 

Tip  of  nose 6*6 

Whitish  part  of  lips 8*8 

Back  of  second  phalanx  of  finger. 11*1 

Skin  over  malar  bone 15*4 

Back  of  hand 29*8 

Forearm 39*6 

Sternum 44*0 

Back 66*0 

There  seem  to  be  areas  of  skin  which  give  rise  when  pricked 
to  the  sensation  of  pain ;  but,  whether  we  should  distinguish  be- 
tween  tactile  and  pressuire  sensation  by  reference  to  correspond- 
ing spots,  does  not  yet  seem  clear. 

Certain  it  is  that  exercise  of  these  and  all  the  senses  greatly 
improves  them,  though  it  is  likely  that  such  advance  must  be 
referred  rather  to  the  central  nerve-cells  than  to  the  peripheral 
mechanism.  Careful  comparison  of  blind  and  seeing  children 
has  shown  that  the  blind,  in  forming  their  judgments,  appar- 
ently from  sensations  derived  through  the  skin,  in  reality  use 
much  collateral  help,  which  is  very  variable  and  certainly 
widely  different,  according  to  the  past  experience  and  general 
intelligence  of  the  individual. 

We  practically  distinguish  between  a  great  many  sensations 
that  we  can  neither  analyze  nor  describe,  though  the  very 
variety  of  names  suflGlces  to  show  how  much  our  interpretation 
of  sense  depends  on  past  experience. 

We  are  always  able  to  define  the  part  of  our  bodies  touched, 
and  with  great  accuracy,  no  doubt,  owing  to  the  simultaneous 
use  in  early  months  and  years  of  our  lives  of  vision  and  the 
senses  resident  in  the  skin. 

There  are,  however,  transient  illusions  of  sense  which  illus- 
trate the  remark  just  made.    If  a  small  marble  be  placed  be- 


^mmmmmmimmmmtmm 


THE  SKIN  AS  AN  OROAN  OF  SENSE. 


657 


oints  is  de- 
points  are 

nbers  indi- 
air  of  com- 
Bfive  rise  to 
zed  as  two: 


en  pricked 
inguish  he- 
orrespond- 

ses  greatly 
ce  must  be 
peripheral 
ig  children 
nts,  appar- 
reality  use 
L  certainly 
ad  general 

sensations 
1  the  very 
erpretation 

Bs  touched, 
nultaneous 
on  and  the 

rhich  illus- 
placed  be- 


tween the  radial  side  of  one  finger  and  the  ulnar  side  of  the 
other  (Aristotle's  experiment),  the  subject  of  the  experiment 
being  blindfolded,  it  will  be  judged  as  two  marbles  at  first, 
though  the  tactile  impression  is  soon  corrected,  especially  if  the 
eyes  be  opened.  These  surfaces  of  the  fingers  have  not  been 
accustomed  to  touch  at  the  same  time  the  one  body,  hence  the 
illusion. 

An  impression  made  on  the  trunk  of  a  nerve  is  referred  to 
the  peripheral  distribution  of  that  nerve  in  the  skin ;  thus,  if 
the  elbow  be  dipped  in  a  freezing  mixture,  the  skin  around  the 
joint  will  experience  the  sensation  of  cold,  but  a  feeling  of  pain 
will  be  referred  to  the  distribution  of  the  ulnar  nerve  in  the 
hand  and  arm.  The  same  principle  is  illustrated  by  the  com- 
mon experience  of  the  effects  of  a  blow  over  the  ulnar  nerve^ 
the  pain  being  referred  to  the  peripheral  distribution ;  also  by 
the  fact  that  pain  in  the  stump  of  an  amputated  limb  is  thought 
to  arise  in  the  missing  toes,  etc.     It  is  said  that  when  skin< 


transplanted  from  the  forehead  to  the  nose,  to  repair  missing, 


7 


parts,  is  touched,  the  sensation  is  located  in  the  original  site/ 
of  the  skin  (forehead).  In  all  such  facts  we  see  how  dependent/ 
are  all  our  sensory  judgments  on  our  past  experience,  illustrat- 
ing the  very  important  truth.  With  its  wide  ramifications,  that, 
in  a  physiological  sense,  as  well  as  in  many  others,  our^past_ 
makes  our  own  future  and  that  of  the  race  to  a  very  large 
e^ent^ 

The  Musculab  Sense. 

Every  one  must  be  aware  how  difficult,  it  is  to  regulate  his 
movements  when  the  limbs  are  cold  or  otherwise  deadened  in 
sensibility.  We  know  too  that,  in  judging  of  the  muscular 
effort  necessary  to  be  put  forth  to  accomplish  a  feat,  as  throw* 
ing  a  ball  or  lifting  a  weight,  we  judge  by  our  past  experi- 
ence. It  is  ludicrous  to  witness  the  failure  of  an  individual 
to  take  up  a  mass  of  metal  which  was  mistaken  for  wood.  In 
these  facts  we  recognize  that  in  the  successful  use  of  the  mus- 
cles we  are  dependent,  not  alone  on  the  sensations  derived  from 
the  skin,  but  also  from  the  muscles  themselves.  True,  the  mus- 
cles are  not  very  sensitive  to  pain  when  cut;  it  does  not,  how- 
ever, follow  that  they  may  not  be  sensitive  to  that  different 
effect,  their  own  contraction ;  whether  the  numerous  Pacinian 
bodies  around  joints,  or  the  end-organs  of  the  nerves  of  mus- 
cles are  directly  concerned,  is  not  determined. 

Ftthdogioal.— The  teaching  of  disease  is  plainly  indicative  of 


MM 


J 


5fi8 


ANIMAL  PHTSIOLOOY. 


the  importance  of  sensations  derived  both  from  the  skin  and 
the  muscles  for  co-ordination  of  muscular  movements. 

In  locomotor  ataxy,  in  which  the  power  of  muscular  co- 
ordination is  lost  to  a  large  extent,  the  lesions  are  in  the  pos- 
terior columns  of  the  spinal  cord,  or  the  posterior  roots  of  the 
nerves,  or  both,  and  these  are  the  parts  involved  in  the  trans- 
mission of  afferent  impulses. 

Whether  the  muscular  sense  also  implies  a  central "  neural " 
sense,  or  consciousness  of  the  changes  of  central  origin,  associ- . 
ated  with  the  execution  of  a  movement  as  distinct  from  the 
impressions  derived  from  the  muscles,  is  a  matter  of  dispute. 
But  the  student  will  be  already  prepared  for  our  answer  to  this 
question.  The  evidence  of  experiment  seems  to  point  to  a  dis- 
tinct source  of  information  in  the  muscles.  We  would  take 
along  with  this  the  additional  data  of  sense  afforded  by  the  skin, 
the  "sense  of  effort"  and  other  factors,  as  stored  past  experi- 
ence, which  must  be  very  variable  for  the  individual,  as  any 
one  may  observe  by  watching  the  muscular  efforts  of  others 
and  himself. 

OompuratiTe. — The  more  closely  the  higher  vertebrates  are 
observed,  the  more  convinced  does  one  become  that  those  sen- 
sory judgments,  based  upon  the  information  derived  from  the 
skin  and  muscles,  which  they  are  constantly  called  upon  to  form 
are  in  extent,  variety,  and  perfection  scarcely  if  at  all  surpassed 
by  those  of  man.  Of  course,  a  sensory  judgment  in  man,  with 
his  excessive  cerebral  development,  may  by  associations  in  his 
experience  be  worked  up  into  elaborate  judgments  impossible 
to  the  brutes,  but  we  now  refer  to  the  judgments  of  sense  in 
themselves. 

The  lips,  the  ears,  the  vibrissee  or  stiff  hairs,  especially 
about  the  lips,  the  nose,  in  some  cases  the  paws,  all  afford  deli- 
cate and  extensive  sensory  data. 

It  is  a  remarkable  fact  that  the  most  intelligent  of  the 
groups  of  animals  have  these  sensory  surfaces  well  developed, 
as  witness  the  elephant  with  his  wonderful  trunk,  the  hand 
of  the  monkey,  and  the  paws  and  vibrissfe  of  the  cat  and  dog 
tribe. 

On  the  other  hand,  the  groups  with  hoofs  are  notably  inferior 
in  the  mental  scale.  When  we  pass  to  the  lower  forms  of  in- 
vertebrates the  appreciation  of  vibrations  of  the  air  or  water 
in  which  they  live,  of  its  temperature,  of  its  pressure,  must  be 
considerable  to  enable  them  to  adapt  themselves  to  a  suitable 
environment. 


VISION. 


559 


)  skin  and 

iscular  co- 
ll the  pos- 
3ot8  of  the 
the  trans- 

1"  neural" 
l^n,  associ- . 
b  from  the 
of  dispute, 
wer  to  this 
nt  to  a  dis- 
irould  take 
)y  the  skin, 
ast  experi- 
iial,  as  any 
I  of  others 

)brates  are 
those  sen- 
1  from  the 
ion  to  form 
I  surpassed 
man,  with 
bions  in  his 
impossible 
of  sense  in 

,  especially 
afford  deli- 

ent  of  the 
developed, 
;,  the  hand 
sat  and  dog 

bly  inferior 
onus  of  in- 
dr  or  water 
re,  must  be 
a  suitable 


(We  have  not  spoken  of  sensations  derived  from  th-  internal 
organs  and  surfaces.  These  are  ill-defined,  and  we  know  them 
mostly  either  as  a  vague  sense  of  comfort  or  discomfort,  or  as 
actual  pain.  We  are  quite  unable  to  refer  them  at  present  to 
special  forms  of  end-organs.  They  are  valuable  as  reports  and 
warnings  of  the  animal's  own  condition. 

After-impressions  ("  after-images  ")  of  all  the  senses  referred 
to  exist,  mostly  positive  in  nature — i.  e.,  the  sensation  renfiains 
when  the  stimulus  is  withdrawn. 

SynoptiMl. — The  information  derived  from  the  skin  in  man 
and  the  other  higher  vertebrates  relates  to  sensations  of  press- 
ure, temperature,  touch,  and  pain.  The  muscles  also  supply 
information  of  their  condition.  In  how  far  these  are  referable 
to  certain  end-organs  in  the  skin  is  uncertain.  There  are  der- 
mal areas  that  give  rise  to  the  sensations  of  heat,  cold,  pressure, 
and  pain.  Whether  these  are  connected  with  nerve-fibers  that 
convey  no  other  forms  of  impulses  than  those  thus  arising  is 
undetermined. 

In  all  these  senses  the  laws  of  contrast,  duration  of  the  im- 
pression, limit  of  discrimination,  etc.,  hold. 

The  sensory  judgments  based  on  sensations  derived  from 
the  skin  are  syntheses  or  the  result  of  the  blending  of  many 
component  sensations  simultaneous  in  origin.  <^1  our  sensory 
judgments  are  very  largely  dependent  on  our  past  experience. 


VISION.^ 

Light  and  vision  are  to  some  degree  correlatives  of  each 
other.  Light  is  supposed  to  have  as  its  physical  basis  the  vibra- 
tions of  an  imponderable  ether.  Such  is,  however,  to  a  non- 
seeing  animal  as  good  as  non-existent,  so  that  we  may  look  at 
this  subject  either  with  the  eyes  of  the  physiologist  or  the  phys- 
icist, according  as  we  regard  the  cause  of  the  effects  or  the 
latter  and  their  relations  to  one  another..  It  is,  however,  im- 
possible to  understand  the  physiology  of  vision  without  a 
sound  knowledge  of  the  anatomy  of  the  eye,  and  an  apprehen- 
sion of  at  least  some  of  the  laws  of  the  science  of  optics.  The 
student  is,  therefore,  recommended  to  learn  practically  the 
coarse  and  microscopic  structure  of  the  eye  in  detail.  The  eyes 
of  mammals  are  sufficiently  alike  to  make  the  dissection  of  any 
of  them  profitable.  Bullocks'  eyes  are  readily  obtainable,  and 
from  their  large  size  may  be  used  to  advantage.    We  recom- 


>  ; 


tmrnm^im^^mm 


560 


ANIMAL  PHYSIOLOGY. 


Fio.  «».-Eye  tMrttally  diMctod  (atter  tepmjr).  1,  »Egg««TSi'.*iii'  k^^uh^MES^ 
bMk  io  M  fouBOOTw  the  choroid  oort ;  S.  oprnefc«HT|^  and  fo^^ 
ooM ;  «.  cauwl  of  Bchleinm ;  7,  external  nirfaoe  of  cborold,  travened  by  one  of  the  long 
ciUarr  •rteriee  and  br  olllarT  nenrea ;  8,  central  Tcaael,  into  which  the  vata  vortuoia 
^^ ;Tl«roh«old  loneTfi,  ciliary  netve. ;  18.  long  Hilary  aiteiy ;  18,  anterior  dllary 
artcdlea ;  14,  Iria ;  U,  Tawniiar  dnde  of  hia ;  16,  pupU. 

mend  one  to  be  boiled  hard,  another  to  be  frozen,  and  sections 
in  different  meridians  to  be  made,  especially  one  vertical  longi- 


-SUPERIOR  RECTUS 


m 


CHOROID 


OPTIC  NERVr 


CHOROID 


-INnRIORMBnW 
Fia.  MIt.— Section  of  human  eye,  aomewhat  diagrammatic  (after  Flint). 


VISION. 


S61 


tudinal  section.    Other  specimens  may  be  dissected  with  and 
without  the  use  of  water. 


■clerotio  dlHMted 
Mck  with  Mdarotie 
t>y  one  of  the  Iook 
b«  oata  vortieota 
IS,  anterior  cilUur 


and  sections 
Brtical  longi- 

ITUS 


-CHOROID 


IgPTtC  NERVr 


ROlO 


nw 

}T  Flint). 


ria.  «H.— Certain  parts  of  ere.  1 »  10.  (After  Sappejr.)  1, 1,  orjntaiUiw  tona ;  t,  hjralotd 
membrane ;  8, ■onule  of  Zlnn;  4,  iria;  S,  a  dUaoy  prooeaa;  t.radiatlns  libera  of  ciliary 
muscle ;  7,  section  of  droular  portion  of  ciliarjr  muscle ;  8,  venous  plenis  of  cUiarr  mus- 
cle; »,  10,  sclerotic  coat;  11,  IS,  cornea;  IS,  epithelial  lajrer  ol  come*;  14,  Descemefs 
membrane ;  15,  pectinate  Uitament  of  iris ;  16,  epitlielium  of  membrane  ot  Desoemec ;  17, 
union  of  sdMrotlo  coat  with  cornea ;  18,  section  of  canal  of  Bcfalwnm, 

Assuming  that  some  such  work  has  been  done,  and  that  the 
student  has  become  quite  familiar  with  the  general  structure 
of  the  eye,  we  call  attention  specially  to  the  strength  of  the 
sclerotic  coat ;  the  great  vascularity  of  the  choroid  coat  and  its 
terminal  ciliary  processes,  its  pigmented  character  adapting  it 
for  the  absorption  of  light ;  the  complicated  structure  and  pro- 
tected position  of  the  retinal  expansion.  It  may  be  said  that 
the  whole  eye  exists  for  the  retina,  and  that  the  entire  mechan- 
ism besides  is  subordinated  to  £he  formation  of  images  on  this 
nervous  expansion.  The  eye  of  the  mammal  may  be  regarded 
as  an  arrangement  of  refracting  media,  protected  by  coverings, 
with  a  window  for  the  admission  of  light,  a  curtain  regulating 
the  quantity  admitted ;  a  sensitive  screen  on  which  the  images 
are  thrown;  surfaces  for  the  absorption  of  superfluous  light; 

86 


iBiiiiiiWMniiiiinilMn 


562 


ANIMAL  PHYSIOLOGY. 


apparatus  for  the  protection  of  the  eye  as  a  whole,  and  for 
preserving  exposed  parts  moist  and  clean. 

Em'  ryologieaL — We  have  already  learned  that  the  first  indi- 
cation (.  '  the  eye  is  the  formation  of  the  optic  vesicle,  an  out- 
g^o^Hh  from  the  first  cerebral  vesicle.  This  optic  vesicle  be- 
comes more  contracted  at  the  base,  and  the  optic  stalk  remains 
as  the  oDtic  nerve. 


Fio.  laL 


Fia.  405. 


Fia.  406.— SecUon  ttiroiwfa  head  of  chick  on  third  day,  ahowing  orUrfn  of  eye  (after  Teo).  a, 
epiblast  undergoing  tUckeniiig  to  form  lena ;  o,  optic  n^hUe ;  v„  flrrt  cerebral  veeiole ; 
v.,  posterior  cerebral  Teaide.    It  will  be  observed  tliat  Uie  retina  is  alread;^  disUnotly  in- 

Fio.  406.— Later  stagos  in  development  of  eye  (after  Ctediat).  a,  epibUMt ;  c,  devd«>ping 
lens ;  o,  opUc  vesicle. 

At  an  early  stage  of  development  (second  or  third  day  in  the 
chick)  the  outer  portion  of  the  optic  vesicle  is  pushed  inward, 
so  that  the  cavity  is  almost  obliterated ;  the  anterior  portion, 
becoming  thickened,  ultimately  forms  the  retina  proper,  while 
the  posterior  is  represented  by  the  tesselated  pigment  layer  of 
the  choroid. 

As  this  retinal  portion  breaks  away  from  the  superficial  epi- 
thelium, the  latter  forms  an  elliptical  mass  of  cells,  the  future 
lens,  the  changes  of  which  in  the  formation  of  the  cells  peculiar 
to  the  lens  illustrate  to  how  great  lengths  differentiation  in 
structure  is  carried  in  the  development  of  a  single  organ.  It 
will  thus  be  seen  that  the  most  essential  parts  of  the  eye,  the 
optic  nerve,  the  retina,  and  the  crystalline  lens,  are,  according 
to  a  general  law,  the  earliest  marked  out.  The  cornea,  the  iris, 
the  choroid,  the  vascular  supply,  the  sclerotic,  etc.,  ere  all  sec- 
ondary in  importance  and  in  f onnation  to  these,  and  are  derived 
from  the  mesoblast,  while  the  essential  structures  are  traceable, 
like  the  nervous  system  itself,  to  the  epiblastic  layer. 


wwiiwiWi'fMaiiiwwwyiwiwJJirwtirjMwiw-aw  - 


'd  day  in  the 
ihed  inward, 
rior  portion, 
iroper,  while 
lent  layer  of 

perficial  epi> 
s,  the  future 
sells  peculiar 
'entiation  in 
le  organ.  It 
the  eye,  the 
:e,  according 
nea,  the  iris, 
,  are  all  seo- 
1  are  derived 
re  traceable. 


VISION. 


663 


Any  act  of  perfect  vision  in  a  mammal  may  be  shown  to 
consist  of  the  following :  (1)  The  focusing  of  rays  of  light  from 


Fio.  407.— More  adTanoed  ataM  o(  derdopaieiit  ot  eye  (after  Oardlat).  a,  epithelial  oeUa 
forminK  lens,  now  mwdi  anered :  b,  lena  capmie ;  e.  cotaneoaa  tianie  about  to  form  oon- 
JunctiTs ;  d,  e,  two  layers  of  optic  vMicle,  now  folded  back  and  (ormiiw  retina ;  /,  mucoua 
iiMue  forming  vitreous  humors ;  g,  interodlular  substanoe ;  k,  developiBK  optte  nerve ; 
i,  nerre-flbers  entering  rrthia. 

an  object  on  the  retina,  so  as  to  form  a  well-defined  image ;  (2) 
the  conduction  of  the  sensory  impulses  thus  generated  in  the 
retina  by  the  optic  nerve  inward  to  certain  centers ;  and  (3)  the 
elaboration  of  these  data  in  consciousness. 

We  thus  have  the  formation  of  an  image— a  physical  pro- 
cess; sensation,  perception,  and  judgment— physiological  and 
psychical  processes. 

In  the  natural  order  of  things  we  must  discuss  first  those 
arrangements  which  are  concerned  with  the  focusing  of  light 
i  e.,  the  formation  of  the  image  on  the  retinal  screen. 


DioPTBics  OF  Vision. 

One  of  the  most  satisfactory  methods  of  ascertaining  that 
the  eye  does  form  images  of  the  objects  in  the  field  of  vision 
is  to  remove  the  eye  of  a  recently  killed  albino  rabbit.    On 


rti:'«X'"-W.''*Wft  W 


Miijruinwiiifiiitrya- 


564 


ANIMAL  PHYSIOLOGY. 


holding  up  before  such  an  eye  any  small  .  Uject,  as  a  pair  of 
forceps,  it  may  be  readily  observed  that  an  inverted  image  of 
the  object  is  formed  on  the  back  of  the  eye  {fundus).  If,  how- 
ever, the  lens  be  removed  from  such  an  eye,  no  image  is  formed. 
If  the  lens  be  itself  held  behind  the  object,  an  inverted  image 
will  be  thrown  upon  a  piece  of  paper  held  at  a  suitable  (its 
focal)  distance.  By  substituting  an  ordinary  biconvex  lens,  the 
same  effect  follows.  It  thus  appears,  then,  that  the  lens  is  the 
essential  part  of  the  refracting  media,  though  the  aqueous  and 
vitreous  humors  and  the  cornea  are  also  focusing  mechanisms. 

The  fiurfaces  of  the  refracting  media  may  all  be  considered 
to  be  centered  on  one  of  the  axes,  which  meets  the  retina  above 
and  to  the  inner  side  of  the  fovea  centralis.  We  may  for 
practical  purposes  reason  from  a  diagrammatic  eye,  the  re- 
fracting surfaces  of  which  are  (1)  the  anterior  surface  of  the 
cornea,  (2)  the  anterior  surface  of  the  lens,  and  (3)  the  posterior 
surface  of  the  lens.  The  media  may  be  reduced  to  (1)  the  lens 
substance  and  {%)  the  aqueous,  or,  as  it  has  about  the  same 
refracting  power,  the  vitreous  humor. 

By  the  posderior  principal  focus  is  meant  the  point  at  which 
all  rays  that  fall  on  the  cornea  parallel  to  the  optic  axis  are 
focused.  It  is  14-647  mm.  behind  the  posterior  surface  of  the 
lens,  or  22*647  mm.  behind  the  anterior  surface  of  the  cornea  in 


Vm  408.— BBftmeUaB  br  mmm  teoMs  (after  rUnt  and  WeMMM).   The  !«>  mar  be  i  

tSwiJStotmmStSlmmS^tii  ligun),tat  Um  aalwoC  ■impUcity,  though  of  oouna 
this  to  aot  ■Metijr  aoounte. 


the  diagrammatic  eye.  In  the  actual  eye  the  fovea  of  the  retina 
must  occupy  this  position  when  at  rest,  if  a  distinct  image  is 
to  be  formed. 

It  will  appear  that  we  may  represent  the  eye  as  reduced  to 


"i»iff<>iw"Bm  iwjww-MiwwwiWI 


VISION. 


666 


as  a  pair  of 
ted  image  of 
8).  If,  how- 
a^  is  formed, 
rerted  image 
suitable  (its 
^ex  lens,  the 
e  lens  is  the 
aqueous  and 
aechanisms. 
le  considered 
retina  above 
Ne  may  for 
eye,  the  re- 
Lrface  of  the 
the  posterior 
a  (1)  the  lens 
ut  the  same 

nnt  at  which 
>ptic  axis  are 
urface  of  the 
the  cornea  in 


^ 


■U 


^ 


^.tlMNIghoC  OOUM 


k  of  the  retina 
tinct  image  is 

as  reduced  to 


the  lens  and  the  retina,  and  in  many  of  the  illustrations  to  fol- 
low this  will  be  done.  The  experiments  referred  to  above  will 
convince  the  student  that  such  is  the  case ;  and  we  may  here 
state  that,  while  the  various  principles  involved  in  the  physiol- ' 
ogy  of  vision  may  be  illustrated  in  great  perfection  by  elab- 
orate experiments,  we  shall  endeavor  to  supply  the  student 
with  accounts  of  very  simple  methods  of  convincing  himself 
by  personal  observation,  such  as  may  be  readily  repeaied  at  a 
future  time,  which  is  more  than  can  be  said  for  those  that  in- 
volve expensive  apparatus. 

Accommodation  of  the  Etb. 

Using  the  material  already  referred  to,  the  student  may 
observe  that,  with  the  natural  eye  of  the  albino  rabbit,  its  lens 
(or  better  that  of  a  bullock's  eye,  being  larger),  or  a  biconvex 
lens  of  glass,  there  is  only  one  position  of  the  instruments  and 
objects  which  will  produce  a  perfectly  distinct  image.  If  either 
the  eye  (retina),  the  lens,  or  the  object  be  shifted,  instead  of  a 
distinct  image,  a  blurred  one,  or  simply  diffuaion-cirdes,  appear. 

A  photographer  must  alter  either  the  position  of  the  object 
or  the  position  of  his  lend  when  the  focus  is  not  perfect.  The 
eye  may  be  compared  to  a  camera,  and  since  the  retina  and 
lens  can  not  change  position,  either  the  shape  of  the  lens  must 
change  or  the  object  assume  a  different  position  in  space.  As 
a  matter  of  fact,  any  one  may  observe  that  he  can  not  see 
objects  diatincUy  within  a  certain  limit  of  nearness  to  the  eye, 
known  as  the  near  point  (punctum  proximum) ;  while  he  be- 
comes conscious  of  no  effect  referable  to  the  eye  until  objects 
approach  within  about  sixty-five  to  seventy  yards.  Beyond 
the  latter  distance  objects  are  seen  dearly  without  any  effort. 
We  thus  learn  that  the  range  of  accommodation  lies  between 
about  five  inches  and  sixty  to  seventy  yards,  though  it  is  cus- 
tomary to  speak  of  the.  far  point  as  infinity  («),  which  simply 
means  that  the  rays  from  objects  beyond  the  distance  given 
above  are  practically  parallel,  and  are,  therefore,  focused  on 
the  retina  without  any  alteration  in  the  shape  of  the  lens  {neg- 
aiive  aecommodation) ;  while  nearer  onds  require  this.  When 
objects  are  nearer  to  the  eye  than  about  five  inches,  for  most 
persons,  the  eye  can  not  accommodate  sufficiently  to  bring  the 
rays  of  light  emanating  from  them  to  a  focus  on  tlie  retina. 

There  are  many  ways  in  which  we  may  be  led  to  realize 
these  truths :  1.  When  one  is  reading  a  printed  page  it  is  only 


.3 


566 


ANIMAL  PHTSIOLOOT. 


the  very  few  words  to  which  the  eyes  are  then  specially  di- 
rected that  are  seen  clearly,  the  rest  of  the  page  appearing 
blurred ;  and  the  same  holds  for  the  objects  in  any  small  room. 
We  speak  of  picking  out  an  acquaintance  in  an  audience  or 
crowd,  which  implies  that  each  of  the  individuals  composing 
the  throng  is  not  distinctly  seen  at  the  same  time.  2.  If  an  ob- 
server hold  up  a  finger  before  his  eyes,  and  direct  his  gaze  into 
the  distance  (relax  his  accommodation),  presently  he  will  be- 
hold a  second  shadowy  finger  beside  the  real  one — i.  e.,  he  sees 
double :  his  eyes,  being  accommodated  for  the  distant  objects, 
can  not  adapt  themselves  at  the  same  time  for  near  ones.  3.  The 
principle  involved  may  be  most  precisely  illustrated  by  Schein- 


!   -A 


Ito.  4n.— Dtasnunto 
oate  tha  oimmmiUuMea 


SdMiner'a     , 
wlilobthera 


It  (after  LMidois).    The  dotted  linep  indi- 
double  Tlaion. 


».  410.— Tte wwleto 8dtBliiet»e wrperimeiit (elter Peraeteto).  tlieoMMttaet  a:  thehiMia 
wpwentedV  6;  and  the  retfaia  mair  Im  at  m,  m,  n.H,  or  1,1.   Am  card  with  ita  holM. 
c/todirMSttartaifrMitortbeleiia.   It  la  plain  Oat,  if  tiiennriiatrike  the  retina  in  anjr  way 
•j"  _.  __  ."v ...  ..  .  ...-...-  .—jrrrr.^  w.  (omllJS,   ona  or  other  of  theae  wiU 

>  oardiaatopped;  whioh  of  tbem  will 


eaioept  aa  repreaanted  at  e,  double  imama  muat  be 
diaMMear  aooordinc  aa  the  right  or  left  kola  of  the 
dependw  olroanaBmea-i.  e.,  aa  to  whaOMT  tha  cai 


caaa  ia  that  flgured  at  «»,  m  orl,  i. 


ii»iiliii»MiiiiiWiiWHi'iiiim"i'wi<i>ii'mni»Mi 


VISION. 


667 


ipecially  di- 
I  appearing 
jmall  room, 
iudience  or 
composing 
2.  If  an  ob- 
is gaze  into 
he  will  be- 
L  e.,  he  sees 
Etnt  objects, 
aes.  3.  The 
L  by  Schein- 


dottedUnepiiidl- 


»       / 


lata:  the  lent  to 
rd  wtai  it*  holM, 
retina  in MijrwMr 
theroftlMMwdl 
rhtohoftbemwUI 
m,  t»  or  {,  i. 


er's  experiments  (Figs.  409  and  410).  Let  two  small  holes  be 
pricked  in  a  card,  at  a  distance  from  each  other  not  greater 
than  the  diameter  of  the  pupil ;  fix  the  card  upright  on  a  piece 
of  board,  about  two  feet  long,  and,  closing  one  eye,  observe  the 
effect  of  looking  at  two  pins  stuck  into  the  board  in  line  with 
each  other,  at  different  distances  apart.  It  may  be  observed  that 
as  soon  as  the  nearest  pin  is  approximated  to  the  card  within 
a  certain  distance  it  fails  to  be  distinctly  seen,  and  appears 
double — ^i.  e.,  the  near  point  is  exceeded ;  that  when  the  distant 
pin  is  in  focus,  the  near  one  appears  double,  and  vice  versa. 
When  the  image  is  double,  blocking  one  of  the  two  holes 
causes  one  image  to  disappear,  and  this  is  the  right  or  the  left 
hand  image,  according  as  the  one  or  the  other  hole  is  stopped, 
and  as  it  is  the  distant  or  near  pin  that  is  seen  as  two.  The 
reason  of  this  will  be  plain  from  the  above  figures,  but  it  must 
be  remembered  that  an  image  on  the  right  of  the  retina  is  ad- 
judged to  be  on  the  left  of  the  visual  field,  as  will  be  explained 
later. 

In  what  does  accommodation  consist  ?  If  light  from  a  can- 
dle or  lamp  be  allowed  to  fall  obliquely  on  the  eye  of  a  second 
person,  through  a  card  on  which  two  triangular  holes  have 
been  cut  one  above  the  other,  three  pairs  of  images  of  the  flame 
(necessarily  triangular)  may  be  seen  reflected  from  the  eye  of 
the  observed  subject,  two  of  which  are  erect  and  one  inverted; 
the  brightest  and  most  distinct  being  from  the  cornea,  the  sec- 
ond pair  dimmer  and  larger  from  the  anterior  surface  of  the 
lens,  and  the  smallest  (c)  from  the  posterior  surface  of  the  lens, 
inverted,  since  it  is  produced  by  a  concave  mirror.  When  the 
subject  of  the  observation 
looks  at  a  near  object,  only 
one  of  these  pairs  of  images 
alters  appreciably,  viz.,  that 
from  the  anterior  surface  of 
the  lens,  the  middle  pair  (b). 
The  conclusion  then  follows 
that  accommodation  consists 
essentially  in  an  alteration  of 
the  convexity  of  the  anterior  surface  of  the  lens.  The  images 
appear  nearer  to  each  other  the  more  convex  the  lens  becomes. 
Without  the  help  of  a  special  instrument  (phakoscope)  the  ob- 
server may  fail  to  see  the  change,  though  that  the  other  pairs 
da  not  alter  position  or  size  he  may  certainly  readily  observe. 

This  change  in  the  shape  of  the  lens  is  accomplished  as 


411.— PurUnJe'i  inwRcs.    a  h  e  during 
"ra,  o,  N  e,  dorinf  porittra  aocoamo- 


668 


ANIMAL  PHYSIOLOGY. 


follows :  The  lens  is  naturally  very  elastic  and  is  kept  in  a  par- 
tially compressed  condition  by  its  capsule,  to  which  is  attached 
the  suspensory  ligament  which  has  a  posterior  attachment  to 
the  choroid  and  ciliary  processes.    When  the  ciliary  muscle. 


Ite.  41S.— niuatntM  meohuim  of  Meominodation  (after  Viclo.   The  left  tU» 
relation  of  parte  duriiur  the  paMtre  oonditioii  of  the  ere  (negative  «« 
t  for  long  dirtanoea) ;  the  rli^t  aide,  that  fornear  objeota. 


the 
ktion,  or 


which  operates  from  a  fixed  point  the  comeo-sclerotic  junction, 
pulls  upon  the  choroid,  etc.,  it  relaxes  the  suspensory  ligament ; 
hence  the  lens,  not  being  pressed  upon  in  front  as  it  is  from 
behind  by  the  vitreous  humor  (invested  by  its  hyaloid  mem- 
brane), is  free  to  bulge  and  so  increase  its  refractive  power. 
The  nearer  an  object  approaches  the  eye,  the  greater  the  diver- 
gence of  the  ray^  of  light  proceeding  from  it,  and  hence  the 
necessity  for  greater  focusing  power  in  the  lens. 

If  a  person  be  observed  closely  when  looking  from  a  remote 
to  a  near  object,  it  may  be  noticed  that  the  eyes  turn  inward — 
i  e.,  the  visual  axes  converge  and  the  pupils  contract.  These 
are  not,  however,  essential  in  the  sense  in  which  the  changes 
in  the  lens  are ;  for,  as  before  stated,  in  the  absence  of  the  lens 
distinct  vinon  is  quite  impossible.  Were  additional  evidence 
necessary  to  show  that  accommodation  is  effected  as  described, 
it  might  be  st&ted  that  by  stimulation  of  the  lenticular  gan- 
glion the  ciliary  muscle  may  in  an  animal  thus  experimented 
upon  be  shown  to  contract,  the  choroid  to  be  drawn  forward, 
and  the  anterior  convexity  of  the  lens  to  be  increased.  Vaso- 
motor changes  or  alterations  in  the  size  of  the  iris,  if  they  have 
any  effect  upon  the  lens  at  all,  must  play  a  very  unimportant 
pari  The  movements  of  the  iris  do,  however,  serve  an  impor- 
tant purpose,  and  to  that  subject  we  now  turn. 


»a»w»Wpg«|Mj!|WiMigl!iti'JWWW»-tWiW|ilWP».iaaitl-fllB.W.M^^ 


■v-v.-.v-  ■'  ••  '-^TVfrii 


pt  in  a  par- 
is  attached 
ochment  to 
Etry  muscle. 


M0  depioto  the 
oommomtion,  or 


ic  junction, 
y  ligament; 
B  it  is  from 
aloid  mem- 
tive  power. 
ir  the  diver- 
d  hence  the 

>m  a  remote 
m  inward — 
■act.  These 
the  changes 
of  the  lens 
lal  evidence 
bs  described, 
ticular  gan- 
cperimented 
mi  forward, 
hsed.  Vaso- 
if  they  have 
inimportant 
'^e  an  impor- 


VISION. 


see 


Altkrations  in  the  Size  of  the  Pupil. 


The  pupil  varies  in  size  according  as  the  iris  is  in  a  greater 
or  less  degree  active.  All  observers  are  agreed  that  the  circu- 
lar fibers  around  the  pupillary  margin  are  muscular,  forming 
the  so-called  sphincter  of  the  iris ;  but  great  differences  of  opin- 
ion still  exist  in  regard  to  the  radiating  fibers.  It  is  thought 
by  many  that  all  the  changes  in  the  iris  may  be  explained  by 
the  elasticity  of  its  structure  without  assuming  the  existence 
of  muscular  fibers  other  than  those  of  the  sphincter;  thus  a 
contraction  of  the  latter  would  result  in  diminution  of  the  pu- 
pillary aperture,  its  relaxation  to  an  enlargement,  provided  the 
rest  of  the  iris  were  highly  elastic. 

The  conclusions  in  regard  to  the  innervation  of  the  iris  rest 
largely  upon  the  results  of  certain  experiments  which  we  shall 


OpUceentn- 


Oetiio-motor.^ i. 

eentre  \         •»^ 


DOator 


'^^r-ib'sr-^'K^vmsMX.-i 


ArnipatMIe  tunw  to 
mMoMna/ibnt 


fiiplnal  Motor  Mtitfv 


Vn.  4U.-1>iMnun  to  Uhutnte  tenemtloB  of  Uw  irto.   Dotted  Udm  indloirte  geami  (Bno- 
«lo5>looiiBeetton(oorreleaon>.    Coune  a(  imiNilMi  indicaied  Iqr  wrows. 


570 


ANIMAL  PHYSIOLOGY. 


now  briefly  detail :  1.  When  the  third  nerve  is  divided,  stimu- 
lation of  the  optic  nerve  (or  retina)  does  not  cause  contraction 
of  the  pupil  as  usual.  2.  When  the  optic  nerve isdivided, light 
no  longer  causes  a  contraction  of  the  pupil,  though  stimulation 
of  the  third  nerve  or  its  center  in  the  anterior  portion  of  tho 
floor  of  the  aqueduct  of  Sylvius  does  bring  about  this  result. 
3.  Section  of  the  cervical  sympath^ttic  is  followed  by  contrac- 
tion and  stimulation  of  its  peripheral  end  by  dilation  of  the 
pupil. 

From  such  experiments  it  has  been  concluded  that — 1.  The 
optic  is  the  afferent  nerve  and  the  third  nerve  the  efferent  nerve 
concerned  in  the  contraction  of  the  pupil ;  and  that  the  center 
in  the  brain  is  situated  as  indicated  above,  so  that  the  act  is  or- 
dinarily a  reflex.  2.  That  the  cervical  sympathetic  is  the  path 
of  the  efferent  impulses  regulating  the  action  of  the  radiating 
fibers  of  the  iris. 

Its  center  has  been  located  near  that  for  the  contraction  of 
the  piipil,  and  it  may  be  assumed  to  exert  a  tonic  action  over 
the  iris  comparable  to  that  of  the  vaso-motor  center  over  the 
blood-vessels. 

The  impulses  may  be  traced  through  the  cervical  sympa- 
thetic and  its  ganglia  back  to  the  first  thoracic  ganglion,  and 
thence  to  the  spinal  cord  and  brain.  There  may  be  subsidiary 
centers  in  the  cervical  spinal  cord. 

There  are  facts  which  it  is  difficult  to  explain  in  the  above 
manner.  Thus,  whdn  atropin  is  dropped  into  the  eye,  the  dila- 
tation is  greater  than  that  which  follows  section  of  the  optic 
nerve  or  the  third  nerve.  In  such  a  case,  paralysis  of  the  con- 
tracting mechanism,  by  which  the  dilating  mechanism  is  left 
free  to  act,  should  produce,  we  might  suppose,  the  greatest  pos- 
sible dilation  of  the  pupil,  especially  if  we  assume,  as  some  do, 
that  there  are  no  radiating  muscular  fibers,  but  that  all  the 
,  effects  are  produced  through  the  sphincter  of  the  iris ;  but  such 
is  not  the.  case.  The  result  has  been  set  down  to  the  action  of 
the  drug  upon  a  local  nervous  mechanism,  or  the  muscular 
fibers  themselves,  or  to  the  v^so-motor  changes  said  to  be  co- 
incident. This  view  is  strengthened  by  the  fact  thai  stimu- 
lation of  the  retina  'in  a  recently  removed  eye  will  cause  some 
reflex  contraction  of  the  pupil.  In  explaining  the  action  of 
drugs  on  the  pupil  we  are  not  limited  to  either  a  purely  local 
or  a  purely  central  influence ;  some  seem  to  act  in  one  stage 
more  upon  the  centers,  in  another  more  locally.  Vaso-motor 
influences  undoubtedly  do  affect  the  size  of  the  pupil,  full  vessels 


Bi«i»mi»iiwiiiiiii»iii.i  jii.iijim».ij.i)i.u..  wnwuBWHui.u  j>i>wj»w#)»itwMWtuiuii>wa«i»>a'ij»!groagaiBaia^ 

1/ 


VISION. 


671 


ided,  stimu- 
contractioit 
vided,  light 
stimulation 
rtion  of  tho 
this  result, 
by  contrac- 
ition  of  the 

lat— 1,  The 
erent  nerve 
t  the  center 
le  act  is  or- 
is the  path 
le  radiating 

itraction  of 
action  over 
ter  over  the 

Leal  sympa- 
oiglion,  and 
)  subsidiary 

n  the  above 
ye,  the  dila-  * 
)f  the  optic 
I  of  the  con- 
aism  is  left 
reatest  pos- 
as  some  do, 
ihat  all  the 
B ;  but  such 
lie  action  of 
e  muscular 
d  to  be  co- 
thai  stimu- 
cause  some 
e  action  of 
lurely  local  ' 
i  one  stage 
Vaso-motor 
full  vessels 


tending  to  contraction  and  the  reverse  to  dilation.  Upon  the 
whole,  it  seems  best  to  regard  the  two  mechanisms  as  supple- 
mentary to  one  another,  so  that  usually  with  increased  action 
of  the  one  there  is  diminished  action  of  *he  other.  We  find 
that  the  twO  eyes  move  in  harmony,  and  v  .t  the  two  pupils  in 
health  are  always  of  the  same  size.  Light  thrown  upon  one 
eye  contracts  the  pupil  of  the  other.  We  are  thus  led  to  be- 
lieve in  associated  or  consensual  movement  of  the  iris,  owing 
to  nervous  connections  between  the  various  centers  involved. 
These  are  physiological,  but  whether  anatomical  or  not,  in  the 
sense  that  annectant  fibers  exist,  is  tmcertain ;  and,  however, 
in  the  evolution  of  function,  they  may  have  been  at  first  pro- 
duced, have  been  so  strengthened,  according  to  the  law  of  habit, 
that  now  it  is  with  the  greatest  difficulty  that  one  may  learn 
to  move  one  eye  independently  of  the  other,  or  modify  the 
form  of  the  pupils  without  also  shifting  the  visual  axes. 

It  is  to  be  remembered  that,  although  the  dilating  center  is 
automatic  in  action,  it  may  also  act  reflexly,  oi:  be  modified  by 
unusual  afferent  impulses — ^as,  e.  g.,  the  strong  stimulation  of 
any  sensory  nerve  which  causes  enlargement  of  the  pupil 
through  inhibition  of  the  center.  To  render  the  paths  of 
impulses  affecting  the  iris  somewhat  clearer,  it  is  well  to  bear 
in  mind  the  nervous  supply  of  the  part :  1.  The  third  nerve, 
through  the  ciliary  (ophthalmic,  lenticular)  ganglion,  supplies 
short  ciliary  nerves  to  the  iris,  ciliary  muscle,  and  choroid.  2. 
The  cervical  sympathetic  reaches  the  iris  chiefly  through  the 
long  ciliary  nerves  and  the  ophthalmic  division  of  the  fifth. 
3.  There  are  sensory  fibers  from  the  fifth  nerve ;  and,  according 
to  some  observers,  also  dilating  fibers  from  this  nerve  inde- 
pendent of  the  sympathetic,  as  well  as  those  that  may  reach 
the  eye  by  the  long  ciliary  nerves  without  entering  the  ciliary 
ganglion.  4.  The  centers  from  which  both  the  contracting  and 
dilating  impulses  proceed  are  situated  near  to  each  other  in 
the  floor  of  the  aqueduct  of  Sylvius.  It  is  of  practical  im- 
portance to  remember  the  various  circumstances  under  which 
the  pupil  contracts  and  dilates. 

Contradion  (Myosis).  —  1.  Access  of  strong  light  to  the 
retina.  2.  Associated  contraction  on  accommodation  for  near 
objecta  3.  Similar  associated  contraction  when  the  visual  axes 
converge,  as  in  accommodation  for  near  objects.  4.  Reflex 
stimulation  of  afferent  nerves,  as  the  nasal  or  ophthalmic  divis- 
ion of  the  fifth  nerve.  6.  During  sleep.  6.  Upon  stimulation 
of  the  optic  or  the  third  nerve,  and  the  corpora  quadrigemina 


J 


mmm 


672 


ANIMAL  PHTSIOLOOT. 


or  adjacent  parts  of  the  brain.  7.  Under  the  effects  of  certain 
drugs,  as  physostigmin,  morphia,  etc. 

DiUUion  {Mydriasis). — 1.  In  darkness,  i.  On  stimulation 
of  the  cervical  sympathetic.    8.  During  asphyxia  or  dyspnoea. 

4.  fiy  painful  sensations  from  irritation  of  peripheral  parts. 

5.  From  the  action  of  certain  drugs,  as  atropin,  etc.  The 
student  may  impress  most  of  these  facts  upon  his  mind  by 
making  the  necessary  observations,  which  can  be  readily  done. 

PitholofisaL— As  showing  the  importance  of  such  connec- 
tions, we  may  instance  the  fact  that,  in  certain  forms  of  nervous 
disease  (e.  g.,  locomotor  ataxia),  the  pupil  contracts  when  the 
eye  is  accommodated  to  near  objects,  but  not  to  light  (the 
Argyll-Robertson  pupil).  In  other  cases,  owing  to  brain-dis- 
ease, the  pupils  may  be  constantly  dilated  or  the  reverse ;  or 
one  may  be  dilated  and  the  other  contracted. 

Optical  Impkbfbctionb  or  the  Eye. 

The  defects  to  be  noticed  now  ire  common  to  all  human 
eyes,  and  probably  to  the  eyes  of  eXi.  mammals,  though  in 
some  persons  certain  of  them,  as  astigmatism,  are  of  so  serious 
a  character  that  they  require  special  remedies. 

J^^hniMl  AbmmUoB.— The  nature  of  this  defect  may  be  best 
learned  from  an  examination  of  Fig.  414,  below.  It  will  be 
seen  that  rays  of  light  passing  through  the  lens  are  brought  to 


b  li  Mt  pWflMStlr  riMVPtr 


l»tatm»Atta,8, 


a  focus,  varjring  with  the  point  of  the  lens  through  which  they 
pass,  the  focusing  power  of  any  ordinary  convex  lens  being 
greater  toward  the  circumference.  This  defect  is  believed  to 
be  corrected  in  the  human  eye,  at  least  to  some  extent,  by  the 
following: 

1.  The  iris  cute  off  the  more  strongly  refracted  outer  rays. 
2.  The  corneal  curvature  is  rather  ellipsoidal,  so  that  those 
rays  farthest  from  the  optical  axis  are  least  deviated  by  it. 
8.  The  anterior  and  posterior  curvatures  of  the  lens  are  cor- 
rective of  each  other.    4.  The  power  of  refraction  of  the  lens 


n*Mi 


RMn 


mmm 


i 


VISION. 


578 


ts  of  certain 

stimtilation 
or  dyspnoea, 
theral  parts. 
1,  etc.  The 
lis  mind  by 
readily  done, 
inch  connec- 
ts of  nervous 
ts  when  the 

0  light  (the 
to  brain-dis- 

1  reverse:  or 


o  all  human 
I,  though  in 
of  so  serious 

may  behest 
.  It  will  be 
ne  brought  to 


(•bfonnwIitSiS, 

h  which  they 
IX  lens  being 
B  believed  to 
ixtent,  by  the 

)d  outer  rays, 
lo  that  those 
mated  by  it. 
lens  are  cor- 
>n  of  the  lens 


does  not  increase  regularly  from  the  c^i uter  to  th    cirownf  '' 

ence. 

ArtiffBMtifB. — In  this  defect  the  vertical  meridian  Ih  ,>- 
posed  to  be  more  convex  than  the  horizontal,  as  is  partJ  iy 
the  case  with  the  cornea  of  the  eye,  and  it  is  to  this  body  t^it 
astigmatism  is  usually  referable,  rather  than  to  the  lens,  though 
the  latter  may  also  be  clefective. 

In  astigmatism,  when  a  vertical  line  is  in  focus  a  horizontal 
can  not  be  distinctly  seen,  and  the  reverse.  This  any  one 
may  readily  demonstrate  to  himself  by  drawing  one  straight 
line  at  right  angles  to  the  center  of  another  and  looking  at  the 
figure ;  when  the  one  is  seen  distinctly,  the  other  is  blurred.  It 
is  to  be  borne  in  mind  that,  in  order  to  see  a  horizontal  line 
distinctly,  it  is  of  most  importance  that  the  rays  that  diverge 
from  this  line,  in  a  series  of  vertical  planes,  be  well  focused, 
rather  than  those  which  diverge  in  the  plane  of  the  line  itself ; 
so  that,  when  the  cornea  is  most  curved  in  the  vertical  meridian, 
a  horizontal  line  will  be  represented  by  an  image  of  a  horizontal 
line  at  the  nearer  focus—i.  e.,  when  the  vertical  is  the  most  con- 
vex meridian,  horizontal  lines  are  soonest  focused,  and  this 
holds,  in  fact,  of  most  eyes. 

When  the  astigmatism  affects  several  meridians, "  irregular 
astigmatism  "  results. 

The  defect  in  question  is  to  be  corrected  by  glasses  made  of 
sections  of  a  cylinder,  thickest  in  the  region  corresponding  to 
that  of  greatest  corneal,  etc.,  dbfect. 

duromatie  Abenratton. — In  the  figure  below,  in  which  7i  A  rep- 
resents the  lens,  it  will  be  seen  that  the  violet  and  red  rays 
have  different  foci,  so  that,  when  the  eye  is  accommodated  for 
the  one  set  of  rays,  the  others  are  seen  indistinctly.    Assuming 


Ito.  4l&-I)lNltam  to  OhMlntochraaMUe  aiiamtion  (aflMT  1^^ 

that  the  retina  is  at/,  the  rays  will  be  blended ;  but  if  between 
Fand/,  or/  and  U,  the  blue  center  will  have  a  red  circumfer- 
ence, and  the  reverse  respectively. 

As  the  focal  distances  for  near  objects  differs  so  little  usual- 
ly, this  defect  is  not  observed  by  us ;  but  it  may  be  made  ob- 


674 


ANIMAL  PHYSIOLOGY. 


\ 


muB  by  looking  at  a  flame  through  cobalt-blue  glass,  which 
allows  only  the  red  and  blue  rays  to  pass :  the  flame  may  appear 
red  surrounded  by  blue  or  blue  surrounded  by  red,  according 
to  the  character  of  the  accommodation  of  the  eye  at  the  time. 
Since  the  eye  has  to  be  accommodated  for  violet  (see  Fig.  415) 
more  than  blue,  bodies  of  equal  size,  red  in  color,  always  appear 
nearer  than  violet  ones.  Hence,  also,  it  is  difficult  to  see  the 
red  and  violet  gf  the  speqtrum  with  equal  distinctness  at  the 
same  time. 

Intoptie  ThmooMiia. — Opaque  bodies  in  any  of  the  media  of 
the  eye  may  cast  shadows  on  the  retina. 

When  movable,  as  they  often  are  in  the  vitreous  humor, 
they  are  known  as  mumxB  voliiantea,  from  their  fancied  resem- 
blance to  gnats. 

One  looking  through  a  microscope  is  apt  at  first  to  see  what 
does  not  exist,  apart  from  his  own  eye,  owing  to  various  forms 
of  the  nature  now  referred  to,  but  which  may  be  distinguished 
from  real  objects  by  the  inability  to  fix  them  in  the  field  of 
vision,  for  as  soon  as  the  attempt  is  made  they  vanish. 

Tears  on  the  cornea  and  other  inequalities  from  foreign 
bodies,  pressure,  etc.,  likewise  give  rise  to  such  phenomena. . 

An  interesting  little  experiment,  which  illustrates  both  the 
alterations  in  size  of  one's  own  pupils  with  the  amount  of  light, 
and  at  the  same  time  irregularities  in  their  margins,  if  they 
exist,  may  be  thus  carried  out :  Let  a  pin-hole  be  pricked  in  a 
card,  and,  holding  this  close  to  the  eye,  look  at  a  light  or  a 
bright  surface.  On  opening  and  closing  the  other  eye  the 
changes  in  the  size  of  the  pupil  of  the  first  eye  may  be  seen 
to  alter  with  the  amount  of  light  admitted  to  the  second — i.  e., 
the  field  of  view  is  alternately  diminished  and  increased. 

AnomaliM  of  Befiractioa. — 1.  We  may  speak  of  an  eye  in  which 
the  refractive  power  is  such  that,  under  the  limitations  referred 
to  before  (page  564),  images  are  focused  on  the  retina,  as  the 
emmetropic  eye.  The  latter  is  illustrated  by  Fig.  416.  In  the 
upper  figure,  in  which  the  eye  is  represented  as  passive  (nega- 
tively accommodated),  parallel  rays— i.  e.,  rays  froija  objects 
distant  more  than  about  seventy  yards  (according  to  some 
writers  much  less)— are  focused  on  the  retina ;  but  those  from 
objects  near  at  hand,  the  rays  from  which  are  divergent,  are 
focused  behind  the  retina.  In  the  lower  figure  the  lens  is  rep- 
resented as  more  bulging,  from  accommodation,  as  such  diver- 
gent rays  are  properly  focused. 

2.  In  the  myopic  (near-sighted)  eye  the  parallel  rays  cross 


•mmm 


glass,  which 
)  may  appear 
)d,  according 
I  at  the  time, 
see  Fig.  415) 
[ways  appear 
It  to  see  the 
itness  at  the 

the  media  of 

eous  humor, 
^ncied  resem- 

t  to  see  what 
arious  forms 
listinguished 
I  the  field  of 
lish. 

'rom  foreign 
enomeua. . 
ites  both  the 
ount  of  light, 
gins,  if  they 
pricked  in  a 
a  light  or  a 
(ther  eye  the 
may  be  seen 
second — i.  e., 
reased. 
eye  in  which 
tions  referred 
retina,  as  the 
,  416.  In  the 
lassive  (nega- 
from  objects 
ling  to  some 
it  those  from 
livergent,  are 
le  lens  is  rep- 
M  such  diver- 

lel  rays  cross 


VISION. 


676 


within  the  vitreous  humor,  and  diffusion-circles  being  formed 
on  the  retina,  the  image  of  the  object  is  necessarily  blurred, 


Pio  416.— Diain«in«  to  illustrate  conditions  of  refraction  In  normal  eye  when  unaooommo- 
dated  (passive,  or  negatively  accommodated),  and  when  accommodated  for  "near 
objects  (after  Landois). 

SO  that  an  object  must,  in  the  case  of  such  an  eye,  be  brought 
unusually  near,  in  order  to  be  seen  distinctly — i.  e.  the  near 


Fio.  417.  -Anomaliea  of  reftmotian  in  a  myopic  eye  (after  Landois). 

point  vi  abnormally  near  and  the  far  point  also,  for  parallel 
rays  can  not  be  focused ;  so  that  objects  must  be  near  enough 
for  the  rays  from  them  that  enter  the  eye  to  be  divergent. 

The  myopic  eye  is  usually  a  long  eye,  and,  though  the 
mechanism  of  accommodation  may  be  normal,  it  is  not  so 
usually,  the  ciliary  muscle  being  frequently  defective  in  some 
of  its  fibers,  which  may  be  either  hypertrophied  or  atrophied,  or 
with  some  affected  one  way  and  others  in  the  opposite.  More- 
over, there  is  also  generally,  in  bad  cases, "  spasm  of  accommo- 
dation" (i.  e.,  of  the  ciliary  muscle),  with  increased  ocular 
tension,  etc.  The  remedies  are,  rest  of  the  accommodation 
mechanism  and  the  use  of  concave  glasses. 


3.  The  opposite  defect  is  hypermetropia.  The  hypermetropic 


676 


ANIMAL  PHYSIOLOGY. 


eye  (Fig.  418),  being  too  short,  parallel  rays  are  focused  be- 
hind the  retina;  hence  no  distinct  image  of  distant  objects  can 


Fia.  4ia-AiMaiallM  of  nftMttoa  In  the  hypennMropio  qw  (aftar  Uuidato^ 

be  formed,  and  they  can  only  be  seen  clearly  by  the  use  of  con- 
vex glasses,  except  by  the  strongest  efforts  at  accommodation. 
When  the  eye  is  passive,  no  objects  are  seen  distinctly  beyond 
a  certain  distance — ^i.  e.,  the  near  point  is  abnormally  distant 
(eight  to  eighty  inches).  The  defect  is  to  be  remedied  by  the 
use  of  convex  glasses. 

4.  Presbyopia,  resulting  from  the  presbyopic  eye  of  the  old, 
is  owing  to  defective  focusing  power,  partly  from  diminished 
elasticity  (and  hence  flattening)  of  the  lens,  but  chiefly,  proba- 
bly, to  weakness  of  the  ciliary  muscle,  so  that  the  changes 
required  in  the  shape  of  the  lens,  that  near  objects  may  be  dis- 
tinctly seen,  can  not  be  made.  The  obvious  remedy  is  to  aid 
the  weakened  refractive  power  by  convex  glasses.  It  is  prac- 
tically important  to  bear  in  mind  that,  as  soon  as  any  of  these 
defects  in  refractive  power  (though  the  same  remark  applies 
to  all  ocular  abnormalities)  are  recognized,  the  remedy  should 
be  at  once  applied,  otherwise  complications  that  may  be  to  a 
large  extent  irremediable  may  ensue. 

YisnAL  Sbnsations. 

We  have  thus  far  considered  merely  what  takes  place  in  the 
eye  itself  or  the  physical  causes  of  vision,  without  reference  to 
those  nervous  changes  which  are  essential  to  the  perception  of 
an  object  It  is  true  that  an  image  of  the  object  is  formed  on 
the  retina,  but  it  would  be  a  very  crude  conception  of  nervous 
processes,  indeed,  to  assume  that  anything  resembling  that 
image  were  formed  on  the  cells  of  the  brain,  not  to  speak  of 
the  superposition  of  images  inconsistent  with  that  clear  mem- 
ory of  objects  we  retain.    Before  an  object  is  "  seen/'  not  only 


focused  be- 
i  objects  cau 


Uadols). 

e  use  of  con- 
ommodation. 
ttcfcly  beyond 
nally  distant 
odied  by  the 

'e  of  the  old, 
a  diminished 
diefly,  proba- 
the  changes 
B  may  be  dis- 
edy  is  to  aid 
,  It  is  prac- 
any  of  these 
mark  applies 
>medy  should 
may  be  to  a 


s  place  in  the 
;  reference  to 
perception  of 
is  formed  on 
»n  of  nervous 
ambling  that 
t  to  speak  of 
it  clear  mem- 
en/*  not  only 


VISION. 


677 


must  there  be  a  clear  image  formed  on  the  retina,  but  impulses 
generated  in  that  nerve  expansion  must  be  conducted  to  the 
brain,  and  rouse  in  certain  cells  there  peculiar  molecular  condi- 
tions, upon  which  the  perception  finally  depends. 

For  the  sake  of  clearness,  we  may  speak  of  the  changes 
effected  in  the  retina  as  sensory  impressions  or  impulses,  which, 
when  completed  by  corresponding  changes  in  the  brain,  develop 
into  sensations,  which  are  represented  psychically  by  percep- 
iions;  hence,  though  all  these  have  a  natural  connection,  they 
may  for  the  moment  be  considered  separately.  It  is  as  yet 
beyond  our  power  to  explain  how  they  are  related  to  each 
other  except  in  the  most  general  way,  and  the  manner  in 
which  a  mental  perception  grows  out  of  a  physical  alteration 
in  the  molecules  of  the  brain  is  at  present  entirely  beyond 
human  comprehension. 


•■•J 


■,^ 


FW.  «•. 


.  Fio. ' 


Fm: 


■  419.— Verttoal  ■Mtfcm  of  ntiii*  (after  H.  Kflller).    1.  lnjrer  of  rods  and  oobm  ;  I,  roda ; 

a,  eonw ;  4, 6,  e,  extoriMl  Knnnto  Ikrar ;  7,  intwiMl  grwiule  lajrer ;  »,  10,  fliiely  mmular 

grajr  kw«r ;  11,  lajrar  of  ncrveHMlls ;  It,  14,  flMn  of  <Ale  Mr«« ;  18.  membntM  Irniitena. 

.  m-OonnMUon  of  roda  fiid  oonea  of  r«tiiw  witfi  nerroiia  elemenu  <*fter  S^ppejr). 

TIm  nat  win  be  oleM' tram 


1,  a, a,  roda mmI  conea  aaan  fNm  in  (raot;  4, A, •, aida viaw. 
tm  preoedinK  figure. 

»7 


..^«;...»-^..--«jaMy.--.: 


578 


ANIMAL  PHYSIOLOGY. 


I  of  the  Eatiaa.— There  is  no  doubt  that  the  fibers  of 

the  optic  nerves  can  not  of  themselves  be  directly  affected  by 
light.  This  may  be  experimentally  demonstrated  to  one's  self 
by  a  variety  of  methods,  of  which  the  following  are  readily  car- 
ried out :  1.  Look  at  the  circle  (Fig.  421)  on  the  left  hand  with  the 


right  eye,  the  left  being  dosed,  and,  with  the  page  about  twelve 
to  fifteen  inches  distant,  gradually  approximate  it  to  the  eye, 
when  suddenly  the  cross  will  disappear,  its  image  at  that  dis- 
tance having  fallen  on  the  bUndspot,  or  the  point  of  entrance 
of  the  optic  nerve.  2.  Fixing  the  eye  as  before  on  a  mark  on 
a  sheet  of  white  paper  made  by  a  pen,  draw  the  latter  outward 
till  its  point  disi^ypears  from  view.  Mark  the  location  of  the 
pen-point  when  this  occurs,  and  continue  the  movement  till  it 
again  appears.  Mark  this  point  also.  This  process  may  be 
continued  in  other  directions  bendes  the  horizontal,  and,  by 
joining  these  pcnmts,  an  irr^nilar  outline  is  formed,  marking 
off  a  portion  of  the  "  visual  field,"  within  which  there  is  really 
no  vision.  8.  A  small  image  from  a  fbune  projected  on  the 
blind-spot  by  a  mirror  is  not  visible*  though  readily  perceived 
when  it  falls  OD.  the  retina  proper. 


«S  dMMrold; 


g,g,  moleeutar  korw 


i^oifaaaf  mae^MM(«flarH«iliV).   •.  a,  viOHat  or  dmraid 

1  ji;tss?«s!:5&r«%iss'oy^^      "^ 


It  remains,  then,  to  determine  what  part  of  the  retina  is 
affected  by  light.    The  evidence  that  it  is  the  layers  of  rods 


IWi»lilMIM.'IW»'«»-'.JJJ'---ll*MMI^.UvtJWWW»l?.t'il^llltWI'IIW^ 


he  fibers  of 
affected  by 
o  one's  self 
readily  car- 
ad  with  the 


VISION. 


S79 


,boiit  twelve 
I  to  the  eye, 
at  that  dis- 
of  entrance 
1  a  mark  on 
iter  outward 
ation  of  the 
ement  till  it 
iess  may  be 
tal,  and,  by 
,ed,  marking 
lere  is  really 
icted  on  the 
ly  peroeiTed 


. at  dMNToM; 

ir  iraaalar  lajrer; 

the  retina  is 
kyers  of  rods 


and  con  s  is  convincing.  If  it  could  be  shown  that  parts  of 
the  retina  itself  internal  to  these  layers  cast  perceptible  shad- 
ows, the  conclusion  that  the  rods  and  cones  are  the  essential 
parts  of  the  sensory  organ  would  be  inevitable.  The  following 
experiment  proves  this :  When  a  light  is  moved  backward  and 
forward  (to  prevent  retinal  fatigue)  before  the  eye,  so  that  the 
rays  from  it  enter  the  organ,  while  the  subject,  standing  in  a 
dark  room,  gazes  toward  a  plain-colored  wall,  his  accommoda- 
tion being  relaxed,  he  will  behold  radiating  shadows,  somewhat 
suggestive  of  the  leafless  branches  of  an  old  tree.  These  cor- 
respond with  the  picture  of  the  retinal  vessels  as  ascertained 
by  an  examination  of  the  eye  with  the  ophthalmoscope.  Some 
persons  always  see  the  shadows  of  the  blood-corpuscles  also ; 
and,  in  fact,  one  physiologist  has,  by  observing  these,  calculated 
the  rate  of  the  blood-flow  in  the  retinal  vessels.    Instead  of 


region 


rio.  4M. 


E-r_  ^.^_'_.^-^  the  pota*  of  catnnoeoC^^iiiie  nerre,  In  Um 

tekl 
lUwi 
icli,b 
Tnui 

Ctftt 

into  Om  vJMMl  fltrid  i^  d-JOf  morinK  the  < 


In  HmmS.  OP  nticli  [■■■^■lio  ittiHiMpiMiiiil 
region  <x  which  the  pRMninentvcinb  may  1 


be  Men  to  nriee  (nfter 


In  thii  ceae  the  Ufcht 


ttMrellMa 

its  Image  win  he  tWrmed  «t 


at  wt^point  iiuidowe  a|i|iear,and  are 
(T,  !••  gat  new  relative  poal- 


^M  reAeeted  toi 
_.Jdatd.   BgrmoTiai 
ete.  (after  Beniatein). 

moving  the  light  to  and  fro,  it  may  be  concentrated  for  a  few 
seconds  by  a  lens  with  the  same  result— the  appearance  of 
Pwrkifkje's  figures,  as  they  are  termed.  When  the  light  is 
moved,  they  shift  place  correspondingly.  If  the  sensory  parts 
were  not  situated  behind  the  retinal  vessels,  it  is  impossible  to 
conceive  how  their  shadows  coixld  be  seen,  and  certain  mathe- 


KBMMH 


680 


ANIMAL  PHYSIOLOGY. 


matical  calculations,  based  on  data  derived  from  'the  experi- 
ment just  described,  locate  the  pari;  concerned  in  the  layer  of 
rods  and  cones.  Putting  together  all  the  facts  of  experiment 
with  those  derived  from  pathological  conditions,  there  seems 
to  be  no  reasonable  doubt  that  the  rods  and  cones  of  the  retina 
are  the  seat  of  origin  of  the  visual  impulses. 

The  performance  of  the  experiment  as  given  above  requires 
usually  two  persons,  but  there  are  simpler  methods,  which,  in 
some  cases,  also  bring  out  the  figures  more  satisfactorily:  (1) 
It  often  suffices  to  move  the  head  back  and  forward  before  the 
tube  of  a  microscope  without  its  objective ;  or  (2)  to  move  rapidly 
a  card  with  a  pin-hole  held  close  before  the  eye,  while  the  sub- 
ject gazes  at  a  bright  clear  sky.  When  the  card  is  moved  from 
side  to  side,  the  vertical  vessels  are  seen ;  if  ^p  and  down,  the 
horizontal.  The  shadows  of  the  capillaries  come  out  especially 
well  by  this  method.  It  is  essential,  however,  whatever  plan 
be  adopted,  to  gaze  into  infinite  distance,  as  it  were,  in  order 
fully  to  relax  the  accommodation  and  to  avoid  excessive  ex- 
pectancy, which  frustrates  the  former  attempts  at  relaxation. 

Th«  Vaton  of  the  ProesiMs  mkUk  Mrigiaato  Yiwul  LftpidsM.— 
Much  interest  attached  at  one  time  to  visual  purple  (rhodop- 
sin),  because  it  was  hoped  that  it  might  furnish  a  chemical  ex- 
planation of  vision.  It  was  found  that  in  certain  animals,  as 
frogs,  when  kept  in  darkness,  the  visual  purple  was  renewed 
after  having  been  bleached  out  by  exposure  to  light ;  indeed  an 
exact  **  optogram,"  or  picture  of  an  object,  might  be  made  and 
by  appropriate  reagents  fixed  on  the  retina  as  a  bleached  part 
of  the  visual  purple. 

This  substance  is  found  exclusively  in  the  outer  limbs  of  the 
rods  and  not  at  all  in  the  cones ;  but,  since  the  retinas  of  some 
animals  (snakes)  are  destitute  of  rods,  and  visual  purple  is  also 
wanting  in  the  macula  lutea  and  fovea  centralis  of  man  and 
the  apes,  the  points  of  greatest  retinal  sensibility,  it  is  manifest 
that  the  theory  based  upon  its  presence  breaks  down  as  an  ex- 
planation of  vision,  if  to  be  applied  universally^;  besides,  the 
retinas  of  some  animals  with  rods  (dove,  hen,  bat)  are  entirely 
devoid  of  visual  purple. 

But,  though  this  particular  method  of  application  of  chem- 
istry to  the  explanation  of  the  origin  of  retinal  impulses  has 
failed,  it  does  not  follow  that  a  chemical  theory  as  such  is  false, 
though  it  must  be  admitted  that  the  evidence  is  as  yet  very 
incomplete  on  which  to  found  such  an  explanation. 

But  when  we  consider  the  evolution  of  the  eye,  and  examine 


lummi  iiiii^jjtwiMMawMWWgHwawwgwaiMwiM^^ 


'the  experi- 
the  layer  of 
experiment 
there  seems 
>f  the  retina 

ove  requires 
Is,  which,  in 
Actorily:  (1) 
1  before  the 
nove  rapidly 
idle  the  sub- 
moved  from 
id  down,  the 
at  especially 
latever  plan 
9re,  in  order 
ixcessive  ex- 
relaxation. 
1  LapoliM.— 
'pte  (rhodop- 
chemioal  ex- 
1  animals,  as 
was  renewed 
t ;  indeed  an 
be  made  and 
leached  part 

limbs  of  the 
Lnas  of  some 
)urple  is  also 
I  of  man  and 
It  is  manifest 
>wn  as  an  ex- 
;  besides,  the 
I  are  entirely 

ion  of  chem- 

impulses  has 

such  is  false, 

s  as  yet  very 

1. 

and  examine 


VISION. 


681 


msmiMsiUi 


into  the  facts  of  comparative  anatomy  and  physiology,  there 
are  many  of  a  significance  that  we  can  not  ignore ;  the  impor- 
tance of  light  to  most  protoplasmic  processes,  such  as  the  ac- 
cumulation of  pigment  in  certain  regions  marking  the  very 
beginnings  of  eyes ;  the  large  amoimt  of  pigment  found  in  the 
eyes  of  most  groups  of  animals  and  of  nearly  all  mammals  sug- 
gesting that  this  is  a  provision  for  the  retention  of  light,  which 
we  can  scarcely  conceive  as  acting  in  other  than  a  chemical 
manner.  At  the  same  time,  in  keeping  with  the  spirit  of  this 
work  throughout,  we  suggest  caution  in  believing  that  explana- 
tions based  on  our  limited  experience  are  the  only  ones  possible. 
^  It  is  worth  while  to  bear  in  mind,  however,  that  currents  of 
rest  and  currents  of  action  similar  to  those  demonstrated  to 
exist  in  muscle,  glands,  nerves,  etc.,  may  be  shown  to  exist  in 
the  retina.  In  all  the  other  cases  these  are  in  intensity  parallel 
to  the  degree  of  functional  (and  chemical)  activity  of  the  part, 
and  it  makes  the  probability  of  there  being  a  chemistry  of  the 
retina  as  a  foundation  for  the  impulses  therein  generated  great- 
er. The  subject  is  as  yet,  however,  in  the  region  rather  of 
speculation  than  of  ascertained  fact. 

TIm  iMVi  of  Batiaal  ttimidation.— It  may  be  noticed  that,  when 
a  circular  saw  in  a  mill  is  rotated  with  extreme  rapidity,  it  seems 
to  be  at  rest. 

If  a  stick  on  fire  at  one  end  be  rapidly  moved  about,  there 
seems  to  be  a  continuous  fiery  circle. 

If  a  top  painted  in  sections  with  various  colors  be  spun,  the 
different  colors  can  not  be  distinguished,  but  there  ia  a  color 
resulting  from,  the  bloiding  of  the  sensations  from  tiiem  all, 
which  will  be  white  if  the  spectral  colors  be  employed. 

When,  on  a  dark  night,  a  moving  animal  is  illuminated  by 
a  flash  of  lightning,  it  seemB  to  be  at  rest,  though  the  attitude 
is  one  we  know  to  be  appropriate  for  it  during  locomotion. 

It  becomes  necessary  to  explain  these  and  similar  phe- 
nomena. Another  observation  or  two  will  furnish  the  data  for 
the  solution. 

If  on  awakening  in  the  morning,  when  the  eyes  have  been 
well  rested  and  the  retina  is  therefore  not  so  readily  fatigued, 
one  looks  at  the  window  for  a  few  seconds  and  then  closes  the 
eyes,  he  may  xierceive  that  the  picture  still  remains  visible  as 
a  ppaitive  after-^mcige  ;  while,  if  a  light  be  gazed  upon  at  night 
and  the  eyes  suddenly  closed,  an  after-image  of  the  light  may 
be  observed. 

It  thus  appears,  then,  that  the  impression  or  sensation  out- 


^^ipaplUlilBa^Bi. 


ANIMAIi  PHYSIOLOOT. 


iMts  the  stimulus  in  tl^ese  cases,  and  this  is  the  explanation 
into  which  all  the  above-mentioned  facts  fit.  When  the  fiery 
point  passing  before  the  eyes  in  the  case  of  the  fire-brand  stimu- 
lates the  same  parts  of  the  retina  more  frequently  than  is  con- 
sistent with  the  time  required  for  the  previous  impression  to 
fade,  there  is,  of  necessity,  a  continuous  sensation,  which  is  in- 
terpreted by  the  Qiind  as  referable  to  one  object.  In  like  man- 
ner, in  the  case  of  a  moving  object  seen  by  an  electric  flash,  the 
duration  of  the  latter  is  so  brief  that  the  object  illuminated  can 
not  make  any  appreciable  change  of  position  while  it  lasts ;  a 
second  flash  would  show  an  alteration,  another  part  of  the  retina 
being  stimulated,  or  the  original  impression  having  faded,  etdi 

In  the  case  of  a  top  or  (better  seen)  color-disk,  painted  into 
black  and  white  sectors,  it  may  be  observed  that  with  a  faint 
light  the  different  colors  cease  to  appear  distinct  with  a  slower 
rotation  than  when  a  bright  light  is  used.  The  variation  is 
between  about  ^  and  ^  of  a  second,  according  to  the  intensity 
of  the  light  used.  Fusion  is  also  readier  with  some  colors  than 
others. 

It  is  a  remarkable  fact  that  one  can  distinguish  as  readily 
between  the  quantity  of  light  emanating  from  10  and  11  can- 
dles as  between  100  and  110.  Weber's  law  is  a  highly  general- 
ized toriu  of  this  statement  pnplicable  to  all  the  senses. 

But  with  vision,  as  with  a11  the  senses,  a  lower  and  espe- 
cially an  upper  limit  is  soon  reached,  within  which  alone  we 
can  discriminate.  It  in  not  possible  to  distinguish  between  the 
difference  in  brightness  of  the  central  and  the  circumferential 
parts  of  the  sun,  though  it  is  known  that  the  actual  difference 
is  very  great,  while  it  is  easy  enough  to  recognize  a  marldd 
difference  in  the  light  of  a  room  when  two  candles  are  used  in- 
stead of  one.  Within  certain  limits  we  can  appreciate  a  differ- 
ence in  illuminating  power  of  about  j^  of  a  given  total 

Th«  Yiraul  Aafl*.— If  two  points  be  marked  out  with  ink  on 
a  sheet  of  white  paper,  so  close  together  that  they  can  be  just 
distinguished  as  two  at  the  distance  of  12  to  20  inches,  then  on 
removing  them  a  little  farther  away  they  seem  to  merge  into 
one. 

The  principle  involved  may  be  stated  thus :  When  the  dis- 
timce  between  two  points  is  such  that  they  subtend  a  less  visual 
angle  than  60  seconds,  they  cease  to  be  distinguished  as  two. 
Fig.  426  illustrates  the  visual  angle.  It  will  be  noticed  that  a 
largierol^t  at  a  greater  diistance  subtends  the  same  visual 
angle  •■  a  mudler  one  much  nearer.    The  size  of  the  retinal 


iffia 


mmm 


li^&SdCB^SKiM 


explanation 
en  the  fiery 
)rand  stimu- 
bhan  is  con- 
apression  to 
which  is  in- 
[n  like  man- 
ric  flash,  the 
iminated  can 
e  it  lasts;  a 
of  the  retina 
g  faded,  et(^ 
painted  into 
with  a  faint 
ith  a  slower 
variation  is 
the  intensity 
e  colors  than 

sh  as  readily 
)  and  11  can- 
i^hly  general- 
tnses. 

'BT  and  espe- 
ich  alone  we 
between  the 
rcumferential 
iial  difference 
ize  a  marl.ed 
s  are  used  in- 
ciate  a  diff er- 
1  totaL 

t  with  ink  on 
)y  caxk.  be  just 
iches,  then  on 
to  merg^  into 

iVhen  the  dis- 
i  a  less  visual 
ished  as  two. 
.oticed  that  a 
)  same  visual 
at  the  retinal 


VISION. 


588 


image  corresponding  to  60  seconds  is  '004  mm.  (4  /i),  and  this 
is  about  the  diameter  of  a  single  rod  or  cone.    It  is  not,  how- 


ris.  4».-TheTteMlMia:le.  TlMobjMit«t^"«iiiWM«iM>lM«ertlMntlwone»til(Le.Ooiite). 

ever,  true  that  when  two  cones  are  stimulated  two  objects  are 
inferred  to  exist  in  every  case  by  the  mind ;  for  the  retina 
varies  in  different  parts  very  greatly  in  general  sensibility  and 
in  sensibility  to  color. 

It  is  noticeable  that  visual  discriminative  power  can  be 
greatly  improved  by  culture,  a  remark  which  applies  especially 
to  colors.  It  seems  altogether  probable  that  the  change  is  cen- 
tral in  the  nerve-cells  of  the  part  or  parts  of  the  brain  con- 
cerned, especially  of  the  cortical  region,  where  the  cell  processes 
involved  in  vision  are  finally  completed. 

0glor4«aiilifliuk— As  this  subject  is  still  in  a  very  unsettled 
condition,  it  will  be  well  in  discussing  it  to  keep  the  facts  of 
physiology  and  of  physics  distinct  from  each  other  and  from  the 
theories  proposed  to  account  for  them. 

It  is  rare  to  see  in  nature  the  pure  colors  of  the  spectrum ; 
more  frequently  the  reds,  blues,  etc.,  we  behold  are  the  corre- 
sponding colors  of  the  spectrum,  with  the  addition  of  a  variable 
quantity  of  white  light.  In  the  spectrum  itself  there  is  an 
unlimited  number  of  shades,  not  usually  specially  noticed,  in- 
termediate between  the  main  colors. 

Hence  we  may  regard  a  color  as  dependent  on  (1)  the  wave- 
length of  its  constituent  rays;  (8)  on  the  quantity  of  the  par- 
ticular light  falling  on  the  retina;  and  (3)  on  the  quantity  of 
white  light  mixed  with  this.  When  no  white  light  at  all  enters, 
the  color  is  said  to  be  saturated,  such  being  heavy  and  eestheti- 
cally  unattractive;  when  much  of  such  light,  bright, etc.  A 
gray  results  from  a  certain  mixture  of  white  with  black ;  the 
browns  by  fusion  of  red,  yellow,  white,  and  black.  But  in  this 
and  all  other  instances  in  which  we  speak  of  "  fusion,"  "  blend- 
ing," "mixture,"  etc.,  we  refer  to  physiological  blending  owing 
to  contemporaneous  stimulation  by  light  of  different  wave- 
lengths. Thus,  orange  results  from  the  action  of  the  red  and 
fellow  rays  at  the  same  time,  and  can  not  be  produced  by  any 


53g3B»!S>83S«SSi! 


■■'^f^^^^*  1— >»,■»■  ^**^''^-^'^j|ij^^^|^^_J|tj^^ 


ANIMAL  PHYSIOLOGY. 

mixture  of  the  wave-lengths  of  red  and  yellow.  Again,  certain 
colors  known  as  complementary  by  psychic  fusion  gave  rise 
to  white,  though  no  physical  mixture  of  such  colored  pig- 
ments will  produce  white.  These  are  red  and  blue-green; 
orange  and  blue;  yellow  and  indigo-blue;  green-yellow  and 
violet. 

Now,  when  a  child  beholds  orange,  he  has  not  the  faintest 
idea  that  it  is  related  to  red,  or  that  white  can  be  in  any  way 
produced  from  any  combination  of  colors,  any  more  than,  when 
he  hears  a  perfect  musical  chord,  has  he  any  idea  of  its  being 
produced  by  the  simultaneous  production  of  its  component 
notes.  To  him  both  the  colors  and  the  chord  are  independent 
facts.  But  by  simple  experiments  their  origin  may  be  illus- 
trated. As  regards  comple- 
mentary colors,  Lambert's  ex- 
periment may  easily  be  per- 
formed: Place  a  red  wafer  (or 
a  slip  of  paper)  on  a  sheet  of 
white  paper,  and  about  three 
inches  behind  it  a  blue  one. 
Hold  a  plate  of  glass  be- 
tween the  two  and  vertically, 
so  that  while  gazing  at  the 
red  wafer  through  it  a  re- 
jected image  of  the  blue  one 
will  be  thrown  into  the  eye  in  the  same  direction  as  that  of  the 
red  image,  the  result  being  a  sensation  of  purple. 

As  before  referred  to,  a  rotating  disk  on  which  all  the  colors 
of  the  spectrum  are  represented  in  equal  subdivisions,  when  the 
speed  is  sufficiently  great,  appears  white  from  the  fusion  of  the 
sensations.  Of  course,  instead  of  all  the  colors,  complementary 
ones  suffice.  As  a  matter  oflBBt,  we  may  recognize  six  funda- 
mental oolowK-white,  black,  red,  yellow,  green,  and  blue— and 
these  may  be  ^outcome  of  the  physiological  mixture  of  three 
"  standard  "  sensations. 

"We  now  proceed  to  matters  of  speculation.  At  the  present 
day  two  theories  to  account  for  color-vision  monopolize  atten- 
tion :  1.  The  Young-Eelmholtz  theory  assumes  that  there  are 
only  three  primary  sensations,  or,  in  other  words,  that  the  reti- 
na is  affected  only  by  rays  of  light  corresponding  to  red,  green, 
and  violet  (or  blue) ;  and  the  manner  in  which  any  color  is  pro- 
duced (iA  the  mind)  "will  app^r  from  an  examination  of  Fig. 
487.     Thus,  when  red  is  the  color  seen,  though  the  retinal 


;! 

K 

/ 

\ 

\ 

T"  ■ 

(         f 

TlMmtea 


'   -      ptateataQiftarBMnMMii). 


mmimmmmmsmKimm 


ain,  certain 
1  gave  rise 
solored  pig- 
blue-green  ; 
yellow  and 

the  faintest 
in  any  way 

than,  when 
of  its  being 

component 
ndependent 
ay  be  illus- 
>ds  comple- 
uubert's  ex- 
sily  be  per- 
ad  wafer  (or 
1  a  sheet  of 
about  three 
%  blue  one. 
:  glass  be- 
4  vertically, 
zing  at  the 
^h  it  a  re- 
tie  blue  one 
i  that  of  the 

,11  the  colors 
08,  when  the 
'usion  of  the 
iplementary 
e  six  f  unda- 
i  blue— and 
lUte  of  three 

;  the  present 
polize  atten> 
at  there  are 
hat  the  reti- 
0  red,  green, 
color  is  pro- 
ition  of  Fig. 
the  retinal 


VISION. 


686 


stimulation  is  not  confined  solely  to  the  rays  of  the  red  end  of 
the  spectrum,.it  is  chiefly  by  these  that  what  we  may  call  psy- 
chic red  is  produced — i.  e.,  the  mental  perception  of  red  is  de- 
pendent on  a  specific  stimulation  of  the  retina  by  rays  of  a  cer- 
tain wave-length,  though  at  the  same  time  there  is  a  feebler 
sensation  of  green  and  violet.    Orange  would  in  like  manner 


ii^^W^ 


Fio.  487.— niiMtntM  the  YouiiK-HelinhoIta- theory  of  c(rfor-vliioB.  The  lelton  in  the  lower 
line  indickte  oolon  of  qpeSum  in  natural  order,  l.denotca  the  "red";  8,  "green";  S, 
"violet"  primary-color  wneation.  The  diagram  ahowa  hy  the  height  of  the  curve  in 
each  instance  to  what  extent  the  ptlmarr-oolor  aenaatlona  are  reqwcthreljr  excited  bf 
vttirationa  of  diSWent  waTe-lengUia  (after  Benwtein). 

result  from  a  large  admixture  of  red,  considerable  of  green,  and 
very  little  of  violet.  2.  Bering's  theory  is  a  chemical  one.  He 
assumes  the  existence  of  three  kinds  of  visual  substances: 
white-black,  yellow-blue,  red-green.  Either  in  the  retina  or 
elsewhere  in  the  eye  it  is  believed  that  two  processes  are  in  con- 
stant operation,  the  opposite  of  each  other,  and  which  corre- 
spond to  the  changes  assumed  to  take  place  in  protoplasm 
generally,  and  to  which  we  have  referred  already  as  ana- 
bolism  and  katabolism,  or  construction  (assimilation)  and  de- 
struction (dissimilation).  When  dissimilation  is  in  excess,  the 
lighter  colors  result — ^white,  yellow,  red ;  and  the  others  when 
assimilation  prevails  Orange  would  be  seen  whep  red  and 
■  yellow  are  simultaneously  produced — ^i.  e.,  when  the  red-green 
and  yellow-blue  substances  both  undergo  dissimilation  to  a 
degree  in  excess  of  its  opposite  phase. 

One  test  of  these  theories  would  be  their  application  to  ex- 
plain the  defect  next  to  be  mentioned. 

Oolor'BUndiMM.— There  are  all  degrees  of  this  defect,  from' 
such  as  exists  in  every  eye — i.  e.,  inability  to  perceive  color 
equally  well  by  all  parts  of  the  retina,  to  complete  loss  of  the 
faculty  of  discriminating  color  at  all. 

1.  Complete  coior-Jbilindnesa  (achromatopsy)  is  marked  by 
inability  to  distinguish  any  colors,  the  spectrum  being  brightest 


5$6 


ANIMAL  PHYSIOLOGY. 


in  the  middle,  but  any  picture  appears  as  a  photograph.    It 
may  be  unilateral. 

2.  Yellow-Bit^  Blindneaif.— The  spectrum  presents  only  red 
and  green,  and  hence  is  usually  much  shortened.  It  is  occa- 
sionally unilateral. 

3.  Red-Qreen  Mindnesa  (Daltonism).— Yellow  and  blue  may 
be  discriminated,  violet  and  blue  seem  alike,  and  red  and  green 
practically  do  not  exist. 

It  is  to  be  borne  in  mind  that  it  is  very  difficult  to  ascer- 
tain the  exact  condition  of  color-blind  persons,  from  their  in- 
ability to  communicate  their  state  of  mind.  They  often  make 
discriminations  apparently  based  on  color  distinctions,  but,  in 
reality,  on  the  form,  texture,  position,  etc.,  of  objects.  It  is 
also  all  but  impossible  to  be  precisely  certain  as  to  the  extent 
to  which  the  lower  animals  can  distinguish  between  colors. 

To  apply  the  above  theories  of  color-vision  to  the  explana- 
tion of  color-blindness :  In  the  case  of  red-green  blindness,  ac- 
cording to  the  Young-Helmholtz  explanation,  there  is  the  ab- 
sence of  one  of  the  primary  sensations  (red),  so  that  the  colors 
seen  are  the  result  of  mixtures  of  the  other  two  primary  sensa- 
tions. What  we  call  yellow  must  be  to  the  subject  of  this 
defect  a  bright  green.  According  to  Hering's  theory  such 
persons  lack  the  red-green  substance ;  hence  their  color- vision 
must  be  limited  to  mixtures  of  yellow  and  blue  alone.  But,  if 
blindness  to  red  and  green  can  exist  separately,  as  has  been  as- 
serted, this  theory  fails  to  explain  it,  though  the  former  would ; 
while  total  color-blindness  is  explicable  by  Hering's  theory, 
but  not  by  the  rival  one.  It  is  probable  that  neither  is  broad 
enough  to  meet  the  facts,  even  if  correct  in  principle.  They 
serve  the  end  of  being  provisional  hypotheses  till  better  are 
found. 

.    Psychological  Aspects  of  Vision. 

It  is  impossible  to  ignore  entirely,  in  treating  of  the  physi- 
ology of  the  senses,  the  mind,  or  perceiving  ego. 

By  virtue  of  our  mental  constitution,  we  refer  what  we 
"  see  "  to  the  external  world,  though  it  is  plain  that  all  that  we 
'  perceive  is  made  up  of  certain  sensations. 

We  recognize  the  "visual  field"  as  that  part  of  the  outer 
world  within  which  alone  our  vision  can  act  at  any  one  time ; 
and  this  is,  of  course,  smaller  for  one  than  for  both  eyes. 

If  one  takes  a  large  sheet  of  paper  and  marks  on  its  center 
a  spot  on  which  one  or  both  eyes  are  fixed,  by  moving  a  point 


.  atss.  xiKssaSes^es^^ 


VISION. 


687 


>graph.    It 

ts  only  red 
It  is  occa- 

d  blue  may 
i  and  green 

t  to  ascer- 
n  their  in- 
of  ten  make 
ons,  but,  in 
ects.    It  is 

the  extent 
colors, 
le  explana- 
indness,  ac- 
I  is  theab- 
)  the  colors 
nary  sensa- 
ect  of  this 
lieory  such 
;olor-vision 
ae.  But,  if 
Las  been  as- 
tner  would ; 
g's  theory, 
ler  is  broad 
iple.    They 

better  are 


the  physi- 

r  what  we 
all  that  we 

{  the  outer 
J  one  time ; 
eyes. 

a  its  center 
ing  a  point 


up  or  down,  to  the  right  or  the  left,  he  may  ascertain  the  limits 
of  the  visual  field  for  a  plane  surface.  The  visual  field  for 
both  eyes  measures  about  180°  in  the  horizontal  meridian;  for 
one  eye  about  145° ;  and  in  the  vertical  meridian  100°. 

Lapcrfcotioiis  of  Vinul  PuDoepUanii — We  may  now  consider 
some  defects  which  we  know  to  exist  by  the  use  of  our  reason- 
ing powers  in  the  mental  perception  we  form  of  objects  in  the 
visual  field : 

1.  Irradiation. — It  is  easy  to  notice  that  a  white  spot  on  a 
dark  ground  appears  larger  than  a  dark  spot  of  equal  size  on 
a  white  ground.     This  has  been  spoken  of  as  the  result  of 


Fio.  «M.— nhMtntw  imkUatiim.   The  iriiito  patch  in  the  (bwfc  (tround  i 
dark  one  tai  the  light  grauiid  (after  Bematetn). 


I  langer  than  the 


irradiation— a  sort  of  overflow  of  sensation,  though  whether 
to  be  referred  to  the  retina  or  to  the  brain-areas  concerned  is 
uncertain. 

2.  Contrast. — When  a  white  strip  of  paper  is  laid  between 
two  black  ones,  the  center  of  the  white  strip  is  not  so  bright  as 
its  edges,  from  contrast ;  and  experiments  illustrating  the  same 
principle  may  be  made  with  colored  paper.  This  law  of  con- 
trast is  very  wide  in  its  application,  and  will  be  referred  to 
later.  -  , 

3.  The  Mimd-Spot. — It  might  be  supposed  at  first  that  one 
should  perceive  gaps  in  the  field  of  vision  on  account  of  the 
blind-spot;  biit,  when  it  is  remembered  that  to  see  black  we 
must  have  a  definito  sensation,  and  that  the  nrind  places  objects 
Ijring  on  opposite  sides  of  the  spot  close  together,  the  reason 
that  this  defect  in  structure,  if  such  it  really  be,  is  practically 
inoperative,  becomes  clearer.  It  is  to  be  remembered  that  the 
image  of  an  object  (see  Fig.  432)  never  falls  on  the  blind-spot 
in  both  eyes;  and,  moreover,  this  area  lies  outside  of  that 
of  greatest  acuteness  {macula  Itiiea),  on  which  images  are 
focused. 

The  macula  lutea,  and  especially  the  fovea  centralis,  are  the 


^-■"^iumtmms/tsiiii^iM'^i^ 


«i»«B3eiiaMwBiititaiiwafe<a^^ 


688 


ANIMAL  PHYSIOLOGY. 


parts  of  the  retina  most  sensitive  to  both  form  and  color ;  or, 
to  put  it  otherwise,  when  the  retina  is  stimulated  by  an  object, 
whether  colored  or  not,  the  mind  perceives,  becomes  most  read- 
ily cognizant  of  the  sensation,  sees  the  object  best,  when  the 
stimulation  is  confined  to  the  yellow  spot;  and,  as  will  be 
learned  still  more  fully  later,  all  the  arrangements  for  vision 
are  directed  toward  the  focusing  of  the  rays  of  light  that 
emanate  from  objects,  so  that  the  image  may  fall  on  this  region 
of  the  retina. 

In  like  manner,  by  looking  directly  forward,  and  having 
some  one  move  an  object  in  space  as  before,  and  noting  when 
it  ceases  to  be  visible,  an  irregular  figure  of  the  field,  within 
which  vision  is  distinct  in  varying  degrees,  and  beyond  which 
it  is  absolutely  non-existent,  may  be  mapped  out. 

By  using  colored  objects,  as  small  squares  of  paper,  by  the 
above  method,  it  may  be  readily  learned  that  the  field  for  some 
colors  is  much  more  restricted  than  for  others;  in  fact,  as  such 
an  object  is  moved  outward,  its  color  seems  to  change:  thus, 
purple  becomes  bluish.  Jn  all  retinas  there  is  more  or  less 
color-blindness  toward  the  peripheral  parts,  and  this  is  espe- 
cially true  of  red.  The  field  for  the  colors  of  the  spectrum,  etc., 
may  easily  be  shown  to  be  more  limited  than  for  white. 


■■S" 


'**J*;:2S*^*ft^'*H*j'  rteht we, ••  pwjwsled  bj tlw  Mbject on tlw inner 
'*'  %''?'!!5l?>SSl^P>'*'^7>^^'<*™*>>»  point  of  SntioB  (ortte  ere :  MmiHl 
mMe  (after  SMttahTp  endLMidolt).  T,  temponl  iide ;  M ,  nMia  ride ;  w.  ImniM 
while ;  ■,  for bhw ;  B, lorred ;  a,  for giwn. 


rmrlkoe 

■eniiHliagrain- 

~,  tMMindMT  for 


VISION. 


589 


id  color;  or, 
\}y  an  object, 
NS  most  read- 
Bt,  when  the 
,  as  will  be 
ts  for  vision 
f  light  that 
a  this  region 

and  having 
noting  when 
field,  within 
Byond  which 

Miper,  by  the 
ield  for  some 
fact,  as  such 
bange:  thus, 
more  or  less 
this  is  espe- 
>ectrum>  etc., 
rhite. 


I  the  inner  Mirteo* 
re:  lemi-diagraiB- 
;  w.  boundaiT  for 


Influence  of  the  Pigment  of  the  Macvla  Lutea.— If  we  inter- 
pose a  solution  of  chrome  alum  between  the  eye  and  a  white 
cloud  while  the  general  field  is  purplish,  a  rosy  patch  appears 
in  a  position  corresponding  to  the  yellow  spot.  This  is  owing 
to  the  fact  that  the  solution  allows  only  the  red  and  greenish- 
blue  rays  to  pass,  and,  the  latter  being  absorbed  by  the  yellow 
spot,  we  see  only  the  former  in  the  part  of  the  field  of  vision 
corresponding  to  this  area.  The  experiment  is  also  an  excellent 
one  to  mark  out  the  site  of  the  spot.  Since  the  macula  lutea 
is  the  part  of  the  retina  concerned  in  the  usual  so-called  "  di- 
rect" vision,  it  will  be  evident  that  what  would  be  yellow  »but 
for  the  influence  of  the  pigment  of  this  spot  appears  to  us 
white. 

Afl«r>ImafH  *te> — Positive  after-images  have  already  been 
referred  to;  but  an  entirely  different  result,  owing  to  exhaus- 
tion of  the  retina,  may  follow  when  the  eye  is  turned  from  the 
object.  If,  after  gazing  some  seconds  at  the  sun,  one  turns  away 
or  merely  closes  the  eyes,  he  may  see  black  sunq:  In  like  man- 
ner, when  one  turns  to  a  gray  surface  after  keeping  the  eyes 
fixed  on  a  black  spot  on  a  white  ground,  he  will  see  a  light  spot. 
Such  are  termed  negative  after-images,  and  these  may  them- 
selves be  colored,  as  when  one  turns  from  a  red  to  a  white  sur- 
face and  sees  the  latter  green.  They  may  be  explained  upon 
either  theory  of  color-vision.  According  to  the  theory  of 
Toung  and  Helmholtz,  in  the  latter  case  the  green  appears  be- 
cause the  primary  color-sensation  for  red  is  exhausted,  while 
the  others  become  more  prominent  accordingly ;  but  it  is  more 
difficult  to  explain  the  black  suns,  etc.,  by  this  theory,  though 
it  is,  of  course,  open  to  suppose  that  all  the  primary  color-sen- 
sations have  been  exhausted. 

According  to  Hering's  theory,  the  dark  after-images  as  well 
as  the  colored  ones  are  the  result  of  the  preponderance  of  one 
or  the  other  of  the  two  processes  of  assimilation  and  dissimila- 
tion. But,  in  truth,  the  subject  is  very  difficult  of  complete 
solution  at  all  by  the  kind  of  explanations  we  are  at  present 
employing. 

It  is  of  some  importance  to  remember  that  the  retina  is  not 
equally  sensitive  to  all  colors.  We  see  the  blues  of  evening 
more  readily  than  the  reds  or  yellows,  hence  the  employment 
of  the  former  extensively  by  artists  in  depicting  evening 
scenes. 

Since  there  is  a  maximum  point  of  stimulation  for  each  main 
color,  it  is  possible  to  understand  how,  by  increase  of  the  inten- 


4\ 


«i4ra,?!.";iSrSS>W»iSSWSrr«SWI»KE«IS?K3J^^ 


J 


590 


ANIMAL  PHYSIOLOGY. 


sity  of  its  light,  one  color  passes  into  another:  e.  g.,  let  violet 
light  be  gradually  increased  in  intensity,  and  the  retina  soon 
fails  to  perceive  this  cqlor  so  strongly ;  but  the  red  and  green 
sensations  being  as  yet  submaximal,  we  perceive  a  color  the 
result  of  the  blending  of  these  two  with  violet,  and  so  on  till 
we  may  get  such  a  mixture  of  the  sensations  of  violet,  red,  and 
green  as  produces  white. 


Fto.  4S0.— When  looked  •(with  OM  eye,  the  ltaMar«nB««r*OdMiiict  at  one  time;  this  is  in 
Dwt  owinff  to  aatteiiMtiMii,  bat  in  part  sIm  to  insMlitjr  to  Mooumottete  pert ecUy  MMrt 
from  any  deteotoTthie  kind  tormon  than*  very  UmiMd  •!«•.  When  Tiewed  with  botti 
eyea,  a  number  of  ourioiia  phenomena  mar  be  obaerved,  the  explanation  ot  whkih  we 
leave  the  atudent  to  worit  ooft  tor  himaelf(iiner  BefMtrin). 

lOiooMfftlau  M  to  tlM  Oompanti?*  Um,  et&,  of  Ol^feeti.— A 
glance  at  Figs.  430  and  431  will  illustrate  some  surprising 
peculiarities.    On  a  clear  day  distant  mountains  appear  nearer, 


no.  at.— niurtntee  tlluaiona  aa  to  iiae.   In  A  the  height  aeeme  at  flnt  greater  than  the 

breadth,  though  thejr  are  Mual :  the  nitr — "    ~  

Oan  eitiier  a?«he  odban  (after  BmMtetai). 


tareadthj^^u{ii;h  thejT^ra  eouil ;  the  retene  hi  B ;  whfle  0  appears  to  cover  a  leas  area 


VISION. 


591 


g.,  let  violet 
retina  soon 

d  and  green 
a  color  the 

knd  so  on  till 

)let,  red,  and 


from  being  seen  better.  The  full  moon  looks  larger  when  near 
the  horizon  than  when  overhead,  from  the  absence  of  objects  in 
the  latter  case  with  which  to  compare  it ;  and  in  like  manner 
distances  on  the  water  or  on  a  vast  plain  seem  less  than  they 
really  are ;  and  so  in  innumerable  instances  the  influence  of  a 
standard  of  comparison  or  its  absence  is  evident. 

BaljeetiTe  Phwuwiena. — When  the  eyelids  are  shut  in  a  dark 
room,  the  eye  does  not  seem  absolutely  devoid  of  light.  Such 
sensation  of  luminosity  as  may  be  feebly  present  is  sometimes 
spoken  of  as  the  "proper,  light  of  the  retina."  When  the  ball 
of  the  eye  is  pressed  upon,  colored  circles  of  light  appear  when 
the  eyes  are  closed,  such  being  plainly  due  to  mechanical  stimu- 
lation of  the  retina.  These  are  "  phosphenes,"  and  are  akin  to  the 
stare  seen  when  the  eye  receives  a  sudden  blow,  or  to  the  sen- 
sations excited  by  electrical  stimulation.  But,  apart  from  any 
stimulation  of  the  retina,  objects  may  apparently  be  seen  in  ex- 
cited conditions  of  the  brain,  as  in  insanity,  delirium  tremens, 
etc.  Sometimes  one  object,  instead  of  being  recognized,  seems 
to  arouse  the  perception  of  another.  The  cause  is  traceable  in 
many  cases  solely  to  the  brain  itself,  especially  the  part  of  the 
cerebral  cortex  concerned  in  vision,  and  illustrates  the  impor- 
tance of  this  part  of  the  6entral  visual  mechanism,  and  much 
more  into  which  we  can  not  enter  now. 


iMtfane;  this  is  in 
ito  peif  ««Uy  MMUt 

■Uon  nt  which  we 


if  01|)eeti.— A 

e  surprising 
ppear  nearer, 

0 


t  graater  than  the 
o  cover  »  Vem  are* 


CO-ORDINATIOM  OF  THB  TwO  EY*8  IN  VISION. 

As  a  matter  of  fact,  we 
are  aware  that  an  object 
va»Y  be  seen  as  one  either 
with  a  single  eye  or  with 
both.  For  bmoctilcvr  vis- 
ion it  may  be  shown  that 
the  images  formed  on  the 
two  retinas  must  fall  in- 
variably on  corresponding 
points. 

The  position  of  the  lat- 
ter may  be  gathered  from 
Fig.  432.  It  will  be  noticed 
that  the  mcUar  side  of  one 
eye  corresponds  to  the  na- 
sal side  of  the  other, 
though  upper  always  an- 


Wn.4m.- 


.  Ml— Dtamm  to  ffluetrste  cerwpoaMm  pointa 
(after  fMfaHr).  L,  B,  left  and  risht  tmt'a^^, 
are  poliita  ia  0M«7e  oomqioMiiiK  to  a,,  6^  c., 
intheothM'.  The  lower  flmnaareiwoJectlonB  of 
a»  rattaa  of  the  rliidit (Stand  tlie  laft(£)ey». 
It  ni«r  be  ofaaenred  Oat  ttie  malar  ride  of  one 
retina  ootreaponde  to  the  naMi  ride  of  the  other. - 


-'■^^^"""•■n 


ytam 


MM 


592 


ANIMAL  PHYSIOLOGY. 


'X  - 


swers  to  upper  and  lower  to  lower.  This  may  also  be  made 
evident  if  two  saucers  (representing  the  fundus  of  each  eye)  be 
laid  over  each  other  and  marked  off,  as  in  the  figure. 

That  such  corresponding  points  do  actually  exist  may  be 
shown  by  turning  one  eye  so  that  the  image  shall  not  fall,  as 
indicated  in  the  figure.  Only  now  and  then,  however,  is  a  per- 
son to  be  found  who  can  voluntarily  accomplish  this,  but  it 
occurs  in  all  kinds  of  natural  or  induced  squint,  as  ia  alcohol- 
ism, owing  to  partial  paralysis  of  some  of  the  ocular  muscles. 
We  are  thus  naturally  led  to  consider  the  action  of  these  muscles. 

Oeolar  ]lo?«iiMiiitt. — Upon  observing  the  movements  of  an 
individual's  eyes,  the  head  being  kept  stationary,  it  may  be 
noticed  that  (1)  both  eyes  may  converge ;  (9)  one  diverge  and 
the  other  turn  inwuxl ;  (3)  both  move  upward  or  downward ; 


fla.  AS.— View  of  Uw  two  ejet  and  reUtod  parti  (after  Hdmtaolta). 

(4)  these  movements  may  be  accompanied  by  a  certain  degree 
of  rotation  of  the  eyeball. 

The  eye  can  not  be  rotated  around  a  horizontal  axis  without 
combining  this  movement  with  others.  To  accomplish  the 
above  movements  it  is  obvious  that  certain  muscles  of  the  six 
with  which  the  eye  is  provided  must  work  in  harmony,  both  as 
to  the  direction  and  degree  of  the  movement — ^i.  e.,  the  move- 
ments of  the  eyes  ure  affected  by  very  nice  muscular  co-ordina- 
tions. 


VISION. 


698 


Iso  be  made 

each  eye)  be 

•e. 

xist  may  be 

1  not  fall,  as 

ver,  is  a  per- 

this,  but  it 
» in  alcohol- 
liar  muscles, 
lese  muscles, 
nents  of  an 
',  it  may  be 
diverge  and 

downward ; 


torn. 

rtain  degree 

axis  without 
omplish  the 
les  of  the  six 
lony,  both  as 
J.,  the  move- 
%r  co-ordina- 


We  may  speak  of  that  position  of  the  eye  when,  with  the 
head  vertical  in  the  standing  position,  the  distant  horizon  is 
viewed    as    the    primary 
position  and  all  others  as 
secondary  positions. 

Fig.  434  is  meant  to 
illustrate  diagrammatical- 
ly  the  movements  of  the 
eyeball. 

While  the  several  recti 
muscles  elevate  or  depress 
the  eye,  and  turn  it  inward 
or  outward,  and  the  oblique 
muscles  rotate  it,  the  move- 
ments ^produced  by  the  su- 
perior and  inferior  recti 
are  always  corrected  by  the 
assistance  of  the  oblique 
muscles,  since  the  former 
lend  of  themselves  to  turn 
the  eye  somewhat  inward. 
In  like  manner  the  oblique 
muscles  are  corrected  by 
ihe  recti.  ThefoUowingtab- 
ular  statement  will  express 
the  conditions  of  muscular 
contraction  for  the  various 
movements  of  the  eye : 


Tia.  4B4.— Dtagram  intended  to  Ulnatrate  actioii  of 
ejctrimlo  ocular  mueotea  (after  Fick).  The  heavy 
Uoea  repreaent  the  mn«ilea  of  Uie  eyeball,  and 
tha  line  linea  the  azato  b/ movement 


Straight 
move- 
ments. 


Oblique 
move- 
monts. 


Eleyfttion Rectus  superior  and  obliquus  inferior. 

Depression Rectus  inferior  and  obliquns  superior. 

Adduction  to  nasal  side. .  .Rectus  intemus. 

Adduction  to  malar  side..  .Rectus  extemus. 

'  Elevation  witli  adduction.. Rectus  superior  and  intemus,  with  obli- 
quus inferior. 

Depression  with  adduction.Reotus  inferior  and  internus  with  obliquus 

superior. 

Elevation  with  abduction. .  Rectus  superior  and  extemus  with  obliquus 

inferior. 

Depression  with  abduction.Rectus  inferior  and  extemus,  with  obliquus 

superior. 

What  is  the  nervous  mechanism  by  which  these  "associ- 
ated "  movements  of  the  eyes  are  accomplished  ?  It  has  been 
found,  experimentally,  that  when  different  parts  of  the  corpora 
quadrigemina  are  stimulated,  certain  movements  of  the  eyes 

88 


^.^tgy.--  •  >i  liwjJtiiiaiii.irtiWhiftftiiWW 


5M 


ANIMAL  PHYSIOLOGY. 


s: 


follow.    Thus,  stimulation  of  the  right  side  of  the  nates  leads 
to  movements  of  both  eyes  to  the  left,  and  the  reverse  when 

the  opposite  side  is  stimulated ;  also, 
stimulation  in  the  middle  line  causes 
convergence  and  downward  move- 
ment, etc.,  with  the  corresponding 
movements  of  the  iris.  Since  section 
of  the  nates  in  the  middle  line  leads 
to  movements  confined  to  the  eye  of 
the  same  side,  the  center  would  ap- 
pear to  be  double.  However,  it  may  be 
that  the  cells  actually  concerned  do 
not  lie  in  the  corpora  quadrigemina, 
but  below,  or  outside  of  them.  The  localization  is  as  yet  in- 
complete, f 

The  Horoptar. — If  we  hold  up  one  finger  before  another,  in 
front  of  both  eyes,  when  the  accommodation  is  made  for  the 
one  the  other  will  appear  double,  owing  to  the  images  not  fall- 
ing on  corresponding  parts  of  the  retina ;  for,  if  one  eye  be 
closed,  one  of  the  images  disappears. 

Another  way  of  putting  the  matter  is,  to  say  that  the  objects 
in  the  field  under  consideration  do  not  lie  in  the  horopter.    The 


n*.  4B.— Diagi«m  to  IBaitrate  de- 
on«attoD  of  flben  in  tiie  op- 
tie  QominlMun  of  naa  (•fttr 
FUnL) 


rw.  4M.—TIM  honvtor  (aflar  Le  Canto).   Wbaa  tiw  «;«■  an  dlnetod  to  the  potot  it  in  the 
oindo,  imagw  (Tom  any  otiier  part  of  It  (■•  D)  CtU  on  oomaponding  polnia  of  Hw  retina. 

latter  is  that  arrangement  of  points  in  space  from  which  rays 
fall  on  corresponding  (identical)  parts  of  the  retina.    It  must 


le  nates  leads 
reverse  when 
lulated;  also, 
le  line  causes 
iward  move- 
orresponding 
Since  section 
die  line  leads 
to  the  eye  of 
er  would  ap- 
yer,  it  may  be 
Boncemed  do 
uadrigemina, 
1  is  as  yet  in- 

'e  another,  in 
made  for  the 
iges  not  fall- 
f  one  eye  be 

at  the  objects 
>ropter.    The 


) 


sthe  point  il  in  tbo 
iaitm  of  HW  retina. 


n  which  rays 
dna.    It  must 


VISION. 


696 


vary  with  the  position  of  the  eyes,  head,  etc.,  and  often  consti- 
tutes a  very  complex  geometrical  figure  when  the  various 
points  are  united.  The  simpler  case  is  when  standing  upright 
we  look  toward  the  distant  horizon,  in  which  instance  the 
horopter  forms  a  plane  drawn  beneath  us — i.  e.,  is  the  ground  on 
which  we  stand.    This  will  appear  from  Fig.  436. 

Iitimatimi  of  the  Sin  and  IMitaiMe  of  Ol^eoti.— The  processes 
by  which  we  form  a  judgment  of  the  size  and  distance  of  objects 
are  closely  related. 

As  we  have  already  shown  (page  683),  the  visual  angle  varies 
both  with  the  size  and  the  distance  of  an  object.  Knowing 
that  two  objects  are  at  the  same  distance  from  the  eye,  we  esti- 
mate that  the  one  is  larger  than  the  other  when  the  image  one 
forms  on  the  retina  is  larger,  or  when  the  visual  angle  it  sub- 
tends is  greater  than  in  the  other  case,  and  conversely.  Thus, 
knowing  that  two  persons  are  at  the  distance  of  hedf  a  mile 
away,  if  one  is  judged  by  us  to  be  smaller  than  the  other,  it 
will  be  because  the  retinal  image  corresponding  to  the  object 
is  smaller,  other  things  being  equal.  But  thd  subject  is  n.ore 
complex  than  might  be  inferred  from  these  statements. 

We  have  already  pointed  out  that  objects  of  a  certain  color 
seem  nearer  than  others ;  also  those  that  are  brighter,  as  in  the 
case  of  mountains  on  a  clear  day.  And  not  only  do  all  the 
qualities  of  the  image  itself  enter  as  data  into  the  construction 
of  the  judgment,  but  numerous  muscular  sensations.  The  eyes 
accommodating  and  converging  for  near  objects,  from  the  law 
of  association,  give  rise  to  the  idea  of  nearness,  for  habitually 
such  takes  place  when  near  objects  are  viewed,  so  that  the 
subject  becomes  very  complex.  That  we  judge  imperfectly  of 
the  position  of  an  object  with  but  one  eye  is  realized  on  attempt- 
ing to  stick  a  pin  into  a  certain  small  spot,  thread  a  needle,  cork 
a  small  bottle,  etc.,  when  one  eye  is  closed. 

SoUditj. — By  the  use  of  one  eye  alone  we  can  form  an  idea  of 
the  shape  of  a  solid  bod;- ;  though,  in  the  case  of  such  as  are  very 
complex,  this  process  is  felt  to  be  both  laborious  and  imperfect. 

From  the  limited  nature  of  the  visual  field  for  distinct 
vision,  it  follows  that  we  can  not  with  one  eye  see  equally  dis- 
tinctly all  the  parts  of  a  solid  that  is  turned  toward  us.  After 
a  little  practice  one  may  learn  to  define  for  himself  what  he 
actually  does  see. 

Such  a  figure  as  that  following  results  from  the  combina- 
tion, meTUaUy,  of  two  others,  which  answer  to  the  images  fall- 
ing on  the  right  and  on  the  left  eyes  respectively. 


»'aiMlitlllMila 


696 


ANIMAL  PHYSIOLOGY. 


,      In  order  that  such  fusion  shall  take  place,  the  respective 
images  must  fall  on  identical  (corresponding)  parts  of  the  retina. 


V 

V 

i 

K — "PY 

1     1 

A 

A 

/ 

m 

r              n 

hS  hSdoeiTOiiSCTSrty  over  the  llguw,  the  image  fomwd  to  tte  right  eyewhen^ 
Btto  ctosat  fl^wd  ra  tte  righCwd  lh«t  SeiTwheii  U»  right  eye  tojsW  to  rep- 
SLnted  tSthS  fflSrtatlSrmflffi.  No  MpenxMitioa  of  theee  figures  wffl  give  P,  yrt 
'Tl  wSd*!  pwoSJSey  «S^combtoed  toto  PrSeflgure  m  it  wpem  to  both  eye*  (•fter 


As  is  well  known,  the  pictures  used  for  stereoscopes  give 
different  views  of  the  one  object,  as  represented  on  a  flat  sur- 
face. These  are  thrown  upon  corresponding  points  of  the  retina 
by  the  use  either  of  prisms  or  mirrors,  when  the  idea  of  solidity- 
is  produced.  As  to  whether  movements  of  the  eyes  (converg- 
ence) are  necessary  for  stereoscopic  vision  is  disputed.  It  has 
been  inferred,  from  the  fact  that  objects  appear  solid  during 
an  electric  flash,  the  duration  of  which  is  far  too  short  to  per- 
mit of  movements  of  the  ocular  muscles,  that  such  movements 
are  not  essential.  The  truth  seems  to  lie  midway ;  for  while 
simple  figures  may  not  require  them,  the  more  complex  do,  or, 
at  all  events,  the  judgment  is  very  greatly  assisted  thereby.  It 
is  of  the  utmost  importance  to  bear  in  mind  that  all  visual 
judgments  are  the  result  of  many  processes,  in  which,  not  the 
sense  of  vision  alone,  but  others,  are  concerned ;  and  the  mutual 
dependence  of  one  sense  on  another  is  great,  probably  beyond 
our  powers  to  estimate.  Reference  has  been  made  to  this  sub- 
ject previously. 

pROTKCTivB  Mechanisms  of  the  Eye. 

The  eyelids  have  been  appropriately  compared  to  the  shut- 
ters of  a  window.  They  are,  however,  not  impervious  to  light, 
as  any  one  may  convince  himself  by  noticing  that  he  can  locate 
the  position  of  a  bright  light  with  the  eyes  shut ;  also  that  a 
sensitive  person  (child)  will  turn  j  y  (reflexly)  from  a  light 
when  sleeping  if  it  be  suddenly  bro  ight  near  the  head.  The 
Meibomian  glands,  a  modification  of  the  sebaceous,  secrete  an 
oily  substance  that  seems  to  protect  the  lids  against  the  lachry- 


■■IHP 


'r^-Trrr 


VISION. 


597 


ihe  respective 
3  of  the  retina. 


«  looked  at  wltli  tbo' 
e  right  ey«  when  the 
eye  is  cioaed  la  rep- 
gures  will  give  P,  yet 
n  to  both  eyes  (sner 


reoscopes  give 
on  a  flat  sar- 
ts  of  the  retina 
idea  of  solidity 
eyes  (converg- 
iputed.  It  has 
^r  solid  during 
•o  short  to  per- 
ich  movement's 
inray;  for  while 
complex  do,  or, 
ed  thereby.  It 
that  all  visual 
which,  not  the 
md  the  mutual 
robably  beyond 
ode  to  this  sub- 


red  to  the  shut- 
rvious  to  light, 
Eit  he  can  locate 
mt ;  also  that  a 
y)  from  a  light 
the  head.  The 
eous,  secrete  an 
inst  the  lachry- 


mal fluid,  and  prevents  the  latter  running  over  their  edges  as 
oil  would  on  the  margins  of  a  vessel.  The  lachrymal  gland  is 
not  in  structure  unlike  the  parotid,  the  secretion  of  which  its 
own  somewhat  resembles. 

The  saltness  of  the  tears,  owing  to  abundance  of  sodium 
chloride,  is  well  known  to  all.  The  nervous  mechanism  of  se* 
cretion  of  tears  is  usually  reflex,  the  stimulus  coming  from  the 
action  of  the  air  against  the  eyeball  or  from  partial  desiccation 
owing  to  evaporation.  When  the  eyeball  itself,  or  the  nose,  is 
irritated,  the  afferent  nerves  are  the  branches  of  the  fifth,  to 
which  also  belong  the  efferent  nerves.  The  latter  include  also 
the  cervical  sympathetic.  But  it  will,  of  course,  be  understood 
that  the  afferent  impulses  r •  'be derived  through  a  large  num- 
ber of  nerves,  and  that  i.  >  acreting  cen- 
ter may  be  acted  upon  directly  by  the 
cerebrum  (emotions).  The  excess  of  lach- 
rymal secretion  is  carried  away  by  the 
nasal  duct  into  which  the  lachrymal 
canals  empty.  While  it  is  well  known 
that  closure  of  the  lids  by  the  orbicularis 
muscle  favors  the  removal  of  the  fluid, 
the  method  by  which  the  latter  is  ac- 
complished is  not  agreed  upon.  Some 
believe  that  the  closure  of  the  lids  forces 
the  fluid  on  through  the  tubes,  when 
they  suck  in  a  fresh  quantity ;  others  that 
the  orbicularis  drives  the  fluid  directly 
through  the  tubes,  kept  open  by  muscu- 
lar arrangements;  and  there  are  several 
other  divergent  opinions.  The  prevention  of  winking  leads  to 
irritation  of  the  eye,  which  may  assume  a  serious  character,  so 
that  the  obvious  use  of  the  secretion  of  tears  is  to  keep  the  eye 
both  moist  and  clean. 

Special  Considerations. - 

OompantiTS.— It  seems  to  be  established  that  certain  animals 
devoid  of.  eyes,  as  certain  myriopods,  are  able  to  perceive  the 
presence  of  light,  even  when  the  heat-rays  are  cut  off.  The  most 
rudimentary  beginning  of  a  visual  apparatus  appears  to  be  a 
mass  of  pigment  with  a  nerve  attached,  as  in  certain  worms ; 
though  it  is  questionable  whether  mere  collections  of  pigment 
without  nerves  may  not  in  some  instances  represent  still  earlier 


UushirnuU  ma,  uid  i 
CMIM,  opened   from  ths 


fRiBt  (after  Bappeyj, 


698 


ANIMAL  PHTSI0L06T. 


mdimentB  of  our  eyes.  Among  invertebrates,  eyes  may  in  gen- 
eral be  divided  into  two  classes :  1.  The  compound  or  faceted 
eyes,  the  structure  of  which  may  be  gathered  from  the  accom- 
panying figures.  It  will  be  noted  that  in  such  the  retina  is  con- 
vex, and  is  made  up  of  large  compound  nerve-rods  {retinulce), 
separated  from  one  another  by  pigment-sheaths.    The  picture 


r 


Fio.  MQ. 


Fie.  440. 

no.  48B.— DiMmamMtio  mmwntetion  of  ooinpouiid  ejre  In  an  Arthropod  (ultet  Clwis}.  C, 
oarat»;K,cmUaSaf»  S^iP,  pigBMnt;  R,  nerve-rod*  of  raUna;  Fb,  layer  of  flber*; 
Os,  layer  of  gai^^ion  oelli ;  ly,  retinal  libera :  Fie,  croaring  of  libera. 

Sto.  4W.— Three  ftMseta  with  retfatute  fironi  componnd  ejre  oC  oodtdiafer  (after  Orenaoher). 
Pigment  haa  been  dlaMlved  away  from  two  of  the  (koeta.  F,  corneal  facet ;  JT.onntalllne 
•one;  i>,  pigmeot-aheaUi ;  P',  chief  pigment-oell ;  P",  pigmeat^sella  of  aeooad  order; 
R,  retlnuUB. 

formed  by  snjh  eyes  must  represent  a  sort  of  m(»aic,  and  be 
I'atucr  aedcient  in  definition  and  brightness.  It  will  be  noticed 
that  in  such  eyes,  both  the  cornea  and  crystalline  lens  of  verte- 
brates are  represented  in  multiple  form.  This  form  of  eye  is 
found  in  crustaceans  and  some  insects.  2.  The  simple  eye  pre- 
vails among  annelids,  insects,  arachnids,  moUusks,  and  verte- 
brates. A  more  advanced  form  of  such  a  visual  organ  is  found 
in  the  cuttle-fish.  It  may  be  seen  (Fig.  443)  that  such  an  eye 
corresponds  fairly  well  with  the  eye  of  a  vertebrate. 

The  eye  of  the  fish  is  characterized  by  flatness  of  the  cornea ; 


■Mi^»n«liiMiii>i"a 


mi^mti^wMn.iitAmiaitm'tmit « 


iosaic,  and  be 
ill  be  noticed 
lens  of  verte- 
trm  of  eye  is 
nple  eye  pre- 
»,  and  yerte- 
rgan  is  found 
t  saob  an  eye 
fce. 
}ftlie  cornea; 


000 


ANIMAL  PHYSIOLOGY. 


organ  known,  is  of  peculiar  shape  as  a  whole,  presenting  a  large 
posterior  surface  for  retinal  expansion ;  a  very  convex  cornea, 
a  highly  develojied  lens,  an  extremely  movable  iris;  eyelids 
and  a  nictitating  membrane  (third  eyelid),  which  may  be  made 
to  cover  the  whole  of  the  exposed  part  of  the  eye,  and  thus 
shield  screen-like  from  excess  of  light ;  ossifications  of  the  scle- 
rotic ;  a  structure  which  is  a  peculiar 
modification  of  the  choroid,  of  which  it 
is  a  sort  of  offshoot  and  like  it  very 
vascular,  answering  to  the  falciform 
process  of  the  eye  of  the  fish  and  the 
reptile.      Prom   its  appearance  it   is 
termed  the  pecten.    Birds,  on  account 
of  a  highly  developed  ciliary  muscle, 
possess  wonderful  powers  of  accommo- 
dation, rendered  important  on  account 
of  their  rapid  mode  of  progression. 
They  also  seem  to  be  able  to  alter  the 
size  of  the  pupil  at  will. 

Brolntimi. — From  the  above  brief  ac- 
count of  the  eye  in  different  grades  of 
animals,  it  will  appear  that  its  modifi- 
cations answer  to  differences  in  the 
environment. 

Adaptation  is  evident.  Darwin  believes  this  to  have  been 
effected  partly  by  natural  selection — ^i.  e.,  the  survival  of  the 
animal  in  which  the  form  of  eye  appeared  best  adapted  to  its 
needs,  and  partly  by  the  use  or  disuse  of  certain  parts. 

The  latter  is  illustrated— 1.  By  the  blind  fishes,  insects,  etc., 
of  certain  caves,  as  those  of  Kentucky ;  and  it  is  of  extreme  in- 
terest to  note  that  various  grades  of  transition  toward  complete 
blindness  are  observable,  according  to  the  degree  of  darkness  in 
which  the  animal  is  found  living,  whether  wholly  within  the 
cave  or  where  there  is  still  some  light.  A  crab  has  been  found 
with  the  eye-stalk  still  present,  but  the  eye  itself  atrophied. 
Again,  animals  that  burrow  seem  to  be  in  process  of  losing 
their  eyes,  through  inflammation  from  obvious  causes ;  and  some 
of  them,  as  the  moles,  have  the  eye  still  existing,  though  well- 
nigh  or  wholly  covered  with  skin.  Internal  parasites  are  often 
without  eyes.  It  is  not  difficult  to  understand  how  one  bird  of 
prey,  with  eyes  superior  to  those  of  its  fellows,  would  gain 
supremacy,  and,  in  periods  of  scarcity,  survive  and  leave  off- 
spring when  others  would  perish. 

( 


¥ia.  448.— Biye  of  noetunuU  bird 
or  prey  (after  Wiederriwim). 
Co,  come* :  L,  lens :  JM,  ret- 
ina :  P.  pecten  ;  No,  opUc 
nerre ;  8e,  oMiflcatkm  of  acle- 
rptlo  coat ;  CM,  etttary  mus- 
cle. Birda  have  unuanally 
keen  Tiaion,  Rrrat  power  of 
accommodation,  and  eztreme 
mobiUty  of  the  iris. 


Eite^«3S^s;SeTSa^»*&^t^*s*J»*«l»«««w^'«*^--- 


VISION. 


601 


enting  a  large 
onvex  cornea, 

iris;  eyelids 
may  be  made 
eye,  and  thus 
ns  of  the  scle- 
is  a  peculiar 
d,  of  which  it 
i  like  it  very 
the  falciform 
)  fish  and  the 
)arance  it  is 
8,  on  account 
liary  muscle, 
of  accommo- 
it  on  account 

progression, 
e  to  alter  the 

bove  brief  ac- 
ent  grades  of 
it  its  modifi- 
snces  in  the 

to  have  been 
vival  of  the 
adapted  to  its 
arts. 

,  insects,  etc., 
f  extreme  in- 
ard  complete 
f  darkness  in 
ly  within  the 
8  been  found 
If  atrophied. 
)ss  of  losing 
es ;  and  some 
though  well- 
ites  are  often 
V  one  bird  of 
would  gain 
id  leave  off- 


It  is,  of  course,  impossible  to  trace  each  step  by  which  the 
vertebrate  eye  has  been  developed  from  more  rudimentary 
forms,  though  the  data  for  such  an  attempt  have  greatly 
accumulated  within  the  last  few  years ;  and  it  is  not  to  be  for- 
gotten that  even  t1ie  vertebrate  eye  has  many  imperfections, 
so  that  no  doctrine  of  complete  adaptation,  according  to  the 
argument  from  design  as  usually  understood,  can  apply. 

Certain  acquired  imperfections  of  the  eye  seem  to  be  multi- 
plying at  the  present  day,  such  as  myopia,  weakness  of  the 
accommodative  mechanism,  etc.  The  excessive  use  of  the  eyes, 
necessitating  undue  exercise  of  this  apparatus  or  strain  of  the 
accommodation,  is  the  fruitful  source  of  evil.  A  good  light — 
that  is,  one  both  sufficient  in  quantity  and  falling  in  the  right 
direction  upon  the  eyes  and  the  objects  to  be  viewed,  together 
with  adequate  ventilation  of  the  rooms  occupied — is  of  great 
importance,  though,  as  in  the  case  of  other  organs,  it  is  impos- 
sible to  avoid  wholly  the  penalties  of  over-use  of  the  visual 
apparatus. 

It  is  of  great  importance  to  recognize  that  what  we  really 
see  depends  more  upon  the  brain  and  the  mind  than  the  eye. 
If  any  one  will  observe  how  frequent  are  his  incipient  errors 


BrattnOime 
flMdiiOa 


Cmtre  in  rtgton  tf^~ 
carp,  quaOrigemina 


-Cortical  eentn 


i-Centre  (n  optic  OuOamm 


Fia.  444.— Diagram  intended  to  Htaatrate  the  elaboration  of  Tinial  impulaea,  beoinninK  In 
reUna  and  culmlnaWng  in  the  cerebral  cortex.  Ooune  of  impidaea  is  Indicated  brarruwa. 
Knowledge  of  auditory  centers  ia  not  yet  exact  enou^  to  permit  of  the  conatmction  d*  a 
diagram,  thouirh  doubtleaa  eventnaUx  the  central  proceMee  will  be  looaliaed  as  with  vtainn. 
The  latter  remark  appUea  to  the  other  aenaea  to  nearly  the  aaiDo  extent,  poariUy  quite  aa 
much. 


MiiBWWKU^'i+i'J^-WrVtC'J.iJM^n-'-'S  >..ip^»'«» 


I 


608 


ANIMAL  PHYSIOLOGY. 


of  vision  speedily  corrected,  he  will  realize  the  truth  of  the 
above  remark.  Precisely  the  same  data  furnished  by  the  eye 
are  in  one  mind  worked  up  in  virtue  of  past  experience  (educa- 
tion) into  an  elaborate  conception,  while  to  another  they  an- 
swer only  to  certain  vague  forms  and  colors.  And  herein  lies 
the  great  superiority  of  man's  vision  over  that  of  all  other 
animals. 

Within  the  limits  of  their  mental  vision  do  all  creatures  see. 
Man  has  not  the  keen  ocular  diisoriminating  power  of  the  ha  >rk ; 
he  can  neither  see  so  far  nor  so  clearly ;  nor  has  he  the  wide 
field  of  vision  of  the  gazelle ;  but  he  has  the  mental  resource 
which  enables  him  to  make  more  out  of  the  materials  with 
which  his  eyes  furnish  him.  It  is  by  virtue  of  his  higher  cere- 
bral development  that  he  has  added  to  his  natural  eyes  others 
in  the  microscope  and  telescope,  which  none  of  Nature's  forms 
can  approach. 

PathflloflwJ. — ^There  may  be  ulceration  of  the  cornea,  inflam- 
mation of  this  part,  or  various  other  disorders  which  lead  to 
opacity.  The  low  vitality  of  this  region,  probably  owing  to 
absence  of  blood-vessels,  is  evidenced  by  the  slowness  with 
which  small  ulcers  heal.  Opacity  of  the  lens  (cataract)  when 
complete  causes  blindness,  which  can  be  only  partially  reme- 
died by  removal  of  the  former.  Inflammations  of  any  part  of 
the  eye  are  serious,  from  possible  adhesions,  opacities,  etc.,  fol- 
lowing. Should  such  be  accompanied  by  great  excess  of  intra- 
ocular tension,  serious  damage  to  the  retina  may  result.  Of 
course,  atrpphy  of  the  optic  nerve  (due  to  lesions  in  the  brain, 
etc.)  is  irremediable,  and  involves  blindness.  Inspection  of  the 
internal  parts  of  the  eye  (fundus  oculi)  often  reveals  the  first 
evidence  of  disease  in  remote  parts,  as  the  kidneys. 

From  what  has  been  said  of  the  movements  of  the  two  eyes 
in  harmony,  etc.,  the  student  might  be  led  to  inf^r  that  disease 
of  one  organ,  in  consequence  of  an  evident  close  connection  of 
the  nervous  mechanism  of  the  eyes,  would  be  likely  to  set  up 
a  corresponding  condition  in  the  other  unless  speedily  checked. 
Such  is  the  case,  and  is  at  once  instructive  and  of  great  prac- 
tical moment. 

Paralysis  of  the  various  ocular  muscles  leads  to  squinting, 
as  already  noticed. 

Brief  Sjnopiit  «f  the  Phyiiokgy  of  Yinon.— All  the  other  parts 
of  the  eye  may  be  said  to  exist  for  the  retina,  since  all  are  re- 
lated to  the  formation  of  a  distinct  image  on  this  nervoi  s  ex- 
pansion.   The  principal  refractive  body  is  the  crystalline  lens. 


VISION. 


608 


truth  of  the 
d  by  the  eye 
ience  (educa- 
/her  they  an- 
d  herein  lies 
of  all  other 

creatures  see. 
of  thoha>rk; 
i  he  the  wide 
ntal  resource 
aterials  with 
i  higher  cere- 
al eyes  others 
ature's  forms 

ornea,  inflam- 
rhich  lead  to 
bly  owing  to 
lowness  with 
itaract)  when 
u^ially  reme- 
if  any  part  of 
ities,  etc.,  fol- 
ccess  of  intra- 
ky  result.  Of 
I  in  the  brain, 
pection  of  the 
iveals  the  first 

B. 

f  the  two  eyes 
tr  that  disease 
connection  of 
kely  to  set  up 
Bdily  checked. 
>f  great  prac- 

I  to  squinting, 

he  other  parts 
nee  all  are  re- 
is  nervoi  s  ex- 
ystalline  lens. 


The  iris  serves  to  regulate  the  quantity  of  light  admitted  to 
the  eye,  and  to  cut  oflf  too  divergent  rays.  In  order  that  objects 
at  different  distances  may  be  seen  distinctly,  the  lens  alters  in 
shape  in  response  to  the  actions  of  the  ciliary  muscle  on  the 
suspensory  ligament,  the  anterior  surface  becoming  more  con- 
Accommodation  is  associated  with  convergence  of  the 


vex. 

visual  axes  and  contraction  of  the  pupil.  The  latter  has  circu- 
lar and  radiating  plain  muscular  fibers  (striped  in  birds,  that 
seem  to  be  able  to  alter  the  size  of  the  pupil  at  will),  governed 
by  the  third,  fifth,  and  sympathetic  nerves.  Contraction  of 
the  pupil  is  a  reflex  act,  the  nervous  center  lying  in  the  front 
part  of  the  floor  of  the  aqueduct  of  Sylvius,  while  the  action 
of  the  other  center  (near  this  one)  through  the  sympathetic 
nerve  is  tonic. 

Accommodation  through  the  ciliary  musclo  is  governed  by 
a  center  situated  in  the  hind  ■■-  art  of  the  floor  r.t  the  third  ven- 
tricle near  the  anterior  bundl'.s  of  the  third  nerve,  which  latter 
is  the  medium  of  the  change.  There  are  certain  imperfections 
common  to  all  human  eyes,  such  uti  sph  jrical  and  cbjomatic 
aberration,  a  limited  degree  oi  astign?-  ism,  etr  Whtii  rays 
of  light  are  focused  anterior  to  the  retina,  the  < ;  e  is  myopic ; 
when  posterior  to  it,  hyperimetropic. 

The  presbyopic  eye  is  one  in  which  +he  mecaanism  of  ocom- 
modation  is  at  fault,  chiefly  the  cilie  y  -ouscle.  The  i  >ait  of 
entrance  of  the  optic  nerve  (blind-sp  t)  is  insensible  to  light ; 
and  visual  impulses  can  be  shown  to  originate  in  the  layers  of 
rods  and  cones,  probably  through  stimulation  from  chemical 
changes  effected  by  light  acting  on  the  retina.  The  sensation 
outlasts  the  stimulus ;  hence  positive  after-images  occur.  Nega- 
tive after-images  occur  in  consequenc  <^f  excessive  stimulation 
and  exhaustion  of  the  retina,  or  disorder  of  the  chemical  pro- 
cesses that  excite  visual  impulses.  When  stimuli  succeed  one 
another  with  a  certain  degree  of  rapidity,  sensation  is  continu- 
ous. The  eye  can  distinguish  degrees  of  light  within  certain 
limits,  varying  by  about  j^  of  the  total. 

Objects  become  fusee  ;"  are  seen  as  one  when  the  rays  from 
them  falling  on  the  retiL-  *  pproximate  too  closely  on  that  sur- 
face. The  brain,  as  well  as  the  eye  itself,  is  concwmed  in  such 
discriminations,  the  former  probably  more  than  the  latter.  The 
various  color  sensatlous  we  have  are  the  result  either  of  definite 
single  sensationp  Oi  the  fusion  physiologically  of  two  or  more 
of  these,  and  have  no  reference  to  the  fusion  of  pigments  ex- 
ternal to  the  eye.    All  human  eyes  are  to  some  extent  color- 


.-rtisx 


Ill  wiw  f^nnni'itmt'ttm 


604 


ANIMAL  PHYSIOLOGY. 


blind  in  the  sense  that  it  is  probable  that  other  animals  (ant!9, 
etc.)  can  perceive  colors  not  included  in  our  spectrum,  and  also 
in  the  sense  that  all  parts  of  the  retina  are  not  equally  sensitive 
to  rays  of  a  certain  wave-length ;  but  some  persons  are  imable 
to  perceive  certain  colors  at  all. 

The  mactda  lutea,  and  especially  the  fovea  centralis,  are  the 
points  of  greatest  retinal  sensitiveness.  When  the  images  of 
objects  are  thrown  on  these  parts,  they  are  seen  with  complete 
distinctness ;  and  it  is  to  effect  this  result  that  the  movements 
of  the  two  eyes  in  concert  take  place.  An  object  is  seen  as  one 
when  the  position  of  the  eyes  (visual  axes)  is  such  that  the  im- 
ages formed  fall  on  corresponding  parts  of  the  retina.  Binocu- 
lar vision  is  important  to  supply  the  sensory  data  for  the  idea  of 
solidity.  It  is  important  to  remember  that,  before  an  object  is 
"  seen  "  at  all,  the  sensory  impressions  furnished  by  the^  retina 
and  conveyed  inward  by  the  optic  nerve  are  elaborated  in  the 
brain  and  brought  under  the  cognizance  of  the  perceiving  ego. 
We  recognize  many  visual  illusions  and  imperfections  of  vari- 
ous kinds,  the  course  of  which  it  is  difficult  to  locate  in  any 
one  j^rt  of  the  visual  tract,  such  as  are  referred  to  "^irradia- 
tion," "  contrast,"  etc.  There  may  also  be  visual  phenomena 
that  are  purely  subjective,  and  others  that  result  from  sugges- 
tion rather  than  any  definite  sensory  basis  of  retinal  images. 
Hence  what  one  sees  depends  on  his  state  of  mind  at  the  time. 

This  applies  to  appreciation  of  size  and  distance  also,  though 
in  such  cases  we  have  the  visual  angle,  certain  muscular  move- 
ments (muscular  sense),  the  strain  of  accommodation,  etc.,  as 
guides. 


l"^ 


HEABINO. 

As  the  end-organ  of  vision  is  protected  both  without  and 
within,  so  is  the  still  more  complicated  end-organ  of  the  sense 
of  hearing  more  perfectly  guarded  against  injury,  being  in- 
closed within  a  membranous  as  well  as  bony  covering  and  sur- 
rounded by  fluid,  which  must  shield  it  from  stimulation,  except 
through  this  medium. 

Hearing  proper,  as  distinguished  from  the  mere  recognition 
of  jars  to  the  tissues,  can,  in  fact,  only  be  attained  through  the 
impulses  conveyed  to  the  auditory  brain-centers,  as  originated 
in  the  end-organ  by  the  vibrations  of  the  fluid  with  which  it  is 
bathed. 


IPfWt  MrinMMNMIMIMMMlf  311 


HEARING. 


605 


nimals  (ant*;, 
um,  and  also 
ally  sensitive 
18  are  unable 

ralis,  are  the 
be  images  of 
'ith  complete 
e  movements 
s  seen  as  one 
that  the  im- 
na.  Binocu- 
or  the  idea  of 
)  an  object  is 
by  the^  retina 
>rated  in  the 
rceiving  ego. 
tions  of  vari- 
ocate  in  any 
.  to  "  irradia- 
L  phenomena 
from  sugges- 
binal  images, 
at  the  time. 
)  also,  though 
.scular  move- 
ation,  etc.,  as 


without  and 
of  the  sense 
ry,  being  in- 
ring  and  sur- 
lation,  except 

e  recognition 

through  the 

as  originated 

bh  which  it  is 


It  will  be  assumed  that  the  student  has  made  himself  famil- 
iar with  the  general  anatomy  of  the  ear.  The  essential  points 
in  regard  to  sound  are  considered  in  the  chapter  on  "The 
Voice."  It  will  be  remembered  that  what  we  term  a  musical 
tone,  as  distinguished  from  a  noise,  is  characterized  by  the 
regularity  of  vibrations  of  the  air  that  reach  the  ear ;  and  that 
just  as  ethereal  vibrations  of  a  certain  wave-length  give  rise  to 
the  sensation  of  a  particular  color,  so  do  aSrial  vibrations  of  a 
definite  wave-length  originate  a  certain  tone.  In  each  case  must 
we  take  into  account  a  physical  cause  for  the  physiological 
effect,  and  these  bear  a  very  exact  relationship  to  one  another. 

As  will  be  seen  later,  while  in  all  animals  that  have  a  well- 
defined  sense  of  hearing  the  process  is  essentially  such  as  we 
have  indicated  above,  the  means  leading  up  to  the  final  stimu- 
lation of  the  end-organ  are  very  various.  At  present  we  shall 
consider  the  acoustic  mechanism  in  mammals,  with  special  ref- 
erence to  man.    There  are  in  fact  three  sets  of  apparatus :  (1) 


Ito.  MB.— SectlOB  UvoiighwidNarracsaB  (•»•¥- 
•xtemal  Mid  mmUUxt  BMatUB  wtth  0|Miriiig  of 


;  t,  4,  S,  trnfttj  of  oondM, 
.  .        -  _.^      i;  D,in«mbraiuttyinpMii; 

r.antertorpwtariMMi;  S,  nwileua  ;•,  ton*  hMidte  o(  mfikw,  •tlwdted  to  internal  nir- 
^toe of  tympMile mambnuie— it  1»  MW»iwB»Mw»led m  itnaffiy  iiKlr»wii ;  10,  tenaor  tym- 
panl  muacle ;  11,  tpnpuSoeKfHj:  It,  lomclilMi  tube;  IS, mperlor  Mmidrcular  cmwI  : 
14,  jMMterior  aemiolrcular  omwI  ;  IS,  «xtwnal  MMnieiroulMr  cwuu ;  IS,  cochte* ;  17,  Internal 
auditory  meatua;  18,  facial  nerre;  IB,  large  pfetroaal  nerve;  W,  Tcatnmlar  branch  of 
auditory  nerve ;  «1,  codilear  branch  of  Mune. 


one  for  collecting  the  aSrial  vibrations ;  (3)  one  for  transmit- 
ting them ;  and  (3)  one  for  receiving  the  impression  through  a 
fluid  medium ;  in  other  words,  an  external,  ndddle,  and  internal 
ear. 


:i 


606 


ANIMAL  PHYSIOLOGY. 


The  external  ear  in  man  being  practically  immovable,  owing 
to  the  feeble  development  of  its  muscles,  has,  as  compared  with 
such  animals  as  the  horse  or  cow,  but  little  use  as  a  collecting 
organ  for  the  vibrations  of  the  air.  The  meatus  or  auditory 
canal  may  be  regarded  both  as  a  conductor  of  vibrations  and 
as  protective  to  the  middle  ear,  especially  the  delicate  drum- 
head, since  it  is  provided  with  hairs  externally  in  particular, 
and  with  glands  that  secrete  a  bitter  substance  of  an  unctuous 
nature. 

The  KMibnuia  Tymptai  is  concavo^onvex  in  form,  and,  hav- 
ing attached  to  it  the  chain  of  bones  shortly  to  be  noticed,  is 
well  adapted  to  take  up  the  vibrations  communicated  to  it  from 
the  air ;  though  it  also  enters  into  sympathetic  vibration  when 


(•Iter  rUnt  Mid  ~~" ----- 

meiit  of  tendon  „  _  _ 

ins  with  nwDeuB;  IS,  Mterior  pookat ;  18,oliordntynipMUiMr*er^^^^^^^ 


Md  iimM-.o^citiirfflwn  of  trmpulo  mwibrMMri.  Mrma  riii 


tram  within 
withattMdi- 
mallmia ;  7, 


the  bones  of  the  head  are  the  medium,  as  when  a  tuning-fork 
is  held  between  the  teeth.     Ordinary  stretched  membranes 


^»iLiiW]awii^'iJB.LiiiLW]tj>ijTliiiinrr;yW 


WjWpmwfMitii-tnirii 


-    I'WWP— wiwi'w.wm 


HEARING. 


60T 


have  a  fundamental  (self-tone,  proper  tone)  tone  of  their  own, 
to  which  they  respond  more  re»dily  than  to  others. 

If  such  held  for  the  membrana  tympani,  it  is  evident  that 

>»in  tones  would  be  heard  better  than  others,  and  that  when 
ihe  fundamental  one  was  produced  the  result  might  be  a  sen- 
sation unpleasant  from  its  intensity.  This  is  partially  obviated 
by  the  damping  effect  of  the  auditory  ossicles,  which  also  pre- 
vent after-vibrations. 

Soi&e  suppose  that  what  we  denominate  shrill  or  harsh 
sounds  are,  in  part  at  least,  owing  to  the  auditory  meatus  hav- 
ing a  corresponding  fundamental  note  of  its  own. 

The  Auditory  OmIoIin.— Though  these  small  bones  are  con- 
nected by  perfect  joints,  permitting  a  certain  amount  of  play 
upon  one  another,  experiment  has  shown  that  they  vibrate  in 
response  to  the  movements  of  the  drum-head  en  masse  j  though 


447.— SecUon  of  MidttoiT  organ  of  hone  (•ftorOhauraMi).    A,mMtiorri 

t,  ▼Mti6itoT7.k,£,  outllM  of  Mmldrcttlv  ommW;  JT,  oocUm;  If,  i 
■eala  tjnnpMii. 


608 


ANIMAL  PHYSIOLOGY. 


the  stapes  has  by  no  means  the  range  of  movement  of  the  han- 
dle of  the  malleus ;  in  other  words,  there  is  loss  in  amplitude, 
but  gain  in  intensity.  A  glance  at  Fig.  448  will  show  that  the 
end  attained  by  this  arrangement  of  membrane  and  bony  levers, 
which  may  be  virtually  reduced  to  one  (as  it  is  in  the  frog,  etc.), 
is  the  transmission  of  the  vibrations  to  thd  membrane  of  the 
fenestra  ovalis,  through  the  stcpes  finally,  and  so  to  the  fluids 
within  the  internal  ear.    But  it  might  be  supposed  that,  for  the 


rm.  44B.— Diagnmmatic  repreMntatton  fflualntiiur  Auditory  proceMM  (after  BeMinla).  A, 
external  ear;  iB,  mkldle  ear ;  C,  internal  ear;  ^auricle;  >,  external  andltory  meatua ;  8, 
^rmpanum;  4,  membrana  tratiiant;  B,  Biwtartitan  tube;  6,  nuMtoid  ceUe;  10,  foramen 
rotundum;  U,  forameo  onde ;  U,  Tcatibule;  IS.  cochlea;  14,  aoala  tiympani;  15,  aoala 
veatibuli ;  i9,  fleniciroQlar  iTti**fl*t 

X.  B.— The  ear  ia  w>  oompUoalMl  an  onan  that  it  ia  ahnoat  imposrible  to  glTe  a  diaRram- 
matlc  renreaiitaMon  of  it  at  once  miple  and  complete  in  a  angle  llgure.  A  compariaoii 
of  the  whole  aeriea  of  ottia  ia  tbertfore  deriiabie.  It  le  ewental  to  undertand  how  tlie 
end-oivaa  within  the  aoala  media  ia  ■rtmwlatert. 

avoidance  of  i^ocks  and  the  better  adaptation  of  the  apparatrs 
to  its  work,  some  regulative  apparatus,  in  the  form  of  a  nerv- 
ous and  muscular  mechanism,  would  have  been  evolved  in  the 
higher  groups  of  animals.  Such  is  found  in  the  teosor  tym- 
pani,  lazator  tympani,  and  stapedius  muscles,  as  well  as  the 
Eustachian  tube. 

MimdM  of  the  Middle  ler. — ^The  tensor  tympani  regulates  the 
degree  of  tension  of  the  drum-head,  and  hence  its  amplitude  of 
vibration,  having  a  damping  effect,  and  thus  preventing  the  ill 
results  of  very  loud  soimds. 

Ordinarily  this  is,  doubtless,  a  reflex  act,  in  which  the  fifth 


HEARING. 


609 


t  of  the  lian- 
1  amplitude, 
low  that  the 
bony  levers, 
le  frog,  etc.), 
>rane  of  the 
to  the  fluids 
that,  for  the 


ifter  BeMinki).  A, 
iicUtor]r  meatus ;  8, 
odls ;  10,  fanunmi 
TinpMii ;  15,  MMla 

o  glTe  •  diaRrain- 
irc.  A  comMriKMi 
nderaUnd  EowUm 


he  apparatrs 
m  of  a  nerv- 
rolved  in  the 
tevsor  tym- 
I  well  as  the 

regulates  the 
amplitude  of 
anting  the  ill 

ich  the  fifth 


is  usually  the  afferent  nerve  concerned.  It  is  well-known  that, 
when  we  are  aware  that  an  explosion  is  about  to  take  place,  we 
are  not  as  much  affected  by  it,  which  would  seem  to  argue  a 
voluntary  power  of  accommodation ;  but  of  this  we  must  speak 
with  caution. 

According  to  some  authorities  the  laxcUor  tympani  is  not  a 
muscle,  but  a  supporting  ligament  for  the  malleus.  The  stape- 
ditirS,  however,  has  the  important  function  of  regulating  the 
movements  of  the  stapes,  so  that  it  shall  not  be  too  violently 
driven  against  the  membrane  covering  the  fenestra  ovalis. 

The  two  muscles,  stapedius  and  tensor,  suggest  the  accom- 
modative mechanism  of  the  iris.  The  motor  nerve  of  the  sta- 
pedius is  derived  from  the  facial ;  of  the  tensor,  from  the  tri- 
geminus through  the  otic  ganglion. 

The  luUdliiui  Tube.— Manifestly,  if  the  middle  ear  were 
closed  permanently,  its  air  would  gra4ually  be  absorbed.  The 
drum-head  would  be  thrust  in  by  outward  pressure,  and  become 
useless  for  its  vibrating  function.  The  Eustachian  tube,  bj 
communicating  with  the  throat,  keeps  the  external  and  internal 
pressure  of  the  middle  ear  balanced.  Whether  this  canal  is 
permanently  open,  or  only  during  swallowing,  is  as  yet  unde- 
termined. 

One  may  satisfy  himself  that  the  middle  ear  and  pharynx 
communicate,  by  closing  the  nostrils  and  then  distending  the 
upper  air-passages  by  a  forced  expiratory  effort,  when  a  sense 
of  distention  within  the  ears  is  experienced,  owing  to  the  rise 
of  atmospheric  pressure  in  the  tjrmpanum. 

FaUudflfiMd. — Inflammation  of  the  tympanum  may  i-esult  in 
adhesions  of  the  small  bones  to  other  parts  or  to  each  other,  or 
to  occlusion  of  the  Eustachian  tube  from  excess  of  secretion, 
cicatrices,  etc.,  in  consequence  of  which  the  relations  of  atmos- 
pheric pressure  become  altered,  the  membrani  tympani  being 
indrawn,  and  the  whole  series  of  conditions  on  which  the  nor- 
mal transmission  of  vibrations  de|»8nds  disturbed,  with  the 
natural  result,  partial  deafness.  The  hardness  of  hearing  ex- 
perienced during  a  severe  cold  in  the  head  (catarrh,  etc.)  is 
owing  in  great  part  to  the  occlusion  btth^  Eustachian  tube, 
which  may  be  either  partial  or  complete. 

By  filling  one  or  both  of  the  ears  external  to  the  mem- 
brana  tympani  with  cotton-wool,  one  may  satisfy  himself  how 
essential  for  hearing  is  the  vibratory  mechanism,  which  is,  of 
course,  under  such  circumstances  inactive  or  nearly  so;  hence 
the  deafness. 


M),^nniipwmni« 


mmmii'im'm 


610 


ANIMAL  PHYSIOLOGY. 


When  the  middle  ear  is  not  functionally  active,  it  is  still 
possible,  so  long  as  the  auditory  nerve  is  normal,  to  hear 
vibrations  of  a  body  (as  a  tuning-fork)  held  against  the  head ; 
though,  as  would  be  expected,  discrimination  as  to  pitch  is 
very  imperfect. 

Auditory  impulaea  originate  ^  ithin  the  inner  ear — that  is 
to  say,  in  the  vestibule  and  possibly  the  semicircular  canals. 


Fra.  MB.— Diainm  Intended  to  OhMtnte  Uie  pwcww*  of  beariac  (•««■  LandolaV  AO, 
•ztemal  aiMUtorjr  mwitut ;  T,  ^napanio  membnuie :  K,  taaUium :  a,  inciia ;  P.  mlddte 
car:  o,  (eneatra  oralis;  r,  (eneatra  rotund*;  fi,  acala  tymnani:  vt,  aeala  TcatlbuU;  v, 
veaUbule :  8,  aateale :  V,  utricle ;  H,  aemidrottlar  caaab ;  TB,  BuatadUaa  tube.  Lonff 
arroir  iamnltm  line  of  tnction  of  tenaor  ^mpani ;  abort  curved  one  tbat  o<  Stapedius. 

but  especially  in  the  cochlea.  It  is  to  be  remembered  that  the 
whole  of  the  end-organ  concerned  in  hearing  is  bathed  by  endo- 
lymph;  and  that  the  vibrations  of  the  latter  are  originated  by 


F».  460.— Beetkm  tbrouith  one  o(  ttaeooila  U  ootiUfM^imttarOtumrma).  BT,  icala  Qrmpaai ; 
SF,  soala  veaUbuli ;  OC,  oodilear  oanal  (aeala  metUa):  Oo,  organ  of  Oorti ;  R,  mMnbrane 
of  iti<Miirir ;  6,  memliraaa  baeilarle ;  Ito,  lamina  mralia  oawa ;  I,  membraaa  teotoria; 
l,S,rada(tf Oorti;  ne, cochlear nerre with iU gangfon, ge. 


ismmsmamtmtmsgm 


iye,  it  is  still 
mal,  to  hear 
ist  the  head; 
8  to  pitch  is 

r  ear — that  is 
cular  canals. 


ttw  LuidolaV  AO, 
I,  inciia ;  P.  mlddte 

wdUaa  tube,  uxat 
iMtoCSUpedliM. 

ered  that  the 
thedbyendo- 
originated  by 


ST,  Mate  lympml ; 
)orU ;  R,  mMnbnuie 
Mmbnuw  taotorift; 


HEARING. 


611 


corresponding  vibrations  of  the  perilymph,  which  again  is  sent 
into  oscillation  by  the  movements  of  the  stapes  against  the 
membrane  covering  the  fenestra  ovalis ;  so  that  the  vibrations 
thus  set  up  without  the  membranous  labyrinth  are  trans- 
formed into  similar  ones  within  the  vestibule  and  the  scala 
vestibuli,  and  end,  after  passing  over  the  scala  tympani,  against 
the  membrane  of  the  fenestra  rotunda.  The  cochlear  canal 
may  be  regarded  as  the  seat  of  the  most  important  part  of  the 
organ  of  hearing,  and  answers  to  the  macula  lutea  of  the  eye 
in  many  respects. 


"*■  4B1-— !•  Thuwvcne  secUon  of  a  turn  of  oodilea.   IL  Ammilla  of  a  lenileircnlar  canal 
and  tta  orMa  acou^a :  c^au^DProi^  vubtitiMA  ja  a  halroeU.   m.  Diagnun  of 


labyrinth  of 


riUi.   (After Landota.) 


The  organ  of  Corti  has  given  rise  to  certain  speculations 
which  require  a  brief  notice.  It  has  been  supposed  that,  as  the 
key-board  of  a  piano  may  be  said  to  cause  certain  tones  by 
being  associated  with  stretched  wires  of  varjring  lengths,  so 
the  vibrations  of  the  rods  of  Corti  originate  in  certain  nerve- 
fibers  the  sensations  answering  to  the  different  tones  we  hear. 
It  was  found,  however,  (1)  that  these  rod8,'though  very  nu- 
merous (6,000  to  10,000),  are  insufficient  to  account  for  the 
actual  range  of  our  hearing ;  (2)  that  they  are  absent  in  certain 
classes  of  animals  that  discriminate  sounds  very  well,  as  birds ; 
and  (3)  that  the  nerve-fibers  do  not  terminate  in  these  rods  at 
all,  but  in  the  hair-cells  of  the  organ  of  Corti.  It  is  now  pro- 
posed that  the  haaiUir  membrane  (present  in  birds)  may,  like  a 
series  of  tense  strings  of  different  lengths,  be  the  required 
organ.    The  failure  of  certain  theories  of  vision  should  have 


612 


ANIMAL  PHYSIOLOGY. 


KX 


made  physiologists  cautious  in  adopting  so  mechanical  an  expla- 
nation.    If  all  our  perceptions  of  color,  however  minute  the 


Fm.  4Sa.— DtagramnMtle  renmanteMon  of  dnetoa  ooeUeMto  and  otrmw  of  OortI  («fter  Lmi- 
dois).  N,  nerve  of  owaileM ;  JT.  inner,  and  P,  outer,  hair-oells ;  n,  nerre-flbrllii  tennK 
natliig  in  P:  a, a,  mraortinc  oailH ;  d,  cells  of  Miooaa  qiinlie ;  s,  inner  rod  of  Corti :  y, 
outer  rod  of  Oortl :  ow,  membrane  of  Oorti  (membrann  tedoria) ;  o,  membnuia  retlen. 
laria;  H,  O, oella of  nrea toward oat«r wall. 

shade  of  difference  from  others  (and  some  believe  we  can  recog- 
nize millions  of  such  gradations),  are  the  result  of  the  fusion, 


A.N. 


tw.«i 


no.«iS. 


Fio.  ««.— Audltonr  etrftheUum  from  maonla  acooitlca  of  aaomle  of  alligator,  much  macni- 
fled  (after  Schlm).  e,e,  oohimnar  hairoeHa;  /,/,  llberoells;  n,  nerre-flber  kwliis  Ite 
medollanr  iheatli  moA  alMut  to  teoninato  In  oohimnar  auditory  cells :  h,  audttory  nair ; 
V,  base  of  anditorr  hairs  spHt  up  into  fibrils.  _  ^        .      „ 

Fm.  4M.— Diagrammatic  reprMsntatioa  of  distflbatiaB  of  auditoiT 
labgrrtnth  and  oodilea  (after  Huzlejr). 


nenre  in  membrawms 


JBiJiui  iiriTwiBlJMlBJiMK'iiilja'ij'rij-  iiijM.»»!MrRiWiiagriii!ii|-;jiy#ajwil^TOt.»>J>^J„limW«W..^ 


cal  an  expla- 
minute  the 


f  CXxtl  (kfter  Lmi- 
aerre-flbrlki  tennK 
v  rod  of  OorU:  y, 
■Beinbrwift  renen- 


re  can  recog- 
f  the  fusion. 


■tor.  mudi  maeni- 
rre-flber  kwlns  its 
:  k,iH)dltory  Mbr; 

re  in  membraimH 


HEARING. 


618 


etc.,  of  three  different  fundamental  sensations,  or  the  result  of 
chemical  processes  few  in  kind,  why  should  not  hearing  be 
explained  in  an  equally  simple  way  ?    Such  views  as  those  re- 


a.h. 


.,-      B 

Fka.  4BB.— Loagltiidtaal  mcMcmi  of  Miipiills,  loiiiewliat  JlaymwwHe  (jMat  Rwley).  e.  end 
of  Mnpidl*  JolliitriCHiiiieiraiilMroMMl;  «,qmiiliic  into  utricle ;  er,  eriito  MointioA  with 
hair-oelliL  to  whieSmajr  tw  Men  paMoft  «,  Hben  of  Miditofjr  nervs ;  et,  ooBBecttTe-tiHue 
support  fur  Midltaty  hiin. 

ferred  to  above  seem  to  us  utterly  at  variance  with  the  f imda- 
mentAl  conceptions  of  biology ;  are  so  purely  conceptions  that 
have  their  birth  in  physics,  that  we  deem  it  wiser  to  rest  with* 
out  any  attempt  at  an  explanation  of  the  origin  of  auditory 
sensations  in  detail,  than  to  accept  such  curtificial  and  inadequate 
solutions  as  have  been  proposed.  Sv^dive  sensations  of  hear- 
ing' are  common  enough  in  the  insane,  and  answer  to  the  visions 
of  tne  same  clam  of  persons;  so  that  we  must  recognize  the 
possibility  of  such  sensatiqns  arising  without  the  usual  external 
stimulus. 


mmmir 


^ 


614 


ANIMAL  PHYSIOLOGY. 


Fra.  4B6.-IHMrMn  lotMided  to  flluMnrte  nIattTe  portHoB  o(  Tarfaiaa  parti  of^ 

tor).  ^JTeKtanMlMiilttarjiMttiM;  !>.  Jf,  QmiMiilo  iMmbraiw ;  IV.  tTnpMnm ;  Mall, 
-DUkUewi;  Inc.  tow ;  atp,  atopy ;  #.?,  Uufttf  owflto ;  r.  r./wwrtra  rofama* ;.»»,  «u«tod»»- 
an  tube;  Jtf.I^niMnbniioMili^rnatlLaolsroaaof  theaamieininlaroaiiaka^ 
liigwpwaaiitad;ato.r.flDtt.aCftarfc.ai«lwolcochla>.i«pfaaaa>«ilaaatra%lit(Macoaa» 


Ro.  «vr.-I1iatognpWo  diacram  of  lalTriitli  (after  fttnt  and  BOdlnmr).   Vm»  ,fl{!*nw :  1. 
utricle ;  llaaooaS?;  &!MMndicawH» ooeUea ;  4, oualia  reonleiia ;  6.  amtafreular mm^ 


8,  iaeonte:  S,4,S,_amp«dtej  fc^»J».iiMnlcirwilar  canato ;  10. 


auditoiT^Te  (pMtlj^  diu^ammatio)T  Ji.li.  IsTl*.  U^  JUrftuilon  at  tmnebea  of  nerre 
to  Teatlbule  and  r     '  ' 


*3iw:>  -■ '  sitstmiiimm 


|>>illliiMiiii|Min>  I II  ruiiinrTiiriiKiii 


HBARINO. 


616 


of  ••r(«flerHin- 
tympMnim ;  Mall, 
■da;  Ai,liiiaUMdit- 
uid  ita  MBDullab*- 


ITpfwr  tgun :  1, 

MBlofreular  ommIi 

stavolar  canala;  10, 

IxmiiebM  of  nerre 


The  structure  of  the  ampull»  of  the  semicircular  canals, 
and  other  parts  of  the  labyrinth  besides  those  specially  con- 
sidered, with  their  peculiar  hair-cells,  suggests  an  auditory 
function ;  but  what  that  may  be  is  as  yet  quite  undetermined. ' 


Via.  M.— DiitrlfautioBofooddMHriiHTeliiqilnl  Umiiiaaf  Mitcra^iiteter  pwi  of  ooefalM  of 
right  ew  (after  Smcy).  1,  tntak  of  oodilMU-  nerre :  S.  menibmiaiM  aone  of  wftnA 
iMnin*;  S,  termtaMTeKpitaiion  of  ooohlear  nerve  ezpowd  tliraagliout  bj  rHBOval  of  eap^ 
rior  ptete  of  laaia*  •ptraUe ;  4,  orUloe  of  eommnnleation  between  eonla  tympnal  ud 


It  has  been  thought  that  the  parts,  other  than  the  cochlea,  are 
concerned  with  the  appreciation  of  noise,  or  perhaps  the  in- 
tensity of  sounds ;  but  this  is  a  matter  of  pure  speculation. 

AuDiTOBT  Sensations,  Pbbceptions,  and  Judgments. 

We  have  thus  far  been  concerned  with  the  conduction  of 
the  a§rial  vibrations  that  are  the  physical  cause  of  hearing; 
but  before  we  can  claim  to  have  "  heard  "  a  word  in  the  highest 
sense,  certain  prooesaes,  some  of  them  physiological  and  some 
psychical,  take  place,  as  in  the  case  of  vision ;  hence  we  may 
speak  of  the  affection  of  the  ond-organ  or  of  auditory  impulses, 
and  of  the  processes  by  which  these  become,  by  the  mediation 
of  the  brain,  auditory  sensations,  and  when  brought  under  the 
cognizance  of  the  mind  as  auditory  perceptions  and  judg- 
ments. 

Auditory  JnlgiMiita. — Such  are  much  more  frequently  erro- 
neous than  are  our  visual  judgment.s,  whether  the  direction  or 
the  distance  of  the  sound  be  considered.  As  in  the  case  of  the 
eye,  the  muscular  sense,  from  accommodation  of  the  vibratory 
mechanism,  may  assist  our  judgments,  being  aided  by  our 
stored  past  experiences  (memory)  according  to  the  law  of 


616 


ANIMAL  PHYSIOLOGY. 


asfiociation.  Sounds  are,  how  •  j  ,  ai  r.  i»yb  ref erre^l  to  the  world 
without  U8.  The  animals  with  ;:>  r^Mo  -ar'  greatly  excel  man 
in  estimating  the  direction,  it  i^t  vhe  distance,  of  sounds. 
There  are  few  physiological  experiments  rriure  amusing  than 
those  performed  on  a  person  blindfolded,  when  attempting  to 
determine  either  the  distance  or  the  direction  of  a  sounding 
tuning-fork,  so  gross  are  the  errors  made. 

One  who  mfUces  such  observations  on  others  may  notice 
that  most  persons  move  the  ears  slightly  when  attempting  to 
make  the  necessary  discriminations,  which  of  itself  tends  to 
show  how  valuable  mobility  of  these  organs  must  be  to  those 
animals  that  have  it  highly  developed. 

Sang*  of  AwSHbuj  DisBriifaaMw  —If  we  compare  the  range 
of  sense-perception  of  eye  and  ear,  we  And  that  the  latter  is  in 
this  respect  far  superior  to  the  former.  Assuming  that  the 
perception  of  red  is  owing  to  the  influence  of  rays  of  light  with 
four  hundred  and  fifty-six  billions  of  vibrations  per  second  and 
violet  at  the  opposite  end  of  the  spectrum  with  rays  of  six  hun- 
dred and  sixty-seven  billions,  it  will  be  seen  that  the  total  range 
does  not  correspond  with  even  one  octave;  while  the  ear  can 
discriminate  between  tones  answering  on  the  one  hand  to  about 
forty  a§rial  vibrations  per  second  and  on  the  other  to  thirty- 
eight  thousand  or  more,  though  this  latter  is  greater  in  the 
upward  direction  than  most  persons  can  appreciate.  Such  lim- 
its answer  to  at  least  ten  times  that  for  the  eye.  On  the  other 
hand,  a  sense-impression  on  the  organ  of  hearing  lasts  a  shorter 
time  by  far  than  in  the  case  of  the  eye,  so  that  fusion  of  audi- 
tory sense^impressions  is  less  readily  produced. 


\ 


Special  Conbidbbations. 

Oompanttv*. — Among  invertebrates  steps  of  progressive  de- 
velopment can  be  traced.  Thus,  in  certain  of  the  jelly-fishes  we 
find  an  auditory  vesicle  (Fig.  459)  inclosing  fluid  provided  with 
one  or  more  otoliths  or  calcareous  nodules  and  auditory  cells 
with  attached  cilia,  the  whole  making  up  an  end-organ  connected 
with  the  auditory  nerve.  A  not  very  dissimilar  arrangement 
of  parts  exists  in  certain  moUusks  (Fig.  460).  The  vesicle  may 
lie  on  a  ganglion  of  the  central  nervous  system.  On  the  other 
hand,  the  vesicle  may  lie  open  to  the  exterior,  as  in  decapod 
crustaceans;  and  the  otoliths  be  replaced  by  grains  of  sand 
from  without.  It  is  difficult  to  decide  what  the  function  of 
otoliths  may  be  in  mammals ;  but  there  seems  to  be  little  reason 


■  'juJi  jwuWji»MiWivJ-wiiiM-wiit.t<ki»wJ»jww*iit»t'»'*wy.'j*w».i^ 


HEARIMO. 


617 


to  the  world 
ly  excel  man 
I,  of  sounds, 
musing  than 
ttempting  to 
I  a  sounding 

I  may  notice 
attempting  to 
self  tends  to 
t  be  to  those 

ire  the  range 
he  latter  is  in 
ling  that  the 
of  light  with 
er  second  and 
ys  of  six  hun- 
be  total  range 
e  the  ear  can 
hand  to  about 
ther  to  thirty- 
plater  in  the 
be.    Such  lim- 
6n  the  other 
lasts  a  shorter 
usion  of  audi- 


)rogressive  de- 
jelly-fishes  we 
provided  with 
auditory  cells 
rgan  connected 
p  arrangement 
he  vesicle  may 
On  the  other 
as  in  decapod 
ptdns  of  sand 
he  function  of 
be  little  reason 


to  doubt  that  they  communicate  vibrations  in  the  invertebrates. 
When  the  cephalopod  mollu.sks,  with  their  highly  developed 
nervous  system,  are  reached,  we  find  a 
membranous  and  cartilaginous  laby- 
rinth. 

Among  vertebrates  the  different  parts 
of  the  mammalian  ear  are  found  in  all 
staged  of  development.  The  outer  ear 
may  be  wholly  wanting,  as  in  the  frog, 
or  it  may  exist  as  a  meatus  only,  as  in 
birds.  The  tympanic  cavity  is  wanting 
in  snakes.  Most  fishes  have  a  utricle 
and  three  semicircular  canals,  but  some 
have  only  one ;  and  the  lowest  of  this 
group  have  an  ear  not  greatly  removed 
from  the  invertebrate  type,  as  may  be 
seen  in  the  lamprey,  which  has  a  saccule 
with  auditory  hairs  and  otoliths,  in  com- 
munication with  two  semicircular  ca- 
nal&  Most  of  the  amphibia  are  without 
a  membrana  tympani.  The  frog  has  (1) 
a  membrana  tympani  communicating  with  the  inner  ear  by  (2) 
a  bony  and  cartilaginous  lever  {(xHumeUa  auris),  and  (3)  an 
inner  ear  consisting  of  three  semicircular  canals,  a  saccule  and 


Flo.  4W.  — Auditory  TMtcle  of 
0«ryoftte  (Carmarina),  teen 
from  Um  Rirfaoe  (After  O. 
ud  a  Hcitwig).  ymadN', 
tile  uMtorj  nerves ;  Ot,  oto- 
Uth :  Hm,  MxUtorv  cells;  H*. 
•iiditary  ciU*  (type  at  the 
MidltoiT  organ  of  the  Tra- 
ckym»au$at). 


FM.  4M.  — Auditorr  vesiole  of  a  heteropod  moUusk  {Pterottnvhea)  (after  Clans).  N,  auditory 
nerve ;  Ot,  otolith  In  fluid  of  vesicle ;  H'Jt,  ciliated  cells  on  inner  wall  of  vesicle ;  Bm,  audt 
tofy  cells ;  Cz,  central  cells. 


618 


ANIMAL  PHYSIOLOGY. 


utricle  containing  many  otoliths,  and  a  small  dilatation  of  the 
vestibule,  which  may  indicate  an  undeveloped  cochlea.    The 


l.A 


Via.  Ml.— Otcdttha  firam  wioui  aaliiwlri  (after  Radinger).     1,  from  ipHtt ;  9.  herring ;  8, 
devtt-flah ;  4,  maekerel ;  S,  flying-fleh ;  S,  pike ;  7,  oup ;  8,  ray ;  9,  shark ;  10,  groiMe. 

membranous  labyrinth  is  contained  in  a  periotic  capsule,  partly 
bony  and  partly  cartilaginous,  which  is  supplied  with  per- 
ilymph. There  is  a  fenestra  ovalis,  but  not  a  fenestra  rotunda, 
though  the  latter  is  present  in  reptiles.  In  crocodiles  and 
birds  the  cochlea  is  tubular,  straight,  and  divided  into  a  scala 
tympani  and  a  scala  vestibuli.  The  columella  of  lower  forms 
still  persists.  In  birds  and  mammals  the  bone  back  of  the  ear 
is  hollowed  out  to  some  extent  and  communicates  with  the 
tympanum.  Except  among  the  very  lowest  mammals  (Echid- 
na), the  ear  is  such  as  has  been  described  in  detail  already. 

Broliitioa. — The  above  brief  description  of  the  auditory  organ 
in  different  groups  of  the  animal  kingdom  will  suffice  to  show 
that  there  has  been  a  progressive  development  or  increasing 
differentiation  of  structure,  while  the  facts  of  physiology  point 
to  a  corresponding  progress  in  function — in  other  words,  there 
has  been  an  evolution.  No  doubt  natural  selection  has  played 
a  great  part.  It  has  been  suggested  that  this  is  illustrated  by 
cats,  that  can  hear  the  high  tones  produced  by  mice,  which 
would  be  inaudible  to  most  mammals;  and,  as  the  very  exist- 
ence of  such  animals  must  depend  on  their  detecting  their  prey, 
it  is  possible  to  understand  how  this  principle  has  operated  to 
determine  even  what  cats  shall  survive.    The  author  has  noticed 


■  r--'— — IMflilni  II 


HBARINO. 


619 


iation  of  the 
ochlea.    The 


jfA ;  S.  hening ;  8, 
rk ;  10,  grouM. 

apsule,  partly 
ed  with  per- 
istra  rotunda, 
pocodUes  and 
d  into  a  scala 
f  lower  forms 
ick  of  the  ear 
btes  with  the 
imals  {Echid- 
[  already, 
uditory  organ 
uffice  to  show 
or  increasing 
rsiology  point 
p  words,  there 
mhas  played 
illustrated  by 
f  mice,  which 
he  Very  exist- 
ng  their  prey, 
as  operated  to 
or  has  noticed 


that  terrier  dogs  also  have  a  very  acute  sense  of  hearing,'  and 
they  also  kill  rats,  etc.  But,  unless  it  be  denied  that  the  im- 
provement from  use  and  the  reverse  can  be  inherited,  this  fac- 
tor must  also  be  taken  into  the  account. 

There  seem  to  be  great  differences  between  hearing  as  it 
exists  in  man  and  in  lower  forms.  Birds,  and  at  least  some 
horses,  possibly  some  cats  and  dogs,  like  music,  and  give  evi- 
dence of  the  possession  of  a  sense  of  rhythm,  as  evidenced  by 
the  conduct  of  the  steed  of  the  soldier.  On  the  other  hand, 
some  dogs  seem  to  greatly  dislike  music.    Certain  animals  that 


gMgUmt;  O'.termiiua portion oCauditoiT nam. 


appear  to  be  devoid  of  true  hearing,  as  spiders,  are  neverthe- 
less sensitive  to  aSrial  vibrations ;  whether  by  some  special  un- 
discovered organ  or  through  the  general  cutaneous  or  other  kind 
of  sensibility  is  unknown.  It  also  seems  to  be  more  than  prob- 
able that  some  groups  of  insects  can  hear  sounds  quite  inaudible 
to  us,  though  by  what  organs  is  in  great  measure  unknown. 

The  so-called  musical  ear  differs  from  the  non-musical  in 
the  ability  to  discriminate  differences  in  pitch  rather  than  in 
quality ;  in  fact,  that  one  defective  in  the  former  power  may 
possess  the  latter  in  a  high  degree  is  a  fact  that  has  been  some- 
what lost  sight  of,  both  theoretically  and  practically.  It  does 
not  at  all  follow  that  one  with  little  capacity  for  tune  may  not 


-. :  r-m0ri>iffi^«>f^ii>ii>si&lll^^:s^-^ 


620 


ANIMAL  PHYSIOLOGY. 


have  the  qualifications  of  ear  requisite  to  make  a  first-rate  elo- 
cutionist. Following  custom,  we  have  spoken  as  though  cer- 
tain defects  and  their  opposites  depended  on  the  ear,  but  in 
reality  we  can  not,  in  the  case  of  man  at  all  events,  afi&rm  that 
such  is  the  case;  indeed,  it  seems,  on  the  whole,  more  likely 
that  they  are  cerebral  or  mental.  Auditory  discriminations 
seem  to  be  equally  if  not  more  susceptible  of  improvement  by 
culture  than  visual  ones,  especially  in  the  case  of  the  young. 

A  "good  ear"  seems  to  depend  in  no  small  degree  on  mem- 
ory of  sounds,  though  the  latter  may  again  have  its  basis  in  the 
auditory  end-organs  or  in  the  cerebral  cortex,  as  concerned  in 
hearing.  The  necessity  for  the  close  connection  between  the 
co-ordinations  of  the  laryngeal  apparatus  in  singing  and  speak- 
ing and  the  ear  might  be  inferred  from  the  fact  that  many  ex- 
cellent musicians  are  themselves  unable  to  vocalize  the  music 
they  perfectly  appreciate. 

Synopiii  of  the  Phyiiology  of  Eouiag.— The  ear  can  appreciate 
differences  in  pitch,  loudness,  and  quality  of  sounds,  though 
whether  different  parts  of  the  inner  ear  are  concerned  in  these 
discriminations  is  tmknown.  Hearing  is  the  result  of  a  series 
of  processes,  having  their  physical  counterpart  in  aerial  vibra- 
tions, which  begin  in  the  end-organ  in  the  labyrinth  and  ter- 
minate in  the  cerebral  cortex.  We  recognize  conducting  ap- 
paratus which  is  membranous,  bony,  and  fluid.  The  auditory 
nerve  conveys  the  auditory  impulses  to  the  brain,  though  ex- 
actly what  terminal  cells  are  concerned  and  how  in  originating 
them  must  be  regarded  as  undetermined.  The  essential  part  of 
the  organ  of  hearing  is  bathed  by  endolymph,  and  the  princi- 
pal part  (in  mammals)  is  within  the  cochlear  canal.  Man's 
power  to  locate  sounds  is  very  imperfect.  The  auditory  brain 
center  (or  centers)  has  not  been  definitely  located.  Compara- 
tive anatomy  and  physiology  point  clearly  to  a  progressive 
development  of  the  sense  of  hearing. 


THE  SENSE  OF  8MELL. 

The  nose  internally  may  be  divided  into  a  respiratory  and 
an  olfactory  region.  The  latter,  which  corresponds,  of  course, 
with  the  distribution  of  the  olfactory  nei  ve,  embraces  the  upper 
and  part  of  the  middle  turbinated  bone  and  the  upper  part  of 
the  septum,  all  of  which  differ  in  microscopic  structure  from 
the  respiratory  region.    Among  the  ordinary  cylindrical  epi- 


iWMiwi;iiif,«ii,» 


■HP)Wrr).ii;i,i|j   mj.j 


THE  SBNSB-  OF  SMELL. 


^21 


first-rate  elo- 
i  though  cer- 
e  ear,  but  iu 
IS,  afi&rm  that 
,  more  likely 
scriminations 
jrovement  by 
the  young, 
gree  ou  mem- 
s  basis  in  the 
concerned  in 
between  the 
Qg  and  speak- 
hat  many  ex- 
ize  the  music 

»n  appreciate 
unds,  though 
)med  in  these 
lilt  of  a  series 
I  aerial  vibra- 
:inth  and  ter- 
mducting  ap- 
The  auditory 
n,  though  ex- 
in  originating 
jential  part  of 
ad  the  princi- 
canal.  Man's 
-uditory  brain 
d.  Compara- 
a  progressive 


)spiratory  and 
ids,  of  course, 
aces  the  upper 
upper  part  of 
tructure  from 
^lindrical  epi- 


thelium of  the  olfactory  region  are  found  peculiar  hair-cells 
highly  suggestive  of  those  of  the  labyrinth  of  the  ear,  and 


Fio.  468.-Parto  concerned  to  (mwll  (•fter  HincMrid).    1.  ^««Sonrj^U«i  and  nerree ;  «, 
r  IB.  wo.    i-mi*  ™^  ^  ^^^^^^  ^^^^  dtatributed  over  Ute  turbtoaled  bones. 

which  are  to  be  regarded  as  the  end-organs  of  smell.    If  aro- 
matic bodies  be  held  before  the  nose,  and  respiration  suspended, 
they  will  not  be  recognized  as  such, 
and  it  is  well  known  that  sniffing 
greatly  assists  the   sense  of    smell. 
Again,  if  fluids,  such  as  eau  de  Co- 
logne, be  held  in  the  nose,  their  aroma 
is  not  detected ;  and  immediately  after 
water  has  been  kept  in  the  nostrils 
for  a  few  seconds,  it  may  be  noticed 
that  smell  is  greatly  blunted.    Such 
is  the  case  also  when   the   mucous 
membrane  is  much  swollen  from  a 
cold.    There  can  be  no  doubt  that  the 
presence  of  fluid  in  the  above  cases  is 
injurious  to  the  delicate  hair-cells, 
and  that  smell  is  dependent  upon  the 
excitation  of  those  cells  by  extremely 
minv/e  particles  emanating  from  aro- 
matic bodies. 

When  ammonia-  is  held  before  the 
nose,  a  powerful  sensation  is  experi- 
enced ;  but  this  is  not  smell  proper,  but  an  affection  of  ordi- 
nary sensation,  Owing  to  stimulation  of  the  terminals  of  the 


622 


ANIMAL  PHYSIOLOGY. 


fifth  nerve.  It  is  possible  that  the  auditory  nerve  may  also 
participate,  though  certainly  not  so  as  to  produce  a  pure  sen- 
sation of  smell. 

Like  the  other  sense-organs,  that  of  smell  is  readily  fa- 
tigued ;  and  perhaps  the  satisfaction  from  smelling  a  bouquet 
of  mixed  flowers  is  comparable  to  viewing  the  same,  one  scent 
after  another  being  perceived,  and  no  one  remaining  predomi- 
nant. 

Our  judgment  of  the  position  of  bodies  possessing  smell  is 
less  perfect  even  than  for  those  emitting  sounds ;  but  we  always 
project  our  sensations  into  the  outer  world,  never  referring  the 
object  to  the  nose  itself.  Subjective  sensations  of  smell  are 
rare  in  the  normal  subject,  though  common  enough  among  the 
diseased,  as  is  complete  or  partial  loss  of  smell.  It  has  been 
found  that  injury  to  the  fifth  nerve  interferes  with  smell,  which 
is  probably  due  to  trophic  changes  in  the  olfactory  region. 

Oompamtive. — The  investigation  of  the  senses  in  the  lower 
forms  of  life  is  extremely  difficult,  an4  in  the  lowest  presents 
almost  insurmountable  obstacles  to  the  physiologist,  because 
their  psychic  life  is  so  far  removed  from  our  own  in  terms  of 
which  we  must  interpret,  if  at  all. 

The  earliest  form  of  olfactory  organ  appears  to  be  a  depres- 
sion lined  with  speqial  cells  in  connection  with  a  nerve,  which, 
indeed,  suggests  the  embryonic  beginnings  of  the  olfactory 
organ  in  vertebrates,  as  an  involution  (pit)  on  the  epithelium  of 
the  head  region.  It  would  appear  that  we  must  believe  that  in 
some  of  the  lower  forme  of  invertebrates  the  senses  of  smell 
and  taste  are  blended,  or  possibly  that  a  perception  results 
which  is  totally  different  from  anything  known  to  us.  The 
close  relation  of  smell  and  taste,  even  in  man,  will  be  referred  to 
presently.  There  are,  perhaps,  greater  individual  differences  in 
sensitiveness  of  the  nasal  organ  among  mankind  than  of  any 
other  of  the  sense-organs.  Women  usually  have  a  much  keener 
perception  of  odors  than  men.  The  sense  of  smell  in  the  dog 
is  well  known  to  b: .  of  extraordinary  acuteness ;  but  there  are 
not  only  great  differences  among  the  various  breeds  of  dogs, 
but  among  individuals  of  the  same  breeds ;  and  this  sense  is 
being  CQnstantly  improved  by  a  process  of  "  artificial  selection  " 
on  the  part  of  m-in,  owing  to  the  institution  of  field  trials  for 
setters  and  pointers,  the  best  dogs  for  hunting  (largely  deter- 
mined by  the  sense  of  smell)  being  us«d  to  breed  from,  to  tho 
exclusion  of  the  inferior  in  great  part.  '  ar  own  power  to 
think  in  teims  of  smell  is  very  feeble,  and  in  this  respecti  the 


^a6(WisaBS'!^.««w.«3*j«fs?v.. 


THE  SENSE  OF  TASTE. 


628 


ye  may  also 
B  a  pure  sen- 

I  readily  fa- 
ig  a  bouquet 
ae,  one  scent 
ng  predomi- 

3ing  smell  is 
at  we  always 
referring  the 
of  smell  are 
ti  among  the 
It  has  been 
smell,  which 
■  region, 
in  the  lower 
rest  presents 
^st,  because 
I  in  terms  of 

be  a  depres- 
lerve,  which, 
be  olfactory 
pithelium  of 
(lieve  that  in 
ises  of  smell 
3tion  results 
to  us.  The 
le  referred  to 
lifferences  in 
than  of  any 
much  keener 
1  in  the  dog 
mt  there  are 
leda  of  dogs, 
this  sense  is 
al  selection" 
Bid  trials  for 
argely  deter- 
from,  to  tho 
vn  power  to 
B  respect  the 


dog  and  kindred  animals  probably  have  a  world  of  their  own 
to  no  small  extent.  Their  memory  of  smells  is  also  immeasur- 
ably better  than  our  own.  A  dog  has  been  known  to  detect  an 
old  hat,  the  property  of  his  master,  that  had  been  given  away 
two  years  before',  as  evidenced  by  his  recoveiing  it  from  a 
remote  place. 

The  importance  of  smell  as  a  guide  in  the  selection  of  food, 
in  detecting  the  presence  of  prey  or  of  enemies,  etc.,  is  very 
obvious.  By  culture  some  persons  have  learned  to  distinguish 
individuals  by  smell  alone,  like  the  dog,  though  to  a  less  degree. 


THE  SENSE  OP  TASTE. 

The  tongue  is  provided  with  peculiar  modifications  of  epi- 
thelial cells,  etc.,  known  as  papillee  and  taste-buds  which  may 
be  regarded  as  the  end-organs  of  the  glosso-pharyngeal  and 
lingual  nerves ;  though  that  these  all,  especially  the  taste-buds, 
are  concerned  with  taste  alone,  seems  more  than  doubtful.  In 
certain  animals  with  rough  tongues,  the  papilla,  certain  of 
them  at  least,  answer  to  the  hairs  of  a  brush  for  the  cleansing 
and  general  preservation  of  the  coat  of  the  animal  in  good  con- 
dition. We  may,  perhaps,  speak  of  certain  fundamental  taste- 
perceptions,  such  as  sweet,  bitter,  acid,  and  saline.  Certainly 
the  natural  power  of  gustatory  discrimination  is  considerable ; 
ami,  as  in  the  case  of  tea-tasters,  capable  of  extraordinary  culti- 
vation. All  parts  of  the  tongue  are  not  equally  sensitive,  nor 
is  taste-sensation  confined  entirely  to  the  tongue.  It  can  be 
shown  that  the  back  edges  and  tip  of  the  tongue,  the  soft  palate, 
the  anterior  pillars  of  the  fauces,  and  a  limited  portion  of  the 
back  part  of  the  hard  palate,  are  concerned  in  tasting.  Making 
allowances  for  individual  differences,  it  may  be  said  that  the 
biick  of  the  tf)ngue  appreciates  best  bitter  substances,  the  tip, 
sweet  ones,  and  tho  edgea  acids. 

If  any  subst^ace  with  a  decided  taste  be  placed  upon  the 
tongue  when  wiped  quite  dry,  it  can  not  be  tasted  at  all,  show- 
ing that  solutior.  is  essential. 

If  a  piece  of  apple,  another  of  potato,  and  a  third  of  onion, 
be  placed  upon  the  tongue  of  a  person  blindfolded,  and  with 
the  nostrils  closed,  he  will  not  be  able  to  distinguish  them, 
showing  that  the  senses  of  smell  and  of  taste  are  related ;  or, 
perhaps,  it  may  be  said  that  much  that  we  call  tasting  is  in 
large  part  smelling.    When  the  electrodes  from  a  battery  are 


ii^^Wf'    :    -^l^iJfHtHftPill 


■Wiiiii'iiM 


624 


ANIMAL  PHYSlOLOOr. 


.  placed  on  the  tongue,  a  sensation  of  taste  is  aroused,  described 
differently  by  diflEerent  persons ;  also  when  the  tongue  is  quick- 


Fia.  «I6.— Pmllbe  of  tmigue  (After  Sappejr).    1,  dnmmTallate  p^rilte ;  8.  fungifOm  p*|iilla» ; 
4,  flUform  papiUaB ;  S,  gunds  at  baae  of  tongue ;  7,  tonalla. 

ly  tapped,  she  ying  that,  though  taste  is  usually  the  result  of 
chemical  stimulation,  it  may  be  excited  by  such  as  are  electrical 
or  mechanical. 

But  it  is  not  to  be  forgotten  that  we  have  usually  no  pure 
jt\;'.tatory  sensations,  but  that  these  are  necessarily  blended 
with  thofc '  of  common  sensation,  temperature,  etc.,  and  that  our 
judgments  \yaBst,  in  the  nature  of  the  case,  be  based  upon  highly 
complex  data,  even  leaving  out  of  account  other  senses  such  as 
vision. 


ised,  described 
mg^e  is  quick- 


8,  fungiform  p*pill«» ; 


ly  the  result  of 
as  are  electrical 

usually  no  pure 
ssarily  blended 
■jO.,  and  that  our 
3ed  upon  highly 
r  senses  such  as 


THE  SENSE  OP  TASTE. 


^25 


The  glosso-pharyngeal  is  the  principal  nerve  for  the  back  of 
the  tongue,  and  for  the  tip,  the  lingual ;  or  according  to  some 
special  fibers  in  this  nerve,  derived  from  thp  chorda  tympani. 


Vto.  4M. 


Fro.  407. 


Flo.  48S.— Ifodtum-riMd  oircumTallate  pHiUto  <f  fter  8*ppey). 

Fio.  487.— Vsriom  Uiids  of  iMq>ilUB  (after  Sa^pey).    1,  fungiform ;  S,  8, 4,  S,  6,  flUform ;  7, 
hemlqAerical  paiiilte. 

It  is  worthy  of  note  that  temperature  has  much  to  do  with 
gustatory  sensations,  a  very  low  or  a  very  high  temperature 
being  fatal  to  nice  discrimihation,  and,  las  would  be  expected,  a 


7^a.  468.— Tfl«te-buda,  from  tongue  of  rabbit  (after  Engelmanii). 

temperature  not  far  removed  from  "  body-hoat "  (40'  C.)  is  the 
most  suitable. 

A  certain  amount  of  pressure  is  favorable  to  tasting,  as  any 
one  may  easily  determine  by  simply  allowing  some  solution  of 
quinine  to  rest  on  the  tongue,  and  comparing  the  sensation  with 
that  resulting  when  the  same  is  rubbed  into  the  organ ;  hence 
the  importance  of  the  movements  of  the  tongue  in  appreciating 
the  sapid  qiiM^ities  of  food. 

PttiioUflMil.  —  Among  insane   persons    both  olfactory  and 

40 


ANIMAL  PHYSIOLOGY. 


gustatory  subjective  sensations  are  common,  and  must  be  re- 
ferred to  the  central  nervous  system. 

After  the  injection  of  some  drugs  subcutaneously,  certain 
tastes  are  expeidenced.  Persons  born  deficient  in  the  sense  of 
smell  to  a  marked  degree  are  very  frequently  also  wanting  in 
tasting  power. 

OaiiipanitiT«.-7-Among  the  lowest  forms  of  life  it  is  extremely 
diflBcult  to  determine  to  what  extent  taste  and  smell  exist  sepa- 
rately or  at  all,  as  we  can  conceive  of  them.  The  differentia- 
tion between  ordinary  tactile  sensibility  and  these  senses  has 
no  doubt  been  very  gradually  effected.  Observations  on  our 
domestic  animals  show  that  their  power  of  discrimination  by 
taste  as  well  as  by  smell  is  very  pronounced,  though  their  likes 
and  dislikes  are  so  different  from  our  own  in  many  instances. 
At  the  same  time  we  find  that  they  often  coincide,  and  it  is  not 
unlikely  that  a  dog's  power  of  discriminating  between  a  good 
beefsteak  and  a  poor  one  is  quite  equal  if  not  superior  to  man's, 
and  certainly  so  if  his  sense  of  taste,  as  in  the  human  subject, 
is  developed  in  proportion  to  his  smelling  power. 


THE  CBREBRO-SPINAL  SYSTEM  OP  NERVES. 

I.  Spinal  Nerves. 

These  (thirty-one  pairs),  which  leave  the  spinal  cord  through 
the  intervertebral  foramina,  are  mixed  nerves — ^i.  e.,  their  main 
trunks  consist  of  motor  and  sensory  fibers.  But  before  they 
enter  the  spinal  cord  they  separate  into  two  groups,  which  are 


Flo.  4«.— DlMtnin  of  raoto  of  nliial  nerre  OhMtratliig  effects  of  KcUon  (utter  Daltoa).   The 
<Uri(  regtoM  tndioate  «be  degMMimted  parta. 

known  as  the  anterior  or  motor  and  the  posterior  or  sensory 
roots,  which  make  connection  with  the  anterior  and  posterior 
gray  horns  respectively. 


THE  CEREBROSPINAL  SYSTEM  OF  NERVES. 


627 


1  must  be  re- 

ously,  oertftin 
1  the  sense  of 
so  wanting  in 

it  is  extremely 
lell  exist  sepa- 
le  differentia- 
)se  senses  has 
ations  on  our 
rimination  by 
igh  their  likes 
any  instances. 
»,  and  it  is  not 
etween  a  good 
erior  to  man's, 
uman  subject. 


KVES. 


1  cord  through 
,  e.,  their  main 
it  before  they 
aps,  which  are 


n  (•{!»  Dalton).   The 

rior  or  sensory 
and  posterior 


These  facts  have  been  established  by  a  few  simple  but  im- 
portant physiological  experiments,  which  will  now  be  briefly 
described:  1.  Stimulation  of  the  peripheral  end  of  a  spinal 
nerve  g^ves  rise  to  muscular  movements ;  while  stimulation  of 
its  central  end  causes  pain.  2.  Upon  section  of  the  anterior 
root,  stimulation  of  its  central  end  gives  negative  results ;  but 
of  its  peripheral  end  causes  muscular  movements.  3.  After 
section  of  the  posterior  root,  stimulation  of  the  distal  end  is 
followed  by  no  sensory  or  motor  effects ;  of  its  central  end,  by 
sensory  effects  (pain). 

These  experiments  show  clearly  that  the  anterior  roots  are 
motor,  the  posterior  sensory,  and  the  main  trunk  of  the  nerve 
made  up  of  mixed  motor  and  sensory  fibers. 

SsoeptioiL — It  has  been  found  that  sometimes  stimulation  of 
the  peripheral  end  of  the  anterior  root  has  given  rise  to  pain, 
an  effect  which  disappears  if  the  posterior  root  be  cut.  From 
this  it  is  inferred  that  certain  sensory  fibers  turn  up  into  the 
anterior  root  a  certain  distance.  Such  are  termed  "  recurrent 
sensory  fibers." 

Additional  BzperiiiMnti.— 1.  It  is  found  that  if  the  anterior 
root  be  cut,  the  fibers  below  the  point  of  section  degenerate, 
while  those  above  it  do  not.  8.  On  the  other  hand,  when  the 
posterior  root  is  divided  above  the  ganglion,  the  fibers  toward 
the  cord  degenerate,  while  those  on  either  side  of  the  ganglion 
do  not.  From  these  experiments  it  is  inferred  that  the  cells  of 
the  posterior  ganglion  are  essential  to  the  nutrition  of  the  sen- 
sory fibers,  and  those  of  the  anterior  horn  of  the  cord  to  the 
motor  fibers. 

PaihokcioaL— Pathology  teaches  the  same  lesson,  for  it  is 
observed  that,  when  there  is  disease  of  the  anterior  gray 
comua,  degeneration  of  motor  fibers  is  almost  sure  to  follow. 
These  cells,  whether  in  the  ganglion  or  the  anterior  horn,  have 
been  termed  "  trophic."  It  is  true,  the  functions  of  the  ganglia 
on  the  posterior  roots,  other  than  those  just  indicated,  are  un- 
known ;  on  the  other  hand,  the  cells  of  the  interior  horn  are 
distinctly  motor  in  function.  To  assume,  then,  that  the  cells 
of  the  ganglion  are  exclusively  trophic,  with  the  evidence  now 
before  us,  would  be  premature. 

The  view  we  have  presented  of  the  relation  of  the  nervous 
system  makes  all  cells  trophic  in  a  certain  sense;  and  we  think 
the  view  that  certain  cells  or  certain  fibers  are  exclusively  tro^ 
phic  must,  as  yet,  be  regarded  as  an  open  question. 

It  is  important,  however,  to  recognize  that  certain  conneo* 


maKMSSsaama 


MRlWa 


m 


628 


ANIMAL  PHYSIOLOGY, 


-tions  between  the  parts  of  the  nervous  system,  and  indeed  all 
of  the  tissues,  are  essential  for  perfect "  nutrition,"  if  we  are  to 
continue  the  use  of  that  term  at  all. 


II.  The  Cranial  Nbrvbs. 

These  nerves  have  been  divided  into  nerves  of  special  sense, 
motor,  and  mixed  nerves. 

The  first  class  has  already  been  considered  with  the  senses 
to  which  they  belong. 

The  physiology  of  the  cranial  nerves  has  been  worked  out 
by  means  of  sections  and  clinico-pathological  investigations. 
Speaking  generally,  a  good  knowledge  of  the  anatomy  of  these 
nerves  is  a  great  step  toward  the  mastery  of  what  is  known 
of  their  functions,  and  such  will  be  assumed  in  this  chapter,  so 
that  the  student  may  expect  to  find  the  treatment  of  the  sub- 
ject somewhat  condensed. 


CoHorlmm 

»nu*itm  «ai|/MMHnMi  tmtieum 
BnuUuMemfwMimm 


Cm* 


jXattMna 
Aecemorhunuelnu 


rtmietitui  euntatut 
ru»leul>u  gracttU 


Fio.  47ft,-Iiit«ided  to  show  Mpedally  the  arigiB  both  deop  and  mperflol*!  of  cnaM  Btrrej 
(•f  ter  T^andoia).  Roman  charactera  are  need  to  Indicate  the  nenrea  aa  they  emerge,  ana 
Arabic  flgurea  their  nuclei  or  deep  origin. 

The  Motor-Oenli  or  Third-  Herre.— With  a  deep  origin  in  the 
gray  matter  of  the  floor  and  roof  of  the  aqueduct  of  Sylvius, 


and  indeed  all 
,"  if  we  are  to 


special  sense, 

ith  the  senses 

an  worked  out 
investigations, 
itomy  of  these 
hat  is  known 
his  chapter,  so 
at  of  the  sub- 


oitfuntUtmm  Mtieum 


tMIHn        \ 

ttduUaml 


Cnw 


lolal  of  cnuiial  nervw 
•  M  tbey  emerge,  and 


ip  origin  in  the 
luct  of  Sylvius, 


THE  CEREBRO-SPINAL  SYSTEM  OP  NERVES. 


699 


branches  of  distribution  pass  to  the  following  muscles :  1.  All 
of  the  muscles  attached  to  the  eyeball,  with  exception  of  the 
external  rectus  and  the  superior  oblique.  2.  The  levator  pal< 
pebree.  3.  The  circular  muscle  of  the  iris.  4.  The  ciliary 
muscle.  Both  the  latter  branches  reach  the  muscles  by  the 
ciliary  nerves,  as  they  pass  from  the  lenticular  (ciliary,  ophthal- 
mic) ganglion.  The  relation  of  the  third  nerve,  as  seen  in  the 
changes  of  the  pupil  with  the  movements  of  the  eyeballs,  has 
already  been  noticed. 

Paihological. — It  follows  that  section  or  lesion  of  the  third 
nerve  must  give  rise  to  the  following  symptoms :  1.  Drooping 
of  the  upper  lid  (ptosis).  2.  Fixed  position  of  the  eye  in  the 
outer  angle  of  the  orbit  (luscitas).  3.  Immobility,  with  dilata- 
tion of  the  pupil  (mydriasis).    4.  Loss  of  accommodation. 

The  TroehlMT  or  Fourth  V«rv«.— This  nerve,  arising  in  the 
aqueduct  of  Sylvius,  pas^f^s  to  the  superior  oblique  muscle. 

Pathological. — Lesi  this  nerve  leads  to  peculiar  chang'es. 

As  there  is  double  visiv...,  some  alteration  must  have  occurred 
in  the  usual  position  of  the  globe  of  the  eye,  though  this  is 
not  easily  seen  on  looking  at  a  subject  thus  affected.  The 
double  image  appears  when  the  eyes  are  directed  downward, 
and  appears  oblique  and  lower  than  that  seen  by  the  unaffected 
eye. 

Tho  Abdvetor  or  fUzth  Vorro. — Arising  on  the  floor  of  the 
fourth  ventricle,  it  passes  to  the  external  rectus  of  the  eyeball, 
thus  with  the  third  and  fourth  nerve  completing  the  innerva- 
tion of  the  external  ocular  muscles  (extrinsic  muscles). 

Pathological. — Lesion  of  this  nerve  causes  paralysis  of  the 
above-mentioned  muscle,  and  consiequently  internal  squint 
(strabismus). 

The  Faeial,  Portia  Dora,  or  Borenfk  Ser?*.— It  arises  in  a  gray 
nucleus  in  the  floor  of  the  fourth  ventricle,  and  has  an  extensive 
distribution  to  the  muscles  of  the  face,  and  may  be  regarded, 
in  fact,  as  the  nerve  of  the  facial  muscles,  since  it  supplies, 
(1)  the  muscles  of  expression,  as  those  of  the  forehead,  eyelids, 
nose,  cheek,  mouth,  chin,  outer  ear,  etc.,  and  (2)  certain  muscles 
ofmasticalion,  as  the  buccinator,  posterior  belly  of  the  digastric, 
the  stylohyoid,  and  also  (3)  to  the  stapedius,  with  branches  to 
the  soft  palate  and  uvula. 

Paihdogical.— It  follows  that  paralysis  of  this  nerve  must 
give  rise  to  marked  facial  distortion,  loss  of  expression,  and 
flattening  of  the  features,  as  well  as  possibly  some  deficiency 
in  hearing,  smelling,  and  swallowing.    Mastioftticm  is  difBcult, 


•• 


680 


ANIMAI    ?HTSIOLOOT. 


and  the  food  not  readily  retained  in  the  mouth.    Speech  is 
affected  £rom  paralysis  of  the  lips,  etc. 

Secretory  fibers  proceed  (1)  to  the  parotid  gland  by  the  super- 
ficial petrosal  nerve,  thence  (2)  to  the  otic  ganglion,  from  which 
the  fibers  pass  by  the  auriculo-temporal  nerve  to  the  gland. 

Ouataiory  Fibers.  —  According  to  some,  the  chorda  tym- 
pani  really  supplies  the  fibers  to  the  lingual  nerve  that  are  con- 
cerned with  taste. 

It  will  thus  be  seen  that  the  facial  nerve  has  a  great  variety 
of  important  functioiin,  and  that  paralysis  may  be  more  or  less 
serious,  according  to  the  number  of  fibers  involved. 

The  Trigtmimub  TrifMial,  or  Fiflh  Vervt.— This  nerve  has  very 
extensive  functions.  It  is  the  sensory  nerve  of  the  face ;  but, 
as  will  be  seen,  it  is  peculiar,  being  a  combination  of  the  motor 
and  sensory,  or,  in  other  words,  has  paths  for  both  afferent  and 
efferent  impulses.  The  motor  and  less  extensive  division  arises 
from  a  nucleus  in  the  floor  of  the  fourth  ventricle.  I'li"  sen- 
sory, much  the  larger,  seems  to  have  a  very  wide  origin.  The 
nerve-fibers  may  be  traced  from  the  pons  Varolii  through  the 
medulla  oblongata  to  the  lower  boundary  of  the  olivary  body 
and  to  the  posterior  horn  of  the  spinal  cord.  This  origin  sug- 
gests a  resemblance  to  a  spinal  nerve,  the  motor  root  eorre- 
spcading  to  the  anterior,  and  the  sensory  to  a  posterior  root, 
the  more  so  as  there  is  a  large  ganglion  connected  with  the 
sei  fory  part  of  the  nerve  within  the  brain-case. 

Ejf<"nt  Fibers. — 1.  Motor. — ^To  certain  muscles  (1)  of  mas- 
tkisbioit  :«n^poral,  masseter,  pterygoid,  mylohyoid,  and  the 
fi : urior  part  of  the  digastric.  2.  Secretory. — To  the  lachrymal 
fr'Ajid  of  the  ciphthalmic  division  of  this  nerve.  3.  Vaso-motor. 
— Probably  to  Ahe  ocular  vessels,  those  of  the  mucous  mem- 
brane of  the  cheek  and  g^ms,  etc.  4.  Trophic. — From  the  re- 
sults ensuing  on  section  of  this  nerve,  it  has  been  maintained 
that  it  contains  special  trophic  fibera  We  have  discussed  this 
subject  in  an  earlier  chapter. 

Afferent  Fibers.— 1.  Sensory.— To  the  entire  face.  To  par- 
ticularize regions :  1.  The  whole  of  the  skin  of  the  face  and 
that  of  the  anterior  surface  of  the  external  ear.  2.  The  external 
auditory  meatus.  3.  The  mucous  lining  of  the  cheeks,  the  floor 
of  the  mouth,  and  rfhe  anterior  region  of  the  tongue.  4.  The 
teeth  and  periosteum  idf  the  jaws.  6.  The  lining  membrane  of 
the  entire  nasal  cavity.  <6.  The  conjunctiva,  globe  of  the  eye, 
and  orbit.    7.  The  dura  mater  throughout. 

Many  of  these  afl!eient  .flbers.are,  of  course,  intimately  oon- 


i.    Speech  is 

by  the  super- 
i,  from  which 
;he  gland, 
chorda  tym- 

that  are  con- 
great  variety 
)  more  or  less 
d. 

erve  has  very 
he  face;  but, 

of  the  motor 
1  afferent  and 
iivision  arises 
jle.  Tli"  Ben- 
)  origin.    The 

through  the 

olivary  body 
is  origin  sug- 
)i'  root  corre- 
losterior  root, 
cted  with  the 

9B  (1)  of  mas- 
toid, and  the 
bhe  lachrymal 
i.  Vaso-motor. 
mucous  mem- 
From  the  re- 
m  maintained 
discussed  this 

•ace.  To  par- 
the  face  and 
.  The  extermd 
leeks,  the  floor 
ngue.  4.  The 
:  membrane  of 
be  of  the  eye, 

itimately  con- 


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Collection  de 
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Canadian  Instituta  for  Historical  Microreproductions  /  Institut  Canadian  da  microraproductions  historiquas 


i*sfiU-':ji*i'^w^iH<*' 


/ 


THE  GEREBRO-SPINAL  SYSTEM  OF  NERVES. 


681 


cemed  with  reflexes,  as  sneezing,  winking,  etc.    Certain  secre- 
tory acts  are  often  excited  through  this  nerve,  as  lachrymation. 


Tta.  4n.— Limiti  of  eatHMOH  dirtiflmtton  of  MMOfy  dmtw  to  tow,  hMd,  and  neck  (after 
BCdard).  1,  cutaneoaa  dletribotion  of  (^thalmic  divWon  of  fllltii  nerre  >  S,  of  aaperior 
nwKillMrjr  dmiim ;  S,  8,  of  inferior  mudllMT;  4,  of  witeriar  bmodMa  of  oervlcal  nerree ; 
8,  S,  of  poeterior  iMHMlMi  of  oerrioal  aerrea. 


when  the  nasal  mucous  membrane  is  stimulated ;  indeed,  the 
paths  for  afferent  impulses  giving  rise  to  reflexes,  including 
secretion,  are  very  numerous. 

Oustatory  impulses  from  the  anterior  end  and  lateral  edges 
of  the  tongue  are  conveyed  by  the  lingual  (gustatory)  branch 
of  this  nerve.  Many  are  of  opinion,  however,  that  the  fibers 
of  the  chorda  tympani,  which  afterward  leave  the  lingual  to 
imite  with  the  facial  nerve,  alone  convey  such  impressions. 
The  subject  can  not  be  regarded  as  quite  settled.  Tactile  sensi- 
biUity  in  the  tongue  is  very  pronounced,  as  we  have  all  experi- 
enced when  a  tooth,  etc.,  has  for  some  reason  presented  an  un- 
usual surface  quality,  and  beo<Hne  a  source  of  constant  offense 
to  the  tongue. 

The  ganglia  of  the  fifth  nerve,  so  far  as  the  functions  of 
their  cells  are  concerned,  are  enigmatical  at  presmit.  They  are 
doubtless  in  some  sense  trophic  at  least.  With  each  of  these 
are  nerve  connections  (''roots''  of  the  ganglia),  which  seem 
to  contain  different  kinds  of  fibenf.  These  ganglia  are  con- 
nected with  the  main  nerve-centers  by  both  afferent  and  efferent 
nerves,  and  also  witii  the  sympathetic  nerves  themselves.  Some 
regard  the  ganglia  as  the  representatives  of  the  sympathetic 
system  within  the  cranium. 

I.  The  CUiary  {Ophthalmie,  Leniiofdar)  GkmsrZion.— Its  three 
roots  are :  1.  From  the  branch  of  the  third  nerve  to  the  inferior 


wTHIWilliiMilWl,    >- — -< — ■' 


632 


ANIMAL  PHYSIOLOGY. 


oblique  muscle  (motor  root).  2.  From  the  nasal  branch  of  the 
ophthalmic  division  of  the  fifth.  .3.  From  the  carotid  plexus 
of  the  sympathetic.  The  efferent  branches  pass  to  the  iris,  are 
derived  chiefly  from  the  sympathetic,  and  cause  dilatation  of 
the  pupil.    There  are  also  vaso-motor  fibers  to  the  choroid,  iris, 

and  retina.  The  afferent  fibers  are  sen- 
sory, passing  from  the  conjunctiva,  cor- 
nea, etc. 

II.  The  Nasal  or  SpTieno  -  Palaiine 
Oanglion. — The  motor  root  is  derived 
from  the  facial  through  the  great  su- 
perficial petrosal  nerve ;  its  sympathetic 
root  from  the  carotid  plexus.  Both  to- 
gether constitute  the  vidian  nerve.  It 
would  seem  that  afferent  impulses  from 
the  nasal  chambers  pass  through  this 
ganglion.  The  efferent  paths  are :  1. 
Motor  to  the  levator  palati  and  asygos 
uvulfiB.  2.  Vaso-motor,  derived  from  the 
sympathetic.  3.  Secretory  to  the  glands 
of  the  cheek,  etc. 

III.  The  Otic  Cfanglion. — Its  roots 
are:  1.  Motor,  from  the  third  division. 
2.  Sensory,  from  the  inferior  division  of 
the  fifth.  3.  Sympathetic,  from  the 
plexus  around  the  meningeal  artery.  It 
makes  communication  with  the  chorda 
tsrmpani  and  seventh,  and  supplies  the 
parotid  gland  with  some  fine  filaments. 
Motor  fibers  mixed  with  sensory  ones 
pass  to  the  tensor  tympani  and  tensor 
palati. 

IV.  The  SuhnuixiUary  Oanglion. — 
Its  roots  are :  1.  Branches  of  the  chorda 
tympani,  from  which  pass  (a)  secretory 

fibers  to  the  submaxillary  and  sublingual  glands,  (6)  vaso-mo- 
tor (dilator)  fibers  to  the  vessels  of  the  same  glandd.  2.  The 
sympathetic,  derived  from  the  superior  cervical  ganglion,  pass- 
ing to  the  submaxillary  gland.  It  is  also  thought  to  be  the  path 
of  vaso-constrictor  fibers  to  the  gland.  3.  The  sensory,  from 
the  lingual  nerve,  supplying  the  gland  substance,  its  ducts,  etc. 
Pathological. — 1.  The  motor  division  of  the  nerve,  when  the 
medium  of  efferent  impulses,  owing  to  central  disorder,  may 


Fia.  478.  —  Unipolar  cell  from 
Qaawrton  guifrtion  (after 
Schwalbe).  Wv,  If,  nudel 
of  aheath ;  T,  fiber  brandi- 
inK  at  a  node  of  Banvier. 


/ 


THE  CEREBRO-SPINAL  SYSTEM  OF  NERVES. 


633 


'auch  of  the 
otid  plexus 
the  iris,  are 
lilatation  of 
choroid,  iris, 
)ers  are  sen- 
anctiva,  cor- 

no  -  PcikUine 
is  derived 
le  great  su- 
sympathetic 
s.  Both  to- 
n  nerve.  It 
ipulses  from 
ihrough  this 
aths  are :  1. 
i  and  asygos 
ved  from  the 
;o  the  glands 

1. — Its  roots 
ird  division. 
)r  division  of 
0,  from  the 
al  artery.  It 
li  the  chorda 
supplies  the 
lue  filaments, 
sensory  ones 
li  and  tensor 

Ganglion. — 
)f  the  chorda 
(o)  secretory 
,  (6)  vaso-mo- 
mdd.  2.  The 
tnglion,  pass- 
o  be  the  path 
lensory,  from 
its  ducts,  etc. 
ve,  when  the 
isorder,  may 


cause  trismus  (locked-jaw)  from  tonic  tetanic  action  of  the  mus- 
cles of  mastication  supplied  by  this  nerve.  2.  Paralysis  of  the 
same  muscles  may  ensue  from  degeneration  of  the  motor  nuclei 
or  pressure  on  the  nerve  in  its  course.  3.  Neuralgia  of  any  of 
the  sensory  branches  may  occur  from  a  great  variety  of  causes, 
and  often  maps  out  very  exactly  the  course  and  distribution  of 
the  branches  of  the  nerve.  4.  Vaso-motor  disturbances  are  not 
infrequently  associated  with  neuralgia.  Blushing  is  an  evi- 
dence of  the  normal  action  of  the  vaso-motor  fibers  of  the  fifth 
nerve.  5.  A  variety  of  trophic  (metabolic)  disturbances  may 
arise  from  disorder  of  this  nerve,  its  nuclei  of  origin  or  its  gan- 
glia, such  as  grayness  and  loss  of  hair  (imperfect  nutrition), 
eruptions  of  the  skin  along  the  course  of  the  nerves,  etc.  Atro- 
phy of  the  face,  on  one  or  both  sides,  gradual  and  progressive, 
may  occur.  Such  affections,  as  well  as  others,  point  in  the  most 
forcible  manner  to  the  influence  of  the  nervous  system  over  the 
metabolism  of  the  body. 

The  OloMOi^haryiigeal  or  Hinth  Vtnre.— This  nerve,  together 
with  the  vagus  and  spinal  accessory,  constitutes  the  eighth 
pair,  or  rather  trio.  Functionally,  however,  they  are  quite  dis- 
tinct. 

The  glosso-pharyngeal  arises  in  the  floor  of  the  fourth  ven- 
tricle above  the  nucleus  for  the  vagus.  It  is  a  mixed  nerve 
with  efferent  and  afferent  fibers :  1.  llfferent  fibers,  furnishing 
motor  fibers  to  the  middle  constrictor  of  the  pharynx,  stylo- 
pharyngeus,  levator  palati,  and  asygos  uvulae.  2.  Afferent 
fibers,  which  are  the  paths  of  sensory  impulses  from  the  base 
of  the  tongue,  the  soft  palate,  the  tonsils,  the  Eustachian  tube, 
«ympanum,  and  anterior  portion  of  the  epiglottis.  Stimulation 
of  the  regions  just  mentioned  gives  rise  reflexly  to  the  move- 
ments of  swallowing  and  to  reflex  secretion  of  saliva. 

This  nerve  is  also  the  special  nerve  of  taste  to  the  back  of 
the  tongue. 

The  PnevnogMtri^  Vaipii,  or  Tenth  Verve.— Most  of  the  func- 
tions of  this  nerve  have  already  been  considered  in  previous 
chapters. 

In  some  of  the  lower  vertebrates  (sharks)  the  nerve  arises 
by  a  series  of  distinct  roots,  some  of  which  remain  separate 
throughout.  This  fact  explains  its  peculiarities,  anatomical 
and  functional,  in  the  higher  vertebrates.  In  these  there  have 
been  concentration  and  blending,  so  that  what  seems  to  be  one 
nerve  is  really  made  up  of  several  distinct  bundles  of  fibers, 
many  of  which  leave  the  main  trunk  later. 


I  iMWimiiwiM  i*wwf^t»MiiftfiiilMi  I  ■-•  ■ 


(**.'.■-. 


6M 


ANIMAL  PHYSIOLOGY. 


It  may  be  regarded  as  the  most  complicated  nerve-trunk  in 
"the  body,  and  the  distribution  of  its  fibers  is  of  the  most  exten- 
sive character.  Following  our  classification  of  efferent  and 
afferent,  we  recognize : 

1.  Efferent  fibers,  which,  are  motor  to  an  extensive  tract  in 
the  respiratory  and  alimentary  regions. 

Thus  the  constrictors  of  the  pharynx,  certain  muscles  of  the 
palate,  the  oesophagus,  the  stomach,  and  the  intestine,  receive 
an  abundant  supply  from  this  source.  By  the  laryngeal  nerves, 
probably  derived  originally  from  the  spinal  accessory,  the  mus- 
cles of  the  larynx  are  innervated.  The  muscles  of  the  trachea, 
bronchi,  etc.,  are  also  supplied  by  the  pneumogastric.  It  is 
probable  that  vaso-motor  fibers  derived  from  the  sympathetic 
run  in  branches  of  the  vagus.  The  relations  of  this  nerve  to 
the  heart  and  lungs  have  already  been  explained. 

2.  Afferent  Fibers. — It  may  be  said  that  afferent  impulses 
from  all  the  regions  to  which  efferent  fibers  are  supplied  pass 
inward  by  the  vagus.  One  of  the  widest  tracts  in  the  body  for 
afferent  impulses  giving  rise  to  reflexes  is  connected  with  the 
nerve-centers  by  the  branches  of  this  nerve,  as  evidenced  by 
the  many  well-known  phenomena  of  this  character  referable 
to  the  pharynx,  larynx,  lungs,  stomach,  etc.,  as  vomiting,  sneez- 
ing, coughing,  etc.  This  nerve  plays  some  important  part  in 
secretion,  no  doubt,  but  what  that  is  has  not  been  as  yet  well 
established. 

Pathologtcal. — Section  of  both  vagi,  as  might  be  expected, 
leads  to  death,  which  may  take  place  from  a  combination  of 
pathological  changes,  the  factors  in  which  vary  a  good  deal 
with  the  class  of  animals  the  subject  of  experiment.  Thus,  the 
heart  in  some  animals  (dog)  beats  with  great  rapidity  and 
tends  to  exhaust  itself.  In  birds  especially  is  fatty  degenera- 
tion of  heart,  stomach,  intestines,  etc.,  liable  to  follow. 

Paralysis  of  the  muscles  of  the  larsmx  renders  breathing 
laborious.  From  loss  of  sensibility  food  accumulates  in  the 
pharynx  and  finds  its  way  into  the  larynx,  favoring,  if  not 
actually  exciting,  inflammation  of  the  air-passages. 

But  it  is  not  to  be  forgotten  that  upon  the  views' we  advo- 
cate as  to  the  constant  influence  of  the  nervous  system  over 
all  parts  of  the  bodily  metabolism,  it  is  plain  that  after  section 
of  the  trunk  of  a  nerve  with  fibers  of  such  wide  distribution 
and  varied  functions  the  most  profound  changes  in  so-called 
nutriucn  must  be  expected,  as  well  as  the  more  obvious  func- 
tional derangements ;  or,  to  put  it  otherwise,  the  results  that 


THE  CEREBR0-8PINAL  8YSTEM  OP  NERVES. 


686 


erve-trunk  in 

le  most  exten- 

efferent  and 

nsive  tract  in 

Quscles  of  the 
Bstine,  receive 
jrngeal  nerves, 
sory,  the  mus- 
f  the  trachea, 
gastric.  It  is 
>  sympathetic 
this  nerve  to 

irent  impulses 
supplied  pass 
I  the  body  for 
cted  with  the 
evidenced  by 
cter  referable 
miting,  sneez- 
>rtant  part  in 
m  as  yet  well 

i  be  expected, 
>mbination  of 
r  a  good  deal 
at.  Thus,  the 
rapidity  and 
btty  degenera- 
Uow. 

ers  breathing 
ulates  in  the 
iroring,  if  not 

)S. 

lews' we  advo- 
i  system  over 
t  after  section 
e  distribution 
«  in  so-called 
obvious  func- 
e  results  that 


follow  are  in  themselves  evidence  of  the  strongest  kind  for  the 
doctrine  of  a  constant  neuro-metabolic  influence  which  we  ad- 
vocate. It  will  not  be  forgotten  that  the  depressor  nerve,  which 
exerts  reflexly  so  important  an  influence  over  blood-pressure, 
is  itself  derived  from  the  vagus. 

The  Spinal  AooeMory  or  Sltrenth  Htrw.— This  nerve  arises 
from  the  medulla  oblongata  somewhat  far  back,  and  from  the 
spinal  cord  in  the  region  of  the  fifth  to  the  seventh  vertebra. 
Leaving  the  lateral  columns,  its  fibers  run  upward  between  the 
denticulate  ligament  and  the  posterior  roots  of  the  spinal  nerve 
to  enter  the  cranial  cavity,  which  as  they  issue  from  the  cra- 
nium subdivide  into  two  bundles,  one  of  which  unites  with  the 
vagus,  while  the  other  pursues  an  independent  course  to  reach 
the  stemo-mastoid  and  trapezius  muscles,  to  which  they  fur- 
nish the  motor  supply ;  so  that  it  may  be  considered  function- 
ally equivalent  to  the  anterior  root  of  a  spinal  nerve.  The 
portion  joining  the  vagus  seems  to  supply  a  large  part  of  the 
motor  fibers  of  that  nerve. 

Pathological.— Tonic  contraction  of  the  flexors  of  the  head 
causes  wry-neck,  and  when  they  are  paralyzed  the  head  is  drawn 

to  the  sound  side. 

The  EypogloMl  or  Twdfth  Verro.— It  arises  from  the  lowest 
part  of  the  calamus  scriptorius  and  perhaps  from  the  olivary 
body.  The  manner  of  its  emergence  between  the  anterior 
pyramid  and  the  olivary  body,  on  a  line  with  the  anterior  spi- 
nal roots,  suggests  that  it  corresponds  to  the  latter ;  the  more  so 
as  it  is  motor  in  function,  though  also  containing  some  vaso- 
motor fibers,  in  all  probability  destined  for  the  tongue.  Such 
sensory  fibers  as  it  may  contain  are  derived  from  other  sources 
(vagus,  trigeminus).  It  supplies  motor  fibers  to  the  tongue  and 
the  muscles;  attached  to  the  hyoid  bone. 

Pteffcotof/tcoi.— Unilateral  section  of  the  nerve  gives  rise  to 
a  corresponding  lingual  paralysis,  so  that  when  the  tongue 
is  protruded  it  points  to  the  injured  side;  when  being  drawn 
in,  the  reverse.  Speech,  singing,  deglutition,  and  taste  may 
also  be  abnormal,  owing  to  the  subject  being  unable  to  make 
the  usual  co-ordinated  movements  of  the  tongue  essential  for 
these  acts. 


686 


ANIMAL  PHYSIOLOGY. 


Relations  of  the  Cerebro-spinal  and  Sympathetic 

Systems. 

No  division  of  the  nervous  system  has  been  so  unsatisfactory, 
because  so  out  of  relation  with  other  parts,  as  the  sympathetic. 
It  was  also  desirable  to  attempt  to  co-ordinate  the  cerebral  and 
spinal  nerves  in  a  better  fashion ;  and  various  attempts  in  that 
direction  have  been  made.  Very  recently  a  plan,  by  which  the 
whole  of  the  nerves  issuing  from  the  brain  and  cord  may  be 
brought  into  a  unity  of  conception, has  been  proposed;  and, 
though  it  would  be  premature  to  pronounce  definitely  as  yet 
upon  the  scheme,  yet  it  does  seem  to  be  worth  while  to  lay  it 
before  the  student,  as  at  all  events  better  than  the  isolation 
implied  in  the  three  divisions  of  the  nerves  which  has  been 
taught  hitherto. 


Fw.474. 


Flo.  47& 
Fio.  l7S.-aMigUonceU  fn>m  Rsrmpathetle  iiaiiidton  of  f rogr :  gNAtly  tnAgnifled,  and  ihowtiig 

both  •tntlgnt  wid  uoUed  flben  (after  Quain). 
Fio.  474.— Multipolar  miutllmi  oella  from  a^mpathetic  nritem  of  man,  hlghlr  magnlfled  (after 

XaK  Scbultae).   a,  oMl  freed  from  capaule ;  b,  Inokwed  within  a  mioleated  caiMole.   In 

both  the  prooeta  hare  been  broken  away. 

Instead  of  the  classification  of  nerves  into  efferent  and 
afferent,  connected  with  the  anterior  aud  the  posterior  horns 


THE  CEREBRO-SPINAL  SYSTEM  OP  NERVB& 


687 


HPATHETIO 

insatisfactory, 
Q  sympathetic, 
e  cerebral  and 
tempts  in  that 
,  by  which  the 
d  cord  may  be 
)ropo8ed;  and, 
(finitely  as  yet 
while  to  lay  it 
1  the  isolation 
hich  has  been 


lAgnifled,  and  ihowtiig 

liigUjr  magnWed  (after 
nuolcated  caiwule.   In 


l;o  efferent  and 
posterior  horns 


of  the  gray  matter  of  the  spinal  cord,  another  division  has 
been  proposed,  viz.,  a  division  of  nerve-fibers  and  their  centers 
of  origin  in  the  gray  matter  for  the  supply  of  the  internal 
and  the  external  parts  of  the  body — i.  e.,  into  splanchnic  and 
somatic  nerves.  The  centers  of  origin  of  the  splanchnic  nerves 
are  referred  to  groups  of  cells  in  the  gray  matter  of  the  cord 
around  the  central  canal;  while  the  somatic  ner\'es  spring 
from  the  gray  cornua  and  supply  the  integument  and  the 
ordinary  muscles  of  locomotion,  etc.  The  splanchnic  nerves 
supply  certain  muscles  of  respiration  and  deglutition,  derived 
from  the  embryonic  lateral  plates  of  the  mesoblast ;  the  somatic 
nerves,  muscles  formed  from  the  muscle-plates  of  the  same 
region. 

It  is  assumed  that  the  segmentation  of  the  vertebrate  and 
invertebrate  animal  is  related ;  and  that  segmentation  is  pre- 
served in  the  cranial  region  of  the  vertebrate,  as  shown  by  the 
nerves  themselves. 

The  afferent  fibers  of  both  splanchnic  and  somatic  nerves 
pass  into  the  spinal  ganglion,  situated  in  the  nerve-root,  which 
may  be  regarded  as  stationary. 

It  is  different  with  the  anterior  roots.  Some  of  the  fibers 
are  not  connected  with  ganglia  at  all ;  others  with  ganglia  not 
fixed  in  position,  but  occurring  at  variiible  distances  from  the 
central  nervous  system  (these  being  the  so-called  sympathetic 
ganglia) :  thus,  the  anterior  root-fibers  are  divisible  into  two 
groups,  both  of  which  are  efferent,  viz.,  ganglionated  and  non- 
ganglionated.  The  ganglionated  belong  to  the  splanchnic  sys- 
tem, and  have  relatively  small  fibers ;  the  non-ganglionated  in- 
cludes both  somatic  and  splanchnic  nerves,  composing  the 
ordinary  nerve-fibers  of  the  voluntary  striped  muscles  of  respi- 
ration, deglutition,  and  locomotion. 

It  would  appear  that  these  now  isolated  ganglia  have  been 
themselves  derived  from  a  primitive  ganglion  mass  situated  on 
the  spinal  nerves ;  so  that  the  dis+^Jiotion  usually  made  of  gan- 
glionated and  non-ganglionated  rt-f';.  is  not  fundamental. 

A  spinal  nerve  is,  then,  formed  v.f — 1.  A  posterior  root,  the 
ganglion  of  which  is  stationary  in  position,  and  connected  with 
splanchnic  and  somatic  nerves,  both  of  which  are  afferent.  2. 
An  anterior  root,  the  ganglion  of  which  is  vagrant,  and  con- 
nected with  the  efferent  small-fibered  splanchnic  nerves. 

Among  the  lower  vertebrates  both  anterior  and  posterior 
roots  pass  into  the  same  stationary  ganglion.  Such  is  also  the 
case  in  the  first  two  cervical  nerves  of  the  dog» 


688 


ANIMAL  PHTSIOLOOY. 


»y 


Does  the  above-mentioned  plan  of  distribution,  etc.,  hold 
for  the  cranial  nerves  ? 

Leaving  out  the  nerves  of  special  sense  (olfactory,  optic, 
and  auditory),  the  other  cranial  nerves  may  be  thus  divided : 
1.  A  foremost  group  of  nerves,  wholly  efferent  in  man,  viz., 
the  third,  fourth,  motor  division  of  the  fifth,  the  sixth,  and 
seventh.  2.  A  hindmost  group  of  nerves  of  mixed  character, 
viz.,  the  ninth,  tenth,  eleventh,  and  twelfth. 

The  nerves  of  the  first  group,  since  they  have  both  large- 
fibered,  non-ganglionated  motor  nerves,  and  also  small-fibered 
splanchnic  efferent  nerves,  with  vagrant  ganglia  (ganglion 
oculomotorii,  ganglion  geniculatum,  etc.),  resemble  a  spinal 
nerve  in  respect  to  their  anterior  roots.  They  also  resemble 
spinal  nerves  as  to  their  posterior  roots,  for  at  their  exit  from 
the  brain  they  pass  a  ganglion  corresponding  to  the  stationary 
posterior  ganglion  of  the  posterior  root  of  a  spinal  nerve. 
These  being,  however,  neither  in  roots  nor  ganglion  functional, 
are  to  be  regarded  as  the  phylogenetically  (ancestrally)  degen- 
erated remnants  of  what  were  once  functional  ganglia  and 
nerve-fibers ;  in  other  words,  the  afferent  roots  of  these  nerves 
and  their  ganglia  have  degenerated. 

The  hindmost  group  of  cranial  nerves  also  answers  to  the 
spinal  nerves.  They  arise  from  nuclei  of  origin  in  the  medulla 
and  in  the  cervical  region  of  the  spinal  cord,  directly  continu- 
ous with  corresponding  groups  of  nerve-cells  in  other  parts  of 
the  spinal  cord ;  but  in  these  nerves  there  is  a  scattering  of  the 
components  of  the  corresponding  spinal  nerves.  Certain  pecul- 
iarities of  these  cranial  nerves  seem  to  become  clearer  if  it  be 
assumed  that,  in  the  development  of  the  vertebrate,  degenera- 
tion of  some  region  once  functional  has  occurred,  in  conse- 
quence of  which  certain  portions  of  nerves,  etc.,  have  disap- 
peared or  become  functionless. 

It  is  also  to  be  remembered  that  a  double  segmentation 
exists  in  the  body,  viz.,  a  somatic,  represented  by  vertebree  and 
their  related  muscles,  and  a  splanchnic  represented  by  visceral 
and  branchial  clefts,  and  that  these  two  have  not  followed  the 
same  lines  of  development ;  so  that  in  comparing  spinal  nerves 
arranged  in  regard  to  somatic  segments  with  cranial  nerves, 
the  relations  of  the  latter  to  the  somatic  muscles  of  the  head 
miist  be  considered;  in  other  words,  like  must  be  compared 
with  like. 


L- 


THE  VOICE  AND  SPEECH. 


tion,  etc.,  hold 

[factory,  optic, 
thus  divided: 
t  in  man,  viz., 
the  sixth,  and 
Lxed  character, 

ve  both  large- 

0  small-fibered 
glia  (ganglion 
imble  a  spinal 
f  also  resemble 
their  exit  from 
>  the  stationary 
\  spinal  nerve, 
lion  functional, 
astrally)  degen- 
al  ganglia  and 
}f  these  nerves 

answers  to  the 
.  in  the  medulla 
irectly  continu- 

1  other  parts  of 
cattering  of  the 

Certain  pecul- 

clearer  if  it  be 

brate,  degenera- 

irred,  in  conse- 

)tc.,  have  disap- 

le  segmentation 
jy  vertebrae  and 
ated  by  visceral 
lot  followed  the 
ag  spinal  nerves 
cranial  nerves, 
cles  of  the  head 
ist  be  compared 


THE  VOICE  AND  SPEECH. 

It  is  convenient  to  speak  of  the  singing  voice  and  the  speak- 
ing voice,  though  there  is  no  fundamental  difference  in  their 
production. 

Since  musical  tones  can  be  produced  by  instruments  greatly 
resembling  those  of  the  human  voice,  it  becomes  evident  that 
in  explaining  the  human  voice  we  must  take  large  account  of 
the  principles  of  physics. 

It  is  to  be  remembered  that  sound  is  to  us  an  affection  of  the 
nervous  centers  through  the  ear,  as  the  result  of  a§rial  vibra- 
tions. 

We  are  now  to  explain  how  such  vibrations  are  caused  by 
the  vocal  mechanisms  of  animals  and  especially  of  man. 

The  tones  of  a  piano  or  violin  are  demonstrably  due  to  the 
vibrations  of  their  strings ;  of  a  clarionet  to  the  vibration  of  its 
reed.  But,  however  musical  tones  may  be  produced,  we  dis- 
tinguish in  them  differences  in  pitch,  quantity,  and  quality. 

The  pitch  is  dependent  solely  upon  the  number  of  vibrations 
within  a  given  time  as  one  second ;  the  quantity  or  loudness 
upon  the  amplitude  of  the  vibrations,  and  the  quality  upon  the 
form  of  the  vibrations.  The  first  two  scarcely  require  any  fur- 
ther notice ;  but  it  is  rather  important  for  our  purpose  to  under- 
stand clearly  the  nature  of  quality  or  timbre,  which  is  a  more 
complex  matter. 

If  a  note  be  sounded  near  an  open  piano,  it  may  be  observed 
that  not  only  the  string  capable  of  giving  out  the  correspond- 
ing note  passes  into  feeble  vibration,  but  that  several  others 
also  respond.  These  latter  produce  the  over-tones  or  partials 
which  enter  into  notes  and  determine  the  quality  by  which  one 
instrument  or  one  voice  differs  from  another.  In  other  words, 
every  tone  is  in  reality  compound,  being  composed  of  a  funda- 
mental tone  and  overtones.  These  vary  in  number  and  in  rela- 
tive strength  with  each  form  of  instrument  a6d  each  voice ; 
and  it  is  now  customary  to  explain  the  differences  in  quality  of 
voices  solely  in  this  way ;  and  this  is,  no  doubt,  correct  in  the 
main ;  but  when  two  individuals,  using  successively  the  same 
violin,  play  a  scale  nearly  equal  in  loudness  and  as  much  alike 
in  all  respects  as  possible,  are  we  to  explain  our  ability  to  dis- 
criminate when  the  one  or  the  other  may  be  playing  (out  of 
our  sight)  solely  by  the  overtones  ?  To  answer  this  would  lead 
us  into  very  complex  considerations,  and  we  only  raise  the 


(}40 


ANIMAL  PHYSIOLOGY. 


\: 


question  to  keep  the  mind  of  the  stuiient  open  to  new  or  pos- 
sible additional  factors  in  the  explanation. 

What  are  the  mechanisms  by  which  voice  is  produced  in 
man  ?  Observation  proves  that  the  following  are  essential:  1. 
A  certain  amount  of  tension  of  the  vocal  cords  (bands).    2.  A 

certain  degree  of  approximation  of 
their  edges.  3.  An  expiratory  blast 
of  air. 

It  will  be  noted  that  these  are 
all  conditions  favorable  to  the  vi- 
bration of  the  vocal  bands.  The 
greater  the  tension  the  higher  the 
pitch;  and  the  more  occluded  the 
glottic  orifice  the  more  effective 
the  expiratory  blast  of  air. 

The  principle  on  which  the  vo- 
cal bands  act  may  be  illustrated  in 
the  simplest  way  by  a  well-known 
toy,  consisting  of  an  elastic  bag  tied 
upon  a  hollow  stem  of  wood,  across 
which  rubber  bands  are  stretched, 
and  the  vibration  of  which  caused 
by  the  air  within  the  distended 
bag  gives  rise  to  the  note.  The  stu- 
dent who  would  really  understand 
the  mechanism  of  voice-production 
in  man,  should  not  only  acquire  a 
thorough  knowledge  of  the  anato- 
my of  the  larynx,  especially  of  its 
muscles  and  their  individual  ac- 
tion, but  by  means  of  the  laryngo- 
scope become  familiar  with  the  ap- 
pearances of  the  glottis  and  adja- 
cent parts  during  pronation.  The 
latter  is  not  difficult,  and  auto- 
laryngoscopy  or  self-examination 
may  be  made  instructive  beyond  what  can  be  indicated  in  any 
text-book. 

In  order  to  acquire  a  knowledge  of  the  human  larynx,  we 
recommend  the  dissection  of  the  larynx  of  a  pig,  this  being 
more  like  the  organ  of  man  than  is  that  of  the  sheep  or  most 
other  animals.  It  is  especially  important  to  reccgnize  the  na- 
ture, extent,  and  effect  on  the  vocal  bands  of  the  movements  of 


Pie.  475.— LonKttudliial  aaeUoa  of  hu- 
Duui  Uujax  (after  8«ppej).  1,  Ten- 
triole  of  Iwryax ;  S,  mperior  vocal 
oord;  S,  Inferior  vocal  cord;  4,  aryt- 
enoid oartilaga ;  5,  wnUoD  of  aryt- 
enoid muMie ;  6,  A,  inferior  portion 
of  cavity  of  larvnx ;  7,  aaetkm  of 
poaterlor  part  of  cricoid  cartUaje ; 
B,  wctioo  of  witerlor  part  of  aame ; 
0,  superior  border  of  cricoid  car- 
tilage ;  10,  Motion  of  thjrold  car- 
tUaKe;  11,  11,  nperior  portion  of 
cavity  of  larynx ;  U,  18,  arytenoid 
gland;  14,  lA,  epiglotda;  16,  17, 
adipoee  tiame:  18,  aection of  hyoid 
bone;  19, 18, 80,  trachea. 


THE  VOICE  AND  SPEECH. 


641 


to  new  or  pos- 

is  produced  in 
ire  essential:  1. 
i  (bands).  2.  A 
)proximation  of 
jxpiratory  blast 

I  that  these  are 
irable  to  the  vi- 
5al  bands.  The 
1  the  higher  the 
re  occluded  the 
more  effective 
it  of  air. 

>n  which  the  vo- 
be  illustrated  in 
by  a  well-known 
a  elastic  bag  tied 
a  of  wood,  across 
ds  are  stretched, 
of  which  caused 
a  the  distended 
lenote.    Thestu- 
eally  understand 
voice-production 
)t  only  acquire  a 
Ige  of  the  anato- 
,  especially  of  its 
ir  individual  ac- 
8  of  the  laryngo- 
iliar  with  the  ap- 
glottis  and  adja- 
pl^onation.    The 
Bcult,  and   auto- 
self-examination 
J  indicated  in  any 

iiuman  larynx,  we 
a  pig,  this  being 
the  sheep  or  most 
reccgnize  the  na- 
the  movements  of 


no.  m.  ^^-  *"• 

tf&top^aSJneSTo'f  ^riSvlK^^     muMle ;  4.  facet  of  the  artlcuUtlon  of  small 
-  -        -  --  -'"-  -rlcoW  < 


cornu  of  thyroid  cartilage  with  cri 


most  marked  around  a  ver- 


the  arytenoid  cartilages.  These  are 
tical  axis,  giving  rise  to  an  inward 
and  outward  movement  of  rota- 
tion, but  there  are  also  movements 
of  less  extent  in  all  directions.  It 
is  in  fact  through  the  movements 
of  these  cartilages  to  which  the 
vocal  bands  are  attached  posteri- 
orly, that  most  of  the  important 
changes  in  the  tension,  approxi- 
mation, etc.,  of  the  latter  are  pro- 
duced. The  lungs  are  to  be  regarded 
as  the  bellows  furnishing  the  neces- 
sary wind-power  to  set  the  vocal 
bauds  vibrating,  while  the  larynx 
has  respiratory  as  well  as  vocal 
functions,  as  has  been  already 
learned.  Assuming  that  the  stu- 
dent has  a  good  knowledge  of  the 
41 


lC-o^ 


^»^ 


Fio.  478.— Larynx,  Tiewed  from  above, 
o?Sir«aiaiiiiction  (after  Huxley^ 
Th,  ithyroid  cartilage :  Cr,  cricoid 
cartilARe ;  V,  edges  of  vocal  llgar 
mentcibouDdlDg  gloMa;  Ary, a^te- 
noid  cartilages ;  Tfc.^.  tt>y«-«3««: 
nold  mimcfe:  C.a.l.  lateral  crico- 
arytenoid muscle ;  C.a.p,  posterior 
crfco-arytenold  muscle ;  Ar.p,  po( 
terior  arytenoid  muscles. 


poe- 


642 


ANIMAL  PHYSIOLOGY. 


general  anatomy  of 
the  larynx,  we  call 
attention  briefly  to 
the  following : 

Widening  of  the 
glottis  is  effected  by 
the  crico  -  arytenoi- 
JcMS  posticus  pull- 
ing outward  the  pro- 
cessus vocalis  or  at- 
tachment posterior- 
ly of  the  vocal  band, 
and  a  similar  effect 
is  produced  by  the 
■s     arytenoideus   posti- 
S     cus  acting  alone. 

Narrowing  of  the 
sfe«     glottis     is     accom- 
B 11     plished  by  the  crico- 
|«|     arytenoideiks    later- 
iM     alis,  and  the  follow- 
ing    when     acting 
either  singly  (except 
the       arytenoideus 
posticus),  or  in  con- 
ceri;,  as  the  sphinc- 
gSg     ter   of  the  larynx, 
||L  viz.,  the  thyro-aryt- 
«5||  enoidem     extemus, 
||l  thyro  •  arytenoideus 
'  -'  irUemv^,  thyro-ary- 
epiglotticus,    aryte- 
noideus posticus. 
Tension  of  the  vo- 
^e$  col  bands  is  brought 
al-S  about  by  the  sphinc- 
^  ^  ter  group,  and  espe- 
cially by  the  exter- 
nal and  internal  thy- 
_  ro  -  arytenoid  mus- 
f^  cles. 
^|g^       Htrre     Supplj.— 
a   as  The  superior  laryn- 


mVHapilHCM 


THE  VOICE  AND  SPEECH. 


643 


al  anatomy  of 
irynx,  we  call 
bion  briefly  to 
>llowing : 
^idening  of  the 
is  eflfected  by 
yrico  -  arytenoi- 
posticu3  pull- 
utward  the  pro- 
s  vocalis  or  at- 
nent  posterior- 
the  vocal  band, 
a  similar  effect 
•oduced  by  the 
inoideus   posti- 
icting  alone. 
harrowing  of  the 
is     is     accom- 
led  by  the  crico- 
enoideus    later- 
and  the  follow- 
when     acting 
er  singly  (except 
aryteiioideus 
iicus),  or  in  con- 
;,  as  the  sphinc- 
of  the  larynx, 
,  the  thyro-aryt- 
ideus     extemus, 
ro  •  arytenoideus 
imua,  thyro-ary- 
glotticua,     aryte- 
deus  posticus. 
Tension  of  the  vo- 
bands  is  brought 
mt.by  thesphinc- 
group,  and  espe- 
lly  by  the  exter- 
and  internal  thy- 
•  arytenoid  mus- 

3. 

Htnre     Supply.— 

e  superior  laryn- 


geal contains  the  motor  fibers  for  the  crico-thyroid  (possibly 
also  the  arytenoideus  posticus)  and  also  supplies  the  mucous 
membrane.  The  inferior  laryngeal  supplies  all  the  other  mus- 
cles. While  both  of  these  nerves  are  derived  from  the  vagus, 
their  fibers  really  belong  to  the  spinal  accessory.  It  is  worthy 
of  note  that  the  entire  group  of  muscles  making  up  the  sphinc- 
ter of  the  larynx  is  contracted  when  the  inferior  laryngeal  is 
stimulated. 

Above  the  true  vocal  bands  lie  the  so-called  false  vocal 
bands  (cords)  which  take  no  essential  part  in  voice-production. 
Between  these  two  pairs  of  bands  are  the  ventricles  of  Morgagni, 
which,  as  well  as  the  adjacent  parts,  secrete  mucus  and  allow 
of  the  movements  of  both  sets  of  bands  and  in  so  far  only  as- 
sist in  phonation. 

What  is  tho  nature  of  the  nervous  connections  by  which 
the  muscular  movements  necessary  for  voice-production  is  ac- 
complished. They  are  certainly  more  complex  in  nature,  at 
least  in  all  their  highest  manifestations,  than  might  at  first 
appear. 

Volition  is  unquestionably  the  starting-point,  but  the  result 
is  modified  by  a  great  variety  of  afferent  impulses,  including 
those  from  the  larynx  and  'supra-laryngeal  cavities,  the  thorax, 
lungs,  even  the  ear,  and  possibly  the  eye.  Muscular  co-ordina- 
tions of  the  most  delicate  kind  must  be  effected,  seeing  the  fine 
shades  in  pitch  and  quality  which  a  first-rate  singer  can  pro- 
duce. 

To  watch,  with  the  laryngoscope,  these  changes  in  the  vocal 
bands  alone,  gives  one  an  idea  of  the  complexity  and  perfection 
of  such  adjustments  which  no  verbal  description  can  convey. 
It  is  impossible  for  a  deaf  man,  or  one  defective  in  sensibility 
in  the  regions  concerned  in  phonation,  to  produce  good  musical 
tones.  No  doubt  one  bom  blind,  and  without  those  stored 
experiences  derived  from  countless  pictures,  can  but  very  im- 
perfectly make  adaptations  in  singing  dependent  on  such  ex- 
perience ;  and  one  has  only .  to  hear  deaf-mutes,  who  have 
learned  to  speak  from  imitation  of  the  speech-movements  of 
normal  persons,  to  become  convinced  of  how  important  a  part 
the  ear  plays  in  vocalization.  The  efforts  of  such  persons  near- 
ly always  seem  to  be  out  of  harmony  with  the  surroundings. 

There  are  many  subjects  connected  with  the  production  of 
the  singing-voice  especially  which  have  been  matters  of  ani- 
matied  controversy,  chiefly  because  investigators  have  restricted 
their  observations  to  on  unduly  limited  range  of  facts. 


644 


ANIMAL  PHYSIOLOOT. 


The  whole  of  the  supra-laryngeal  cavities,  the  trachea  and 
bronchial  tubes,  may  be  regarded  as  resonant;e-chambers,  the 
former  of  which  are  of  the  most  importance,  so  far  as  the 
quality  of  the  voice  is  concerned.  There  seems  to  be  little 
doubt  that  they  have  much  to  do  with  determining  the  differ- 
ences by  which  one  individual's  voice  at  the  same  pitch  differs 
from  another ;  nor  is  the  view  that  they  may  have  a  slight  in- 
fluence on  the  pitch  of  the  voice,  or  even  its  intensity,  to  be 
ignored. 

The  epiglottis,  in  so  far  as  it  has  any  effect,  in  all  probability 
modifies  the  voice  in  the  direction  of  quality. 

The  range  of  any  one  voice  in  pitch  is,  of  course,  much  less 
than  what  may  be  termed  the  human  vocal  limit — i.  e.,  the 
range  of  the  deepest,  the  intermediate,  and  the  highest  voices 
combined. 

The  following  graphic  representation  will  serve  a  good  pur- 
pose. It  will  be  observed  that  the  extreme  limits  are  tones  of 
about  eighty  and  one  thousand  vibrations  per  second,  respect- 
ively. 

I Soprano. 1024 


m 


CkmtraTto. 


684 


I 


EFOAS       cdefgab      cK  d' e' r  g' a' b' 


^ 


^ 


rr 


o"  d"  e"  I"  g"  a"  b"  o'" 


80 


BaaB. 


842 


VSd 


tenog. 


51S 


Fla.  4S.— Thlg  flgure  lUuatimtea  Um  range  of  the  different  kinds  of  voices,  and  the  number  of 
▼ibrationa  aaswwinK  to  the  oompaas  of  each.  llieUiiiitahereUMUoatedare.otoouiae.iiot 
absolute. 


TIm  Begiittn  and  fhe  lUwtto-YoiM.— Among  points  most  dis- 
puted even  yet  are  the  registers  and  the  falsetto-voice.  The 
subject  of  registers  turns  upon  the  answer  to  the  question. 
What  is  the  natural  method  of  producing  tones  ?  All  admit 
that  they  may  be  sung  with  different  vocal  mechanisms,  so  to 
speak — i.  e..  that  different  persons,  as  a  matter  of  fact,  do  not 
co-ordinate  the  various  parts  of  the  larynx  in  quite  the  same 
way.  In  attempting  to  settle  a  question  of  this  character  a 
good  deal  of  difference  in  individuality  must  be  allowed  for ; 
and,  given  equally  effective  results,  viewed  artistically,  that 


THE  VOICE  AND  SPEECH. 


645 


le  trachea  and 
•chambers,  the 
so  far  as  the 
as  to  be  little 
ing  the  diflfer- 
le  pitch  differs 
ve  a  slight  in- 
tttensity,  to  be 

all  probability 

arse,  much  less 

limit — i.  e.,  the 

highest  voices 

rve  a  good  pur- 
its  are  tones  of 
second,  respect- 


ao. 


1024 


684 


n 


"  e"  £"  g"  a"  b"  c" 


loM,  and  the  number  of 
oMed  M«,  of  coime,  not 


points  most  dis- 
etto-voice.  The 
bo  the  question, 
les  ?  All  admit 
jchanisms,  so  to 
•  of  fact,  do  not 
I  qxiite  the  same 
this  character  a 
;  be  allowed  for ; 
artistically,  that 


may  be  considered  as  the  natural  method  of  singing  a  certain 
range  of  notes  which  leads  to  the  least  expenditure  of  energy ; 
and  certain  rules  may  be  laid  down  for  the  average  man,  with, 
however,  a  good  deal  of  latitude  for  special  cases,  as  we  have 
said.    But  certainly  any  method  that  disorders  the  larynx  or 


mTuif^  of  f e^  ditting  production  of  head-tonem  aa  seen  V  tbe  author, 

the  general  health  can  not  be  correct.  Hence  clinical  and 
pathological  observations  become  of  great  importance.  One 
of  the  commonest  faults  consists  in  persons,  whose  laryngeal 
mechanism  does  not  permit  of  the  necessary  changes  within 
the  power  of  those  specially  endowed,  using  a  method  of  voice- 
production  for  higher  tones,  which  is  really,  in  their  case  at 
least,  adapted  only  to  lower  ones,  hence  straining,  congestions, 
fatigue,  catarrh,  and  a  host  of  attendant  evils. 

It  does  not  come  within  our  province  to  treat  of  the  artistic 
side  of  the  question ;  but  we  may  point  out  that  nearly  all  the 
compositions  of  the  greatest  masters  of  music  are  written  with- 
in a  comparatively  small  range  of  notes ;  and  when  it  is  remem- 
bered that  these  are  such  as  are  most  heard  in  the  intercourse 
of  daily  life  by  the  speaking-voice,  or  at  least  do  not  depart 
widely  from  them,  we  may  understand  how  it  is  that  such 
music  has  ever  stirred,  and  does  still  appeal  to,  the  heart  (and 
ear)  of  man  so  generally,  alike  in  the  cultivated  and  unculti- 
vated. . 

Attempts  have  been  made  to  explain  the  falsetto-votce  by 
the  action  of  the  vocal  bands  alone ;  but  any  one  who  will  com- 
pare his  sensations,  his  consciousness  of  altered  muscular  ar- 
rangement, and  consequent  changed  relative  position  of  parts 
in  the  supra-laryngeal  cavities,  even  without  the  use  of  a 
laryngoscope  at  all,  can  not  fail  to  perceive  that  the  vocal 


646 


ANIMAL  PHYSIOLOGY. 


I 


bands  are  not  alone  to  be  taken  into  account.    But  there  can 
be  no  question  of  a  very  great  difference  in  the  behavior  of  the 


Fio.484. 


Flo.  485. 


Flo  «4.-LaiTniH)«»plc  view  of  the  Riotti*  durlnflr  emtorion^  hlfdh-pitcbpd  note*  (I«  Bon). 
1 T  bwe  S  touKue ;  8, 4.  eplglotlfi :  N  8,  ph«ryiut ;  7,  arytenoid  car«U««» ;  8,  opening 

cun^wm^rtili«e ;  1«,  "uperior  vooiU  cordu;  18,  inferior  tociU  corda (tenda). 
Fio.  4n!-OtotS^irSMn  Cj  lMyngo«»pe  during  production  of  cheat-Toloe  (after  MMidl  and 
Gratmer). 

vocal  bands  in  the  production  of  the  falsetto  as  compared  with 
the  chest  voice. 

As  has  been  suggested,  in  the  higher  tones  of  the  falsetto, 
the  vocal  bands  are  shortened  and  come  together  posteriorly,  at 
all  events ;  and  this  may  be  produced  largely  by  the  action  of  the 
thyro-arytenoideus  intemus,  and  possibly  several  other  mus- 
cles. There  is  little  doubt  that  the  whole  breadth  of  the  bands 
does  not  share  in  the  vibrations.  In  many  of  its  features,  the 
high  falsetto  of  the  male  voice  is  allied  in  production  to  the 
head- voice  of  females,  in  which  only  the  central  parts  of  the 
bands  seem,  in  the  highest  notes,  to  be  involved. 

In  nearly  all  previous  considerations  of  this  topic,  it  seems 
to  us  that  insufficient  attention  has  been  paid  to  the  method  of 
applying  the  blast  of  air  by  the  lungs.  The  great  importance 
of  this  in  playing  wind-instruments  is  practically  recognized, 
yet  in  our  own  wind-instrument,  the  most  perfect  of  all,  it  has 
received  too  little  practical,  and  still  less  theoretical,  attention. 

FttiholiogiflaL— The  results  of  the  paralysis  of  the  several 
muscles  of  the  larynx,  of  the  soft  palate,  etc.,  throw  a  certain 
amount  of  light  upon  this  subject;  it  is  not  to  be  forgotten, 
however,  that  in  this  instance,  as  in  others,  the  usual  (normal) 
mechanism  may  be  obscured  through  adaptations  by  unusual 
methods,  so  that  the  best  is  made  of  a  bad  case : 

1.  When  the  widening  of  the  glottis  can  not  take  place,  and 
the  glottic  opening  assumes  the  cadaveric  position,  owing  to  pa- 
ralysis of  the  crico-arytenoidei  postici,  there  may  be  dyspnoea. 
8.  Paralysis  of  the  arytenoideiM  iransversua,  in  consequence  of 


THB  VOICB  AND  SPEECH. 


647 


But  there  can 
ahavior  of  the 


.48S. 

ttohrdnotMdieBoii). 

«rtiU«w ;  8,  opening 

tage  of  Santorinl ;  11, 

d«<bMKU). 

rotoe  (after  Kuul  and 


compared  with 

of  the  falsetto, 
•  posteriorly,  at 
he  action  of  the 
ral  other  mus- 
th  of  the  bands 
xs  features,  the 
oduction  to  the 
al  parts  of  the 

topic,  it  seems 
the  method  of 
eat  importance 
Uy  recognized, 
;t  of  all,  it  has 
ical,  attention, 
of  the  several 
irow  a  certain 
)  be  forgotten, 
usual  (normal) 
>n8  by  unusual 

bake  place,  and 
n,  owing  to  pa- 
iy  be  dyspnoea, 
consequence  of 


which  the  glottic  opening  can  not  be  sufficiently  narrowed, 
allows  of  undue  escape  of  air,  and  gives  rise  to  feebleness  and 
harshness  of  the  voice.  3.  There  may  be  almost  complete  loss 
of  voice  from  paralysis  of  both  thyro-arytenoid  muscles.  4. 
When  the  crico-thyroid  muscles  are  paralyzed,  owing  to  im- 
perfect tension  of  the  vocal  bands,  the  voice  may  become  lower 
pitched  and  harsh.  Any  form  of  paralysis  of  the  vocal  bands 
should  arrest  attention  and  lead  to  a  careful  examination  of  the 
chest  for  aneurism,  etc.,  and  to  general  inqn  iry,  for  even  the 
brain  may  be  involved. 

The  importance  of  the  muscles,  by  which  the  larynx  is  raised 
and  steadied,  must  not  be  overlooked.  In  professional  singers 
from  constant  practice  they  often  become  greatly  enlarged. 
We  may  here  remark  upon  the  value  of  singing  when  not 
pushed  to  the  verge  of  fatigue,  when  free  from  straining,  and 
in  a  pure  atmosphere,  as  a  healthful  exercise,  the  whole  of 
'^hich  does  not  consist  in  the  good  arising  from  the  use  of  the 
chest,  larynx,  etc.,  or  the  additional  amount  of  oxygen  respired, 
but  fJso  from  complicated  and  ill-understood  nervous  effects. 

At  puberty,  in  both  sexes,  the  larynx  shares  in  those  changes 
of  relative  and  absolute  size  which  the  body  then  experiences 
so  generally.  The  thickening  from  excess  of  blood  and  nerv- 
ous energy  produces,  especially  in  youths,  a  harsh  voice,  which 
is,  in  this  instance,  as  in  all  others,  an  indication  of  the  need 
of  rest  of  the  parts.  To  sing  under  such  circumstances  is,  of 
course,  liable  to  induce  permanent  injury  in  the  form  of  weak- 
ness or  harshness  of  voice ;  but  once  this  period  is  passed,  regu- 
lar vocal  gymnastics  may  be  of  great  service  in  perfecting  an 
organ  unrivaled  as  a  musical  instrument,  and  by  means  of 
which  man  is  raised  through  the  endowment  of  speech  vastly 
above  all  other  animals. 

The  subject  of  voice  production  and  voice  preservation  is 
one  of  the  utmost  importance  in  education,  though  it  receives 
comparatively  little  attention.  The  public  taste  for  high- 
pitched  vocalization  does  unquestionably  tend  to  ruin  voices, 
and  is  alike  opposed  to  artistic  and  physiological  principles. 
While  a  few  may  reach  the  prescribed  standard  of  the  public 
taste,  the  many  fail  in  the  attempt. 

OompantiTe. — Much  more  is  ^own  of  the  sounds  emanating 
from  the  lower  animals  than  of  the  mechanisms  by  which  they 
are  produced.  This  applies,  of  course,  especially  to  such  sounds 
as  are  not  produced  by  external  parts  of  the  body,  it  being 
very  difficult  to  investigate  these  experimentally  or  to  observe 


648 


ANIMAL  PHYSIOLOGY. 


the  animal  closely  enough  when  producing  the  various  vocal 
effects  naturally. 

All  of  our  domestic  mammals  have  vocal  bands  and  a  larynx, 
not  as  widely  different  from  that  of  man  as  might  be  supposed 
from  the  feeble  range  of  their  vocal  powers. 

The  actual  behavior  of  the  vocal  bands  has  been  studied 
experimentally  in  the  dog  when  growling,  barking,  etc.  And, 
so  far  as  it  goes,  this  mechanism  of  voice  production  is  not 
essentially  different  from  that  of  man.  Growling  is  the  result 
of  the  functional  activity  of  the  vocal  mechanism,  not  unlike 
that  of  man  when  singing  a  bass  note ;  barking,  of  that  analo- 
gous to  coughing  or  laughing,  when  the  vocal  bands  are  rapidly 
approximated  and  separated. 

The  grunting  of  hogs  and  the  lowing  and  bawling  of  horned 
cattle  is  probably  very  similar  in  production,  so  far  as  the 
larynx  is  concerned,  to  the  above.  The  cat  has  plainly  very 
great  command  over  the  larynx,  and  can  produce  a  wide  range 
of  tones. 

The  quality  of  the  voice  of  most  animals  appears  harsh  to 
our  ears,  owing  probably  to  a  great  preponderance  of  over-tones, 
in  consequence  of  an  imperfect  and  unequal  tension  of  the  vocal 

bands ;  but  the  influence  of  the  su- 
pra-laryngeal  cavities,  often  very 
large,  must  also  be  taken  into  ac- 
count. ' 

In  certain  of  the  primates,  and 
especially  in  the  howling  monkeys, 
large  cheek-pouches  can  be  inflated 
with  air  from  the  larynx,  and  so  add 
to  the  intensity  of  the  note  produced 
by  the  vocal  bands  that  their  voice 
may  be  heard  for  miles.  Song-birds 
Fio.  488.-Lower  tarynx  (Syrinx)  of  produce  their  notes,  as  may  be  seen, 
S?m^dde'fT°Sfltm*1S  by  external  movements  low  down  at 
£r^yeUu"rtU?*SS?Sr!  the  bifurcation  of  the  trachea  (sy- 
K^SiuT?!^^"  mSS;  rinx).  The  notes  are  owing  to  the 
SSSrSdJ  fSSS^JSTh  ?^  vibration  of  two  folds  of  the  mucous 
^eteatBie angle  of  biturcalion  membrane,  which  project  into  each 

bronchus,  and  are  regulated  in  their 
movements  by  muscles,  the  bronchial  rings  in  this  region  being 
correspondingly  modified. 

A  large  number  of  species  of  fishes  produce  sounds  and  in 
a  variety  of  ways,  in  which  the  air-bladder,  stomach,  intestines. 


THE  VOICE  AND  SPEECH. 


649 


various  vocal 

9  and  a  larynx, 
it  be  supposed 

I  been  studied 
ng,  etc.  And, 
luction  is  not 
g  is  the  result 
}m,not  unlike 
of  that  analo- 
ids  are  rapidly 

ling  of  horned 
so  far  as  the 
s  plainly  very 
9  a  wide  range 

)ears  harsh  to 
)  of  over-tones, 
on  of  the  vocal 
Qce  of  the  su- 
i,  often  very 
laken  into  ac- 

priraates,  and 
ling  monkeys, 
an  be  inflated 
nx,  and  so  add 
note  produced 
lat  their  voice 
8.  Song-birds 
s  may  be  seen, 
« low  down  at 
e  trachea  (sy- 
owing  to  the 
of  the  mucous 
ject  into  each 
ilated  in  their 
B  region  being 

sounds  and  in 
aoh,  intestines. 


etc.,  take  part.  Most  reptUes  are  voiceless,  in  the  proper  sense, 
though  there  are  few  that  can  not  produce  a  sort  of  hissing 
sound,  caused  by  the  forcible  emission  of  air  through  the  upper 
respiratory  passages. 

Frogs,  as  is  well  known,  produce  sounds  of  great  variety  in 
pitch,  quality,  and  intensity,  some  species  croaking  so  as  to  be 
heard  at  the  distance  of  at  least  a 
mile.  It  is  a  matter  of  easy  ob- 
servation that  when  frogs  croak 
the  capacity  of  the  mouth  cavity 
is  greatly  increased,  owing  to  dis- 
tention of  resonating  sacs  situated 
at  each  angle  of  the  jaws.  When 
tree-frogs  croak,  their  throats  are 
greatly  distended,  apparently  in 
successive  waves.  But  it  is  among 
insects  that  the  greatest  variety 
of  methods  of  producing  sounds  is 
found. 

In  bees  and  flies  sounds  are 
caused  by  the  vibration  of  mus- 
cular reeds  placed  in  the  stigmata 
or  openings  of  their  tracheal  tubes, 
also  by  the  extremely  rapid  vibra- 
tion of  their  wings.  The  death- 
head  moth  is  said  to  force  air  from 
its  sucking  stomach,  and  thus  give 
rise  to  a  sound  in  the  same  way 
as  certain  fishes. 

In  the  grasshopper  a  noise  is 
produced  by  rubbing  its  rough 
legs  against  the  wing-cases,  and  in  allied  forms  (locusts)  by 
moving  the  wing-cases  against  one  another ;  and  in  other  groups 
different  parts  of  the  body  are  brought  into  mutual  contact  or 
rubbed  or  struck  against  foreign  bodies. 

Speech. 

It  may  be  noticed  that  the  differences  of  voices,  by  which 
we  are  enabled  to  discriminate  between  individuals,  are  much 
more  marked  during  speaking  than  singing.  This  is  owing  to 
greater  prominence  of  over-tones  in  the  speaking  voice,  as  may 
be  readUy  shown. 


Fia.  48T.— Portton  of  trachea  or  air-tube 
of  a  caterpillar  (after  Oesenbaur), 
a.  epitlieUal-llke  cellular  layer;  6, 
nuclei.  The  air-tubes  in  insects  are 
kept  up  by  colled  chitinous  tubes, 
as  seen  above ;  ard,  like  the  blood- 
vessels of  mammals,  penetrate  every 
part  of  the  body. 


■:J-- 


650 


ANIMAL  PHYSIOLOGY. 


If  a  series  of  tuning-forks  be  held  before  the  open  moiiih, 
it  will  be  found  that  but  one  position  of  the  buccal  cavity  and 
its  contents  answers  to  a  certain  note,  but  that  when  this  is 
assumed  it  acts  as  a  resonance-chamber;  thus,  for  a  tuning- 
fork  sounding  A,  when  the  cavity  takes  the  shape  necessary 
to  sound  (speak)  that  note,  the  tone  produced  by  the  fork  is 
greatly  augmented  when  the  latter  is  held  before  the  mouth. 
It  has  thus  been  estimated  that  the  fundamental  tones  of  the 
vowel  cavity  are  these :  U  =  b,  O  =  b',  A  =  b'",  I  =  b"".  If  the 
vowels  of  this  series  be  whispered,  their  pitch  rises.  Whisper- 
ing may  be  termed  speech  without  voice — L  e.,  the  vocal  bands 
do  not  vibrate,  but  the  total  effect  is  produced  by  the  blast  (rf 
air  acting  through  the  supra-laryngeal  parts  as  a  resonance 
cavity. 

Now,  if  it  be  true  that  there  is  but  one  position  of  the  supra- 
laryngeal  cavities  that  will  give  a  pure  vowel-sound,  and  this 
sound  corresponds  in  pitch  to  a  certain  note  of  the  scale,  it 
seems  to  us  that  the  conclusion  that  the  pitch  of  the  voice,  as 
well  as  its  quality,  is  dependent  to  some  extent  upon  these  parts 
as  well  as  the  vocal  bands.  Such  a  view  is,  however,  not  that 
generally  taught.  Every  singer  knows  that  it  is  impossible  to 
produce  certain  vowel-sounds  pure  with  notes  of  a  certain  pitch. 
Usually,  when  the  nasal  cavity  is  shut  off  posteriorly  by  the 
soft  palate,  or  stopped  anteriorly  by  closing  the  nostrils,  a 
change  in  quality  of  the  vowel-sounds,  characterized  as  nasal, 
is  produced ;  but,  as  illustrating  well  that  the  organism  has 
more  ways  than  one  of  accomplishing  the  larger  part  if  not  all 
its  ends,  by  effort,  and  especially  by  practice,  the  vowels  may 
be  sounded  nearly  as  well  as  usual  under  these  unfavorable 
conditions. 

Con«nuuit& — The  sounds  produced  by  the  vocal  bands  may 
be  modified  by  interruption  in  their  formation  or  otherwise, 
though  it  is  plain,  from  what  has  been  said,  that  the  form  of 
tha  mouth,  etc.,  can  not  be  ignored  in  any  form  of  vocalization. 

According  to  the  parts  of  the  supra-laryngeal  cavities  con- 
cerned in  the  modification  referred  to,  may  we  have  the  basis 
of  a  physiological  classification  of  the  consonants,  though  it  is 
obvious  that  they  may  be  dealt  with  on  wholly  different  prin- 
ciples. By  the  first  method,  which  alone  chiefly  concerns  us, 
we  have  a  division  into  lahitda,  denUUa,  and  guUtinUs,  according 
as  the  lips,  teeth,  or  soft  palate  and  pharynx  are  chiefly  con- 
cerned. Of  course,  several  parts  are  involved  in  all  sound-pro- 
duction, and  we  recommend  the  student  to  resort  to  the  forma- 


THE  VOICE  AXD  SPEECH. 


601 


e  openmoaih, 
;cal  cavity  and 
t  when  this  is 

for  a  ttming- 
lape  necessary 
by  the  fork  is 
>re  the  mouth. 
b1  tones  of  the 

=  b"".  If  the 
ses.  Whisper- 
le  vocal  bands 
by  the  blast  ot 
as  a  resonance 

n  of  the  snpra- 
ound,  and  this 
3f  the  scale,  it 
>f  the  voice,  as 
pon  these  parte 
^ever,  not  that 
s  impossible  to 
a  certain  pitch, 
iteriorly  by  the 
the  nostrils,  a 
irized  as  nasal, 
>  organism  has 
■  part  if  not  all 
he  vowels  may 
se  unfavorable 

>cal  bands  may 
1  or  otherwise, 
at  the  form  of 
of  vocalization, 
al  cavities  con- 
have  the  basis 
its,  though  it  is 
different  prin- 
ly  concerns  us, 
inds,  according 
are  chiefly  con- 
i  all  sound-pro- 
rt  to  the  forma- 


tion of  the  vowels  and  consonants  before  a  mirror,  in  order  to 
acquire  a  practical  knowledge  of  the  relative  share  taken  by 
the  different  parts  of  the  supra-laryngeal  vocal  organs.  Ordi- 
narily the  tongue  does,  of  course,  function  as  the  most  impor- 
tant organ  of  speech ;  but  the  extent  to  which  this  organ,  the 
front  teeth,  the  lips,  etc.,  can  by  practice  be  dispensed  with  is 
surprising  in  the  extreme.  Persons  with  more  than  half  of  the 
tongue  removed  manage  to  speak  quite  intelligibly. 

Consonants  may  be  further  classified- according  to  the  nature 
of  the  movements  associated  with  their  formation :  thus,  they 
may  be  either  contimurus  or  explosive,  the  meaning  of  which 
will  be  clear  from  the  classification  given  below,  and  the  basis 
of  the  latter  from  an  inspection  of  the  parts  by  a  mirror  dur- 
ing their  formation,  supplemented  by  consultation  of  our  sen- 
sations at  the  time. 

The  following  tabulation  may  be  of  service,  as  representing 
at  least  certain  aspects  of  the  subject : 
Explosives :  Labials,  P,  B. 
Denials,  T,  D. 
OvMurals,  K,  G. 
Aspirates:     Labials,F,Y. 

Dentals,  L,  S,  Sh,  Th,  Z. 
Qutturdls,  Ch  (as  in  loch),  Gh  (as  in  laugh). 
Besonants:    Lai)ials,M.. 
.  Dentals,  TS. 
OvUurals,  N,  G. 
Vibratory:   Labial. 

Dental,  B  (common). 
Chittural,  B  (guttural). 
It  is  remarkable  that  certain  consonantal  (and  vowel)  sounds 
are  wholly  absent  from  some  languages.  All  are  familiar  with 
the  difficulty  Europeans  find  in  sounding  the  English  th,  as  in 
thin.  Their  vocal  organs  fail  to  make  the  necessary  co-ordina- 
tions, these  not  having  been  practised  in  youth. 

PathologiMa.— Paralysis  of  the  soft  palate,  giving  rise  to  a 
nasal  quality  of  voice,  illustrates  the  importance  of  this  little 
muscular  curtain. 

Stammering  is  believed  to  be  caused  by  long-continued 
spasm  of  the  diaphragm— ^iu  other  words,  upon  tonic  contrac- 
tion of  this  muscle  in  the  inspiratory  position,  usually  depend- 
ent on  some  form  of  psychic  excitement.  Stuttering,  on  the 
other  hand,  is  temporary  inability  to  form  the  sounds  desired ; 
lack  of  co-ordination  of  parts  principally.    The  various  paraly- 


....„j-,- 


652 


ANIMAL  PHYSIOLOGY. 


sea  of  the  vocal  bands  affect  speech  as  well  as  voice,  though 
to  a  less  extent ;  and  whispering  is,  of  course,  always  possible. 

Special  Considerations  and  Summary. 

Evolntion. — The  very  lowest  forms,  and  in  fact  most  inverte- 
brate groups,  seem  to  be  voiceless.  Darwin  has  shown  that 
voice  is,  in  a  large  number  of  groups,  confined  either  entirely 
to  the  male,  or  that  it  is  so  much  more  developed  in  him  as  to 
become  what  he  terms  a  "  sexual  character."  There  is  abundant 
evidence  that  males  are  chosen  as  mates  by  the  females,  among 
birds  especially,  not  alone  for  superiority  in  beauty  of  plumage, 
but  also  for  their  song.  Thus,  by  a  process  of  natural  selection 
(sexual  selection),  the  voice  would  tend  to  improve  with  the 
lapse  of  time,  if  we  admit  heredity,  which  is  an  undeniable  fact, 
even  among  men — whole  families  for  generations,  as  the  Bachs, 
having  been  musicians. 

One  can  also  understand  why  on  these  principles  voice 
should  be  especially  developed  in  certain  groups  (birds),  while 
among  others  (mammals)  form  and  strength  should  determine 
sexual  selection,  the  strongest  winning  in  the  contests  for  the 
possession  of  the  females,  and  so  propagating  their  species  under 
the  more  favorable  circumstances  of  chance  of  the  most  desira- 
ble females. 

Pathology  teaches  that,  when  certain  parts  of  the  brain 
(speech-centers)  of  man  are  injured  by  accident  or  disease,  the 
power  of  speech  may  be  lost.  From  this  it  is  evident  that  the 
vocal  apparatus  may  be  perfect  and  yet  there  be  no  speech ;  so 
that  it  becomes  comprehensible  that  the  vocal  powers  of,  e.  g., 
a  dog,  are  so  limited,  notwithstanding  his  comparatively  highly 
developed  larynx.  He  lacks  the  energizing  and  directive  ma- 
chinery situated  in  the  brain. 

Some  believe  that  there  was  a  period  when  man  did  not  pos- 
sess the  power  of  speech  at  all ;  and  many  are  convinced  that 
the  human  race  has  undergone  a  gradual  development  in  this 
as  in  other  respects.  Certain  it  is  that  races  differ  still  very 
widely  in  capacity  to  express  ideas  by  spoken  words. 

We  may  regard  the  development  of  a  race  of  speaking  ani- 
mals as  dependent  upon  a  corresponding  advance  in  brain- 
structure,  whether  that  was  acquired  by  a  sudden  and  pro- 
nounced variation,  or  by  gradual  additions  of  increase  in  cer- 
tain regions  of  the  brain,  or  whether  to  the  first  there  was  then 
added  the  second. 


THE  VOICE  AND  SPEECH. 


66$ 


as  voice,  though 
always  possible. 

UMARY. 

Fact  most  inverte- 
has  shown  that 
id  either  entirely 
oped  in  him  as  to 
'here  is  abundant 
e  females,  among 
auty  of  plumage, 
natural  selection 
nprove  with  the 
I  undeniable  fact, 
>ns,  as  the  Bachs, 

principles  voice 
ps  (birds),  while 
hould  determine 
contests  for  the 
eir  species  under 
the  most  desira- 

•ts  of  the  brain 
t  or  disease,  the 
evident  that  the 
)e  no  speech ;  so 
powers  of,  e.  g., 
iratively  highly 
id  directive  ma- 

lan  did  not  pos- 
convinced  that 
lopment  in  this 
differ  still  very 
ords. 

>f  speaking  ani- 
'ance  in  braiii- 
idden  and  pro- 
ncrease  in  cer- 
there  was  then 


It  is  not  unlikely  that,  whether  sexual  selection  has  played 
any  considerable  part,  natural  selection  at  all  events  has  had 
not  a  little  to  do  with  the  preservation  of  those  individuals 
and  races  that  soonest  and  most  fully  developed  the  speech-cen- 
ters ;  for  it  is  to  be  remembered  that  the  principle  of  correlated 
growth  must  be  taken  into  account.  In  nature  generally,  as  in 
social  life,  success  very  frequently  leads  to  success.  As  man's 
superiority  over  the  highest  of  the  mammals  below  him  is 
largely  due  to  his  possession  of  a  speaking  (and  writing)  faculty, 
so  must  we  concede  that  racial  superiority  is  in  part  traceable 
to  the  same  cause.  It  is  well  known  that  the  leaders  among 
savage  tribes  are  frequently  eflEective  in  speech  as  well  as  strong 
of  heart  and  arm. 

This  subject  is  a  very  large,  suggestive,  and  complex  one, 
and  is  worthy  of  some  thought. 

Apart  from  speech  proper,  there  is  a  language  of  the  face 
and  body  generally,  in  which  there  is  much  that  we  share  with 
lower  forms,  especially  lower  mammals.  Darwin,  noticing  this 
resemblance,  regarded  it  as  evidence  strengthening  the  belief 
that  man  is  derived  from  lower  forms.  Why  should  the  forms 
of  facial  expression  associated  with  certain  emotions  so  widely 
among  different  races  of  Inen  be  so  similar  to  each  other  and 
to  those  which  the  lower  animals  employ,  if  there  is  not  some 
community  of  origin  ?  This  is  Darwin's  query,  and  he  con- 
sidered, as  has  been  stated,  that  the  answer  to  be  given  was  in 
harmony  with  his  views  of  man's  origin,  as  based  on  an  alto- 
gether different  sort  of  testimony. 

The  high  functional  development  of  the  hand  and  arm  in 
man,  and  the  ase  of  these  parts  in  writing,  are  suggestive. 

Bnminaiy. — The  musical  tones  of  the  voice  are  caused  by  the 
vibrations  of  the  vocal  bands,  owing  to  the  action  on  them  of 
an  expiratory  blast  of  air  from  the  lungs.  In  order  that  the 
bands  may  act  effectively,  they  must  be  rendered  tense  and  ap- 
proximated, which  is  accomplished  by  the  action  of  the  laryn- 
geal muscles,  especially  those  attached  to  the  arytenoid  car- 
tilages. We  may  speak  of  the  respiratoiy  glottis  and  the 
vocalizing  glottis,  according  as  we  consider  the  position  and 
movements  of  the  vocal  bands  in  respiration  or  in  phonation. 

The  pitch  of  the  voice  is  determined  by  the  length  and  the 
tension  of  the  vocal  bands,  and  frequently  both  shortening  and 
increased  tension  are  combined  ;  perhaps  we  may  say  that  al- 
tered (not  necessarily  increased)  tension  and  length  are  always 
combined. 


fM 


ANIMAL  PHirSIOIiOOY. 


. 


The  quality  of  the  voice  depends  chiefly  upon  the  supra- 
laryngeal  cavities. 

The  vocal  bands  of  the  child  and  of  woman,  being  both 
shorter  and  lighter,  account  largely  for  the  differences  in  pitch, 
quality,  and  loudness  of  their  voices  as  compared  with  that  of 
man.  Success  in  vocalization  is  dependent,  not  only  on  a  suit- 
able laryngeal  and  other  mechanism,  but  upon  the  rapidity  and 
completeness  with  which  a  large  number  of  muscular  and  nerv- 
ous co-ordinations  can  be  made.  Speech  may  be  either  reflex 
or  voluntary,  but  for  high-class  results  many  afferent  impulses 
uiust  determine  or  modify  the  nature  of  the  efferent  impulses. 

There  is  no  essential  difference  in  the  mechanism  of  the 
speaking  and  singing  voice ;  in  the  latter,  however,  the  vocal 
bands  take  a  relatively  greater  share  than  in  the  former,  in 
which  the  supra-laryngeal  parts  are  more  concerned.  This 
applies  especially  to  the  utterance  of  consonants,  which  may 
be  classified  according  to  the  part  of  the  above-mentioned  ap- 
paratus that  is  more  especially  employed. 

It  is  important  to  remember  that  in  all  phonation,  in  the 
case  of  man  at  least,  many  parts  combine  to  produce  the  result ; 
so  that  voice-production  is  complex  and  variable  in  mechan- 
ism, beyond  what  would  be  inferred  from  the  apparent  sim- 
plicity of  the  mechanism  involved ;  while  the  central  nervous 
processes  are,  when  comparison  is  made  with  phonation  in 
lower  animals,  seen  to  be  the  most  involved  and  important  of 
the  whole— a  fact  which  the  results  of  disease  of  the  brain  are 
well  calculated  to  impress,  inasmuch  as  interruptions  anywhere 
among  a  class  of  cerebral  connections,  now  known  to  be  very  ex- 
tensive, suffice  to  abolish  voice,  and  especially  speech-production. 

It  is  of  great  practical  moment  for  each  individual  to  recog- 
nize both  the  limit  of  his  natural  powers,  especially  of  his 
range  in  singing,  and  at  the  same  time  to  appreciate  the  large 
margin  there  is  for  improvement,  more  particularly  when  cul- 
tivation of  the  voice  is  commenced  in  childhood,  and  resumed 
soon  after  the  age  of  puberty  is  attained. 

Among  mammals  below  man  the  vocal  bands  and  lar]mgeal 
and  thoracic  mechanism  are  very  similar,  but  less  perfectly 
and  complexly  co-ordinated ;  so  that  their  vocalization  is  more 
limited  in  range,  and  their  tones  characterized  by  a  quality 
which  to  the  human  ear  is  less  agreeable.  Man's  superiority 
as  a  speaking  animal  is  to  be  traced  chiefly  to  the  special  de- 
velopment of  his  cerebrum,  both  generally  and  in  certain 
definite  regions. 


LOCOMOTION'. 


655 


on  the  supra- 

n,  being  both 
Bnces  in  pitch, 
d  with  that  of 
3nly  on  a  suit- 
6  rapidity  and 
alar  and  nerv- 
•e  either  reflex 
)rent  impulses 
ent  impulses, 
lanism  of  the 
ver,  the  vocal 
he  former,  in 
cerned.  This 
)s,  which  may 
nentioned  ap- 

nation,  in  the 
ice  the  result ; 
le  in  mechan- 
ipparent  sim- 
)ntral  nervous 
phonation  in 
important  of 
the  brain  are 
ions  anywhere 
to  be  very  ex- 
sh-production. 
dual  to  recog- 
Bcially  of  his 
late  the  large 
rly  when  cul- 
,  and  resumed 

»nd  lar]mgeal 
less  perfectly 
sation  is  more 
by  a  quality 
's  superiority 
tie  special  de- 
id  in  certain 


B 


1 


LOCOMOTION. 

The  entire  locomotor  system  of  tissues  is  derived  from  the 
embryonic  mew)bla8t.  These  include  the  muscles,  bones,  carti- 
lage, and  ;  onnective  ttiid  fibrous  tissues;  and  the  tissues  that 
make  up  the  vascular  system  or  the  motor  apparatus  for  the 
circula  f  i  on  of  the  blood.  Locomotion  in  the  mammal  is  effected 
by  the  movement  of  certain  bony  levers,  while  the  equilibrium 
of  the  body  is  maintained.  The  whole  series  of  levers  is  bound 
together  by  muscles,  tendons,  ligaments,  etc.,  and  play  over 
one  another  at  certain  points  where  they  are  invested  with  car- 
tilage, and  kept  moist  by  a  se- 
cretion from  the  cells  covering  ^^^a^^^^i^m 
the  synovial    membranes   that        I  A 

form  the  inner  linings  of  joints. 
Cartilage,  a  very  low  form 
of  tissue  destitute  of  blood-ves-  ,1^  ^g^ 

sels,  and  hence  badly  repaired 
when  lost  by  injury  or  disease, 
forms  a  series  of  smooth  sur- 
faces admirably  adapted  for 
joints,  and  especially  fitted  to 
act  as  a  series  of  elastic  buffers, 
and  thus  prevent  shocks.  Bone, 
though  brittle  in  the  dried  state, 
possesses,  when  alive,  a  favora- 
ble degree  of  elasticity,  while 
sufficiently  rigid.  Provision  is 
made  by  its  vascular  periosteum 
and  central  marrow  (in  the  case 
of  the  long  bones),  as  well  as  by 
the  blood-supply  derived  from  no.  490. 

the  nutrient  artery  and  its  rami-  , 

fications  throughout  the  osseous  tissue,  for  abundant  nourish- 
ment, growth,  and  repair  after  injury. 

We  find  in  the  body  of  mammals,  including  man,  examples 
of  all  three  kinds  of  levers.  It  sometimes  happens  that  there 
is  an  apparent  sacrifice  of  energy,  the  best  leverage  not  being 
exemplified ;  but  on  closer  examination  it  will  be  seen  that  the 
weight  must  either  be  moved  with  nice  precision  or  through 
large  distances,  and  these  objects  can  not  be  accomplished  al- 
ways by  the  arrangements  that  would  simply  furnish  the  most 


Fio.  4Mk 


B 


-9 


dsd 


ANIMAL  PHYSIOLOGY. 


powerful  lever.    This  is  illustrated  by  the  action  of  the  biceps 
on  l^ie  forearm. 

It  "s  to  be  remembered  that,  while  the  flexors  and  extensors 
of  a  limb  act  in  a  certain  degree  the  opposite  of  one  another. 


Fia.  4S1.— Skeleton  of  deer.  The  bones  in  the  extremities  of  th's  the  fle«(«wt  of  quadrupeds 
•re  inclined  very  obliquely  toward  each  other  and  toward  the  scapular  and  fliac  boges. 
This  arrangement  increafies  the  leverage  of  the  muscular  system  and  confers  great 
rapidity  on  the  moving  parts.  It  augments  elasticity,  diminishes  shock,  and  indiractly, 
begets  continuity  of  movement,  a,  angle  formed  by  femur  with  ilium ;  6,  angle  fonaed 
by  tibia  and  flbula  with  ttomur ;  c,  single  formed  by  phalanges  with  cannon-bone ;  «.  an^ 
formed  by  humerus  with  scapula ;  7,  ai  "  * 
(Pettigrew). 


angle  farmed  by  radius  and  ulna  with  hmuMus 


there  is  also,  in  all  cases  perhaps,  a  united  action;  the  one 
set,  however,  preponderating  over  the  other,  and  usually  sev- 
eral muscles,  whether  of  the  same  or  different  classes,  act 
together. 

Standing  itself  requires  the  exercise  of  a  large  number  of 
similar  and  antagonistic  muscles  so  coordinated  that  the  line 
of  gravity  falls  within  the  area  of  the  feet.  An  unconscious 
person  falls,  which  is  itself  an  evidence  of  the  truth  of  the 
above  remarks. 

The  following  statements  in  regard  to  the  direction  of  the 
line  of  gravity  may  prove  useful :  1.  That  for  the  head  falls  in 
front  of  the  occipital  articulation,  as  exemplified  by  the  nod- 
ding of  the  head  in  a  drowsy  person  occupying  the  sitting  atti- 
tude. 2.  That  for  the  head  and  trunk  together  passes  behind  a 
line  joining  the  centers  of  the  two  hip-joints,  hence  the  uncor- 
rected tendency  of  the  erect  body  of  man  is  to  fall  backward. 
3.  That  for  i]\e  head,  trunk,  and  thighs  falls  behind  the  knee> 


:(^«^l«!®ffiaffla8^E?; 


LOCOMOTION. 


657 


.  of  the  biceps 

and  extensors 
f  one  another. 


IP-"^ 


e«t<wt  of  quadrupeds 
ulsr  and  fliac  bobea. 
n  and  confen  great 
ihock,  and  Indlractly 
um ;  0,  angle  f  onaea 
annon-bone;  «.  an^ 
I  ulna  with  huniMvs 


;tion;  the  one 
d  usually  sev- 
nt  classes,  act 

rge  number  of 
id  that  the  line 
.n  unconscious 
9  truth  of  the 

irection  of  the 
te  head  falls  in 
d  by  the  nod- 
he  sitting  atti- 
>asses  behind  a 
ace  the  uncor- 
fall  backward, 
lind  the  knee- 


joints  somewhat,  which  would  also  favor  falling  backward 
(bending  of  the  knees).  4.  The  line  of  gravity  of  the  whole 
body  passes  in  front  pf  a  line  joining  the  two  ankle-joints,  so 
that  the  body  would  tend,  but  for  the  contraction  of  the  mus- 
cles of  the  calves  of  the  legs,  to  fall  forward. 

Taking  these  different  facts  into  consideration  explains  the 
various  directions  in  which  an  individual,  when  erect,  may  fall 
according  as  one  or  the  other  line  (center)  of  gravity  is  dis- 
placed for  a  long  enough  time. 

Walking  (man)  implies  the  alternate  movement  of  each  leg 
forward,  pendulxuu-like,  so  that  for  a  moment  the  entire  body 


4«<T 


8*1011 


It  IS  14 


Fio.  493.— Showa  the  sUnultaaeoua  portions  of  both  lega  during  •  step,  divided  Into  tour 
groupa  (after  Weber).  Firat  group  (A),  4  to  7,  givea  the  different  podtiona  which  the  lega 
■fanultaneoualy  aaram»  while  botn  are  on  the  ground ;  leoond  group  (B).  8  to  11,  ahowa 
the  varioua  poaitiona  of  both  lega  at  tho  time  when  the  poaterior  leg  la  elevated  from  the 
ground,  but  behind  the  supported  one ;  third  group  (C),  IS  to  14,  shows  the  positions 
which  the  lega  asauine  when  the  awloging  leg  overtakea  the  standing  one ;  and  the  fourth 
group  (m,  1  to  a.  the  poaittons  during  the  time  when  the  swinging  leg  Is  propelled  in 
advance  of  the  resting  one.  The  letters  a,  6,  and  «  Indioate  the  aoglsa  fonned  I7  the 
bonea  of  the  right  leg  when  engaged  in  making  a  step :  tiie  letteis  m,  •»,  and  o,  the  poai- 
tiona assumed  bytherlght  foot  when  the  trunk  is  rolliiig  over  It:  0,  shows  the  rotating 
forward  of  the  trunk  upon  the  lett  foot  (/)  aa  an  axlB  ;*,  diowa  the  rotating  forwards 
the  left  leg  and  foot  npon  the  tnrok  (a)  aa  an  uds. 


Ite.  401— Overhand  swlminlng  (FetUgrew). 

must  be  supported  on  one  foot.    When  the  right  foot  is  lifted 
or  swimg  forward,  the  left  must  support  the  weight  of  the 

43 


mstmtvmatmifmt 


658 


ANIMAL  PHYSIOLOGY. 


FM.  4M.— BmuMrprairiiMwIth 


to  ntMarhIa  dtfleniit  pMM  (Iburcr). 


body.    It  becomes  oblique,  the  heel  being  raised,  the  toe  still 
resting  on  the  ground;  and  it  is  upon  this  as  a  fulcrum  that 


Flo.  «^^■-In■tn^^^— t  *"  w>c«^«r  Twrtkiri  rwwtloiM  durlBK  rwekm  paw  (Itowy). 


LOCOMOTION. 


659 


temApnemOUnj)- 

ad,  the  toe  still 
%  fulcrum  that 


^ 


■  IMOMdUMr). 


the  body-weight  is  moved  forward,  when  a  similar  action  is 
taken  up  by  the  opposite  leg. 

It  follows  that  to  prevent  a  fall  there  must  be  a  leaning  of 
the  body  to  one  side,  so  that  the  line  of  gravity  may  pass 
through  each  stationary  foot.  It  follows  that  a  walking  person 
describes  a  series  of  vertical  curves  with  the  head,  and  of  hori- 
zontal ones  with  the  body,  the  resulting  total  being  complex. 

The  peculiarities  of  the  gait  of  different  persons  are  natu- 
rally determined  by  their  height,  length  of  leg,  and  a  variety 
of  other  factors,  which  are  often  inherited  with  great  exactness. 
We  instinctively  adopt  that  gait  which  economizes  energy, 
both  physical  and  mental. 

Running  differs  from  walking,  in  that  both  feet  are  for  a 
period  of  the  cycle  off  the  ground  at  the  same  time,  owing  to 
a  very  energetic  action  of  the  foot  acting  as  a  fulcrum. 

Jumping  implies  the  propulsion  of  the  body  by  the  impulse 
given  by  both  feet  at  the  same  moment. 

Hopping  is  the  same  act  accomplished  by  the  use  of  one 
leg. 

Oonpurativ*. — ^The  movements  of  quadrupeds  are  naturally 
very  complicated,  but  have  now  been  well  worked  out  by 


.-^y 


Vloa.  488  mM  «>7.-«liowliw  the  more  OT  leM  perpenmoular  diraetiaii  of  ttte  itroke  of  the  wi^ 
in  the  fflcht  of  the  Mmngull}:  bow  the  wing  u  Kradually  extended  aa  it  la  devated  (e,f,g)i 
how  it  deaoenda  aa  •  long  terer  untit  it-  aanunea  the  poaition  indicated  by  h ;  how  it  is 
flemd  toward  dw  tennination  of  tbedown-«trok«,a8aaowDath,i,i,  to  convert  it  into  a 
abort  leTer  (a,  b)  and  nrepare  it  for  m^dng  the  up-atroke.  Tbe  dUTerenoe  in  the  length  of 
the  wtec  durtaig  Hexlon  and  eztenaion  ia  indicated  hy  Ute  iihort  and  long  leTera  a,  b  and 
e,  <t.  The  auddm  oonvMriimi  of  the  wing  from  a  hmg  into  a  abort  torer  at  the  end  of  the 
down-atroke  ia  of  great  importance,  aa  It  roba  the  wing  of  tta  momwitnm  and  preparea  it 
for  reveraing  ita  moremenla  (INsttigrew). 

the  use  of  instantaneous  photography.  Even  the  bird's  flight 
is  no  longer  a  wholly  unsolved  problem,  but  is  fairly  well 
understood.  The  movements  of  centipeds  and  other  many- 
legged  invertebrates  are  highly  complicated,  while  their  rapid 


■nvrxxstOMMNIQI 


f^ 


660 


ANIMAL  PHYSIOLOGY. 


Fioa.  «8»nd«9«lKW  that  when  the  wtogii  are  elevaUrf(«V.  9).  the  body  fWtoW;  md  that 
whS  Oe  wiun  an  dep««K>d  <*,  O.  the  body  to  elevated  (r).  ?1«.  488  ihowa  that  the 
wtaun  ara  eleratod  aa  ihort  leven  (e)  uutU  toward  the  termination  of  the  upstroke,  when 
thCT  are  giwhially  expwided  (/. «)  to  nrepare  them  f or  m^iM  U»e  dowiwit«*e.  ^ 
i^ws  thtt  theirinn  dMoend  u  bmtc  leven  (ft)  unUl  toward  the  termlnatton  of  the  down- 
atroke,  when  they  are  Kradually  folded  or  flexed  (i,  J)  to  rob  them  of  thirir  momratam  and 
prepare  them  for  makSng  the  up-ataroke.  .OcnnjMUPe  with  Mga.  4Q6and  4W ..  ^S«»  "««*• 
&e  lUr  beneath  the  winga  is  Tigoroualy  aeiied  during  the  down-^ke,  while  th«t  aboye  it 
h  avoided  dnrinc  the  upstroke.  The  ooncavo-oonvex  form  of  uie  wings  Mid  the  forward 
travel  of  tlie  body  contributea  to  this  result  The  wings,  it  will  be  obsenred,  act  as  a  para- 
diute  both  during  the  up  and  down  strokea.  Fig.  «W  shows  also  the  compound  rotation 
of  the  whig,  howlt  rotates  upon  a,  as  a  center,  with  a  radius  at,  b,  n,  and  upon  a,  e,  b  aa 
a  center,  witb  a  radhis  fc,  i  (mtigrew). 

movements  are  to  be  accounted  for  by  the  multiplicity  of  their 
levers  rather  than  the  rapidity  with  which  they  are  moved. 


FM.  BOft-ChUHngham  buU  (Bos  Sootteas). .  Shows  powwfut  heavy  body,  ud  the  smaU 
eztreiStlMadapted  for  land  tranrit  Also  the  flgure-of-8  movenynta  made  by  the  feet 
and  Unba  in  waU^  and  running.  u,t,ourveamadebyrMit«iid  MtMrtolcreztoemi- 
ttas- r  roureaHuBe  by  rii^rtMd  ikt  posterior  ez^^  The  right  fore  md^Uw 
Mt  ^d%^mo^tMitiSer&^tk>rm  the  waved  Uiie(t,  tt) :  the  left  tore  and  the  rts^t  Und 
toM  move  together  wlorm  the  waved  line  (r.t).  TheourveB(oraudbytheaiileite(t,w) 
and  paalMJcir(r,  s)  eztramitieB  form  eUlpacs  (PsttlgMw). 


LOCOMOTION. 


661 


The  length  and  flexibility  of  their  bodies  must  also  be  taken 
into  account,  rendering  many  legs  necessary  for  support.    We 


/ 


7  fkllii  («) ;  and  that 
;.4Wdiowatiiatthe 
the  upstroke,  when 
nm-Dtvoke.  Fia.tfB 
tnation  of  the  down- 
heir  momentum  and 
407.  By  this  means 
,  while  Oiat  aboye  it 
Dgs  and  the  forward 
ervadi  act  as  a  para- 
)Oompound  rotation 
,  and  upon  a,  c,  b  as 


>licity  of  their 
>y  are  moved. 


I 


iMdy,  and  the  small 
Bts  made  hj  the  feet 
Mt  anterior  eztraml- 
«  rlc^  fore  and  Uw 
we  and  the  riidit  hind 
ibytbeanMrtorlt,*) 


Fra.  801.— Bepnaentatlon  of  bone  at  walking  paoedfafsgr). 

can  only  briefly  refer  to  the  method  of  locomotion  well  exem- 
plified by  our  domestic  quadrupeds.  However,  the  whole  sub- 
ject will  become  plainer  after  a  careful  study  of  the  cuts  intro- 
duced in  this  chapter. 


FW.  am-Horselnaotor  trattfav.  Inttila,aa  toaU  the.otlisrpaws.thebodyof.aiahorse> 
levered  forward  by  a  diagonal  twistina  of  trunk  and  extremities,  the  extremities  describ- 
ing a  flgure-of -8  traekUmrt).  The  llgun-ef -8  is  produced  by  the  attentate  plaar  of  Uie 
^remffies  and  feet,  two  of  which  are  always  on  the  ground  (a,  b).  llius  the  right  fore- 
foot describee  the  eurre  maiiLsd  (.the  left  hind-foot  that  marked  r,  left  for»«Mt  that 
marked  «,  and  riiriit  hind-foot,*.  Tha  (set  on  ground  in  the  present  Instance  are  left  f era 
aad  ria^thiad  (Kttigrew). 


ir 


662 


ANIMAL  PHYSIOLOGY. 


In  walking,  quadrupeds  like  the  horse  use  the  limbs  alter- 
nately, and  in  a  diagonal  sequence,  so  that  the  right  fore-leg 


Fio  508.— Red-throated  dragon  (Draco  kcematopootm.  Gray),  shows  •  Iwfte  inembranoaa 
eSSin^(M)^i»irtSrbeJi^im  anterior  (d,Wiu>A  poSwIof  extremlttM,  Md  ™pp«Mted 
to^  ribs.   The  dnunn  by  thto  •rrancement  cu  take  ext^rive  hsm  with  fierfect  safety. 

Fw.'*M^?lylng  tem^nS&ttlec^ 


^^^^^^^  §»),ttkmwtQimrerytUi^tim5re»M(awarfmBg.  Thewnfaceerooaedhy  the 
Satexoeefi  £at  dlsplued  by  muqrinsecta  and  birds.  Tto  winn  of  ^  bat  aro  deei^ 
S5m»»SiSd»«SelQethew£Siofhe^  The 

bo^ot  the  arm  (r).  forearm  {S^and^hw?  (». ». »)  »'  «»  V^.5S*??**™^^2'»kI 
Sick  margtai  and  the  rzttemttr  of  the  wing,  and  may  not  inaptly  be  compared  to  the 
nemires  In  correapondlng  positions  in  wing  (n  beetle  (Fetngrew). 

and  the  left  hind-leg  are  associated.    Trotting  corresponds  to 
running  in  man,  and  there  is  the  same  diagonal  action.    There 


Fio.  805.-The  bat  (Phtfiwrkina  graeUi;  Peters).  Here  the  t«»'«Unf  ••^•«*  ,<»"*«  J^*^,?) 
areenormouBly  Inweaaed  as  compared  with  that  of  Uw  land  and  water  antmala  generally 
(Pettlgrew),    r,  arm ;  d,  forearm ;  e/, »  n  n,  hand  of  bat. 

is  also  a  gait  natural  to  some  horses,  some  dogs,  the  camel,  etc., 
termed  ambling,  or  pacing,  characterized  by  both  legs  on  the 
same  side  working  simultaneously  and  alike.  This  is  perhaps 
comparable  to  human  walking.  In  galloping,  all  four  feet  are 
ofiE  the  ground  together  for  a  portion  of  the  cycle,  though  they 
do  not  strike  the  ground  again  at  the  same  moment. 

Evolution.— It  is  noteworthy  that  with  almost  all  quadrupeds 
the  gallop  is  the  natural  method  for  rapid  propulsion.    In  all 


MAN  CONSIDERED  PHTSIOLOOICALLT. 


668 


limbs  alter- 
ight  fore-leg 


large  membranooa 
tttea,  and  supported 
with  perfect  lafety. 
ir  tiie  membnuioiis 
ported  by  the  neck, 
flying  lemur  takes 
he  bifi,  I^v^ofl^i^*!* 
Face  ezpoaed  by  the 
:  the  batare deeply 
-winged  birds.  toB 
orttne  antorior  or 
le  compMed  to  the 


orresponds  to 
ction.    There 


animals,  either  bred  by  man  to  attain  great  speed,  as  the  race- 
horse and  greyhound,  or  those  that  have  become  so  by  the  pro- 
cess of  natural  selection,  the  entire  conformation  of  the  body 
has  been  modified  in  harmony  with  the  changes  that  have  taken 
place  in  the  legs  and  feet.  This  is  seen  in  the  greyhound  among 
domestic  animals,  and  in  the  wild  deer  of  the  plain  and  forest. 
Such  instances  illustrate  not  only  the  principle  of  natural  se- 
lection as  a  whole,  but  the  subordinate  one  of  correlated 
growth. 

Any  one  observing  the  modes  of  locomotion  of  quadrupeds, 
especially  horses  and  dogs,  will  perceive  the  advantages  of  the 
four-legged  arrangement.  Not  only  is  there  a  variety  of  modes 
of  progression,  as  walking,  trotting,  galloping,  cantering,  the 
alternations  of  which  permit  of  rest  to  certain  groups  of  mus- 
cles, with  their  corresponding  nervous  connections,  etc.,  but  on 
occasion  some  of  these  animals  can  progress  fairly  well  with 
three  legs.  Sometimes  it  may  also  be  noticed  that  a  horse  that 
prefers  one  gait,  as  pacing,  for  his  easy,  slow  movements,  will 
break  into  a  trot  when  pushed  to  a  higher  rate  of  speed. 

Trotting  can  not  be  considered  the  natural  gait  for  high 
speed  in  the  horse,  yet,  by  a  process  of  "artificial  selection" 
(by  man)  from  horses  that  have  shown  capacity  for  great  speed 
by  this  mode  of  progression,  strains  of  racers  have  been  bred, 
showing  that  even  an  acquired  mode  of  locomotion  may  be 
hereditary ;  while  that  galloping  is  the  more  natural  mode  of 
locomotion  of  the  horse  is  evident,  among  other  things,  by  the 
tendency  of  even  the  best  trotting  racers  to  break  into  a  gallop 
when  unduly  pushed — an  instance  also  of  an  hereditary  tend- 
ency of  more  ancient  origin  prevailing  over  one  more  recent. 

The  bipedal  modes  of  progression  of  birds  are  naturally 
very  like  those  of  man.  « 


(rdef,annn) 

»r  animals  generally 


he  camel,  etc., 
h  legs  on  the 
[lis  is  perhaps 
1  four  feet  are 
),  though  they 
int. 

,11  quadrupeds 
alsion.    In  aU 


MAN  0ONSIDEBE3)  PHTSIOLOOICALLT  AT  THB  DIFFEBENT 
PERIODS  OF  HIS  EXISTENCE. 

Growfh. — As  a  result  of  the  intra-uterine  development  of 
two  cells,  neither  of  which  is  visible  by  the  naked  eye,  the 
human  being  reaches  about  one  third  of  its  total  length  and 
one  twentieth  of  its  maximum  weight.  In  the  infant  the  rela- 
tively larger  size  of  the  head  and  face  is  obvious,  while  among 
internal  organs  the  liver  is  especially  large.  The  child's  future 
inci«ase  in  weight  is  chiefly  from  growth  of  muscles.    Increase 


.™--:i>->i-^^V™K35SW*a 


664 


ANIMAL  PHTSIOLOOT. 


s 


in  stature  continues  up  to  about  the  twenty-fifth  year,  though 
the  increase  is  most  rapid  during  infancy  and  puberty,  when, 
in  fact,  the  weight  is  also  greatly  augmented. 

IHgMtiT*  lyitem.— While  it  is  now  established  that  all  of  the 
digestive  secreting  mechanisms  are  active  at  or  shortly  after 
birth,  it  must  be  borne  in  mind  that  these,  like  the  other  organs, 
adapt  gradually  to  the  new  conditions.  This  is  a  matter  of 
practical  importance  in  infant  feeding.  Thus,  while  it  is  true 
that  the  young  infant's  saliva  will  act  on  starch,  it  is  not  to  be 
supposed  that  its  amylolytic  powers  are  equal  to  those  of  the 
adult. 

CHreiiktory  aad  Saspinitary  tyiUaM.— The  babe's  heart  is 
larger  than  that  of  the  adult  relatively  to  its  body-weight,  and 
its  action  more  rapid ;  hence  the  circulation  is  accomplished  in 
a  8hort«r  space  of  time,  an  advantage  when  it  is  considered  that 
the  need  for  oxygen  and  tissue-food  in  the  young  organism  is 
so  great. 

The  respirations  are  correspondingly  rapid,  and  the  actual 
amount  of  the  respiratory  interchanges  is  greater  than  in  adult 
life.  There  appears,  however,  to  be  a  storing  up  of  oxygen — 
i.  e.,  all  of  the  oxygen  used  up  does  not  shortly  appear  again  as 
carbonic  anhydride. 

The  metabolism  of  the  infant  is  very  active,  and  is  spent 
largely  in  construction ;  growth  is  in  excess  of  waste ;  indeed, 
this  feature  is  characteristic  of  the  metabolism  of  all  young 
animals.  There  is,  in  consequence  of  the  excessive  loss  of  heat, 
from  a  relatively  larger  surface  than  in  the  adult,  the  need  for 
a  more  active  metabolism ;  the  young  animal  must  eat  more, 
to  meet  this  waste.  It  is,  moreover,  in  consequence  of  this  fact 
that  infants,  when  not  protected  better  than  adults,  perish  from 
a  fall  in  the  temperature,  which  their  sensitive  organizations 
can  not  endure. 

Immediately  after  birth  the  adaptation  to  the  new  environ- 
ment is  less  perfect  than  at  a  later  period ;  respiration  is  feeble ; 
the  blood  is  imperfectly  aSrated ;  the  temperature  is  lower ;  the 
entire  metabolism  goes  on  but  feebly :  hence  it  is  that  newly 
bom  kittens,  puppies,  etc.,  can  be  immersed  in  water  for  a  con- 
siderable period  (twenty  to  thirty  minutes)  without  drowning. 
The  tissues  do  not  demand  much  oxygen ;  they  live  on  what 
they  already  have  stored  up,  after  that  in  the  blood  is  ex- 
hausted— in  a  word,  they  behave  much  as  they  did  during  intra- 
uterine life.  The  excretions,  as  would  be  supposed  from  the 
rapid  metabolism,  are  more  abundant  than  in  the  adult.    There 


^?  V 


MAN  CONSIDERED  PHTSIOLOOICALLT. 


666 


year,  though 
uberty,  when, 

that  all  of  the 
shortly  after 
i  other  organs, 
s  a  matter  of 
hile  it  is  true 
it  is  not  to  be 

0  those  of  the 

ftbe's  heart  is 
ly- weight,  and 
;complished  in 
onsidered  that 
ig  organism  is 

md  the  actual 
r  than  in  adult 
ip  of  oxygen— 
ppear  again  as 

>,  and  is  spent 
waste;  indeed, 

1  of  all  young 
ve  loss  of  heat. 
It,  the  need  for 
nusteat  more, 
ace  of  this  fact 
its,  perish  from 
9  organizations 

e  new  environ- 
ation  is  feeble ; 
•e  is  lower ;  the 
b  is  that  newly 
irater  for  a  con- 
tout  drowning. 
y  live  on  what 
le  blood  is  ex- 
id  during  intra- 
)osed  from  the 
ie  adult.   There 


is  more  urine  passed  and  more  urea  excreted  in  proportion  to 
the  weight. 

The  lymphaiic  system,  as  a  whole,  is  more  pronounced  in 
youth.  Certain  glands,  the  functions  r*  which  are  not  well 
understood,  for  which  reason  we  have  t.  ight  it  well  to  pass 
them  over  entirely,  are  at  their  highest  development  during 
infantile  life,  as  the  thymus  and  thyroid.  These  atrophy  as 
puberty  approaches,  especially  the  thymus  gland. 

The  prominence  of  the  lymphatic  system  harmonizes  with 
what  we  know  of  the  functions  of  the  colorless  corpuscles  of 
the  blood  in  the  work  of  building  up  tissues.  They  may  be  re- 
garded as  remnants  of  embryonic  life,  undifferentiated  cells 
awaiting  their  opportunity  to  develop,  though  we  do  not,  of 
course,  mean  to  affirm  that  in  the  blood  and  elsewhere  they 
have  no  other  functions ;  in  fact,  it  has  been  shown  that  in  the 
alimentary  tract  they  are  porters  of  digestive  products  (fat, 
etc.) ;  and  they  also  likely  play  an  imi)ortant  part  as  scavengers 
and  as  guardians  of  the  nobler  cells  against  micro-organisms, 
etc. 

DentitioiL — The  change  in  the  metabolic  powers  of  the  ani- 
mal is  foreshadowed  by  the  gradual  appearance  of  teeth  for  the 
preparation  of  a  more  solid  food  to  meet  the  altered  wants  of 
the  economy. 

The  first  appearance  of  teeth  is  in  the  upper  jaw,  the  two 
central  incisors,  soon  to  be  followed  by  the  corresponding  ones 
of  the  lower  jaw.  This  is  at  about  the  seventh  or  eighth 
month,  to  be  succeeded  by  the  lateral  incisors  a  couple  of 
months  later ;  the  first  molars  about  the  end  of  the  first  year  of 
life;  the  canines  (eye-teeth)  half  a  year  later ;  and  the  whole  of 
the  temporary  set  before  the  second  year  is  completed. 

The  permanent  teeth  replace  the  milk-teeth  very  gradually, 
and  are  thus  adapted  to  the  growing  jaws.  The  new  dentition 
begins  to  appear  about  the  sixth  year,  and  may  continue  for 
six  or  eight  years.  The  last  molar  (wisdom  tooth)  appears  very 
late,  between  the  seventeenth  and  the  twenty-fifth  year.  It  is 
noteworthy  that  this  tooth  seems  to  be  more  and  more  delayed, 
and  often  never  appears  at  all,  which  may  be  said  of  some 
others,  especially  the  lateral  incisors ;  so  that  it  looks  as  if,  as 
civilization  progressed,  the  jaw  were  becoming  smaller  and  the 
teeth  suffering  atrophy.  Both  the  teeth  and  the  hair  are  epi- 
dermic structures,  and  their  defective  growth  at  the  present 
time  in  so  many  individuals  raises  suggestive  questions.  The 
face  of  civilized  man  seems  also  to  be  getting  smaller  relatively 


669 


ANIMAL  PHTSIOLOOT. 


to  the  head.    Is  this  an  example  of  correlated  growth,  to  be 
explained  by  the  predominance  of  the  cerebrum  ? 

Vtrrooi  Syitom. — The  nervous  system,  like  all  the  others,  is 
highly  sensitive;  it  reacts  powerfully  to  moderate  stimuli;  its 
equilibrium  is  more  readily  disturbed  than  that  of  any  other ; 
and,  since  to  it  belongs  the  work  of  guiding  the  metabolic  pro- 
cesses of  the  various  tissues,  this  peculiarity  explains  the  readi- 
ness with  which  the  health  of  the  infant  can  be  deranged  or 
restored.  Hence  it  follows  that  a  prognosis  in  the  case  of  in- 
fants must  be  unusually  guarded. 

As  has  been  already  indicated,  the  cortical  cells  of  the  cere- 
brum, and  other  parts  of  the  brain,  are  but  indifferently  devel- 
oped at  birth ;  so  that  stimulation  of  the  cerebral  surface  in 
young  animals  (though  there  is  great  difference  in  this  respect) 
must  not  be  expected  to  give  precisely  the  same  results  as  in 
adults. 

From  the  share  that  we  now  know  the  cortex  of  the  cere- 
brum to  take  in  the  elaboration  of  probably  all  sensory  im- 
pulses, it  follows  that  in  the  infaiii<.  all  of  the  senses  must  be  to 
a  certain  extent  imperfect,  even  &EWuming  that  the  peripheral 
mechanisms  are  as  perfect  fun  3tioually  as  in  the  adult,  which 

is  not  likely. 

In  some  respects,  however,  the  eye  of  the  infant  is  more 
perfect.  Its  power  of  accommodation  for  near  objects  is  won- 
derful, while  at  a  very  early  age  the  pupil  acts  perfectly,  and 
binocular  vision  is  established. 

Touch  is  fairly  developed,  and  probably  also  taste  and 
smell ;  though  as  tc  the  last  two  there  is  more  doubt.  On  the 
other  hand,  hearing  in  the  infant  is  very  imperfect ;  power  to 
discriminate  between  the  pitch  and  quality  of  sounds  is  rudi- 
mentary ;  while  ajypreciation  of  direction,  which  is  largely  the 
result  of  experience,  is  necessarily  of  the  crudest. 

It  is  doubtful  if  the  middle  ear  is  properly  pervious  to  air, 
on  which  its  functioning  depends  g^roatly  for  some  time  after 
birth.  But  certainly,  as  regards  the  processes  of  the  peripheral 
mechanisms  of  the  senses,  the  child  that  has  passed  the  years 
of  infancy  knows  a  perfection,  to  which  he  becomes  more  and 
more  a  stranger  as  years  pass  by.  Later  he  will,  in  consequence 
of  accumulating  experience,  xnake  more  out  of  his  sensory 
data;  his  cerebral  cortex  will  be  more  developed,  both  strnct- 
urally  and  functionally. 

Maturitf  (Pabatj).— Though  most  of  the  organs  of  the  body 
continue  to  improve,  and  certainly  the  organism,  as  a  whol^ 


1 


MAN  CONSIDERED  PHTBIOT    •OICA.LLT. 


wt 


growth,  to  be 

the  others,  is 
»  stimuli;  its 
of  any  other; 
netabolic  pro- 
ains  the  readi- 
e  deranged  or 
he  case  of  in- 

Us  of  the  cere- 
Ferently  devel- 
ral  surface  in 
n  this  respect) 
le  results  as  in 

of  the  cere- 
11  sensory  im- 
ses  must  be  to 
the  peripheral 
e  adult,  which 

infant  is  more 

objects  is  won- 

perfectly,  and 

dso  taste  and 
loubt.  On  the 
feet;  power  to 
lounds  is  rudi- 
i  is  largely  the 
t. 

lervions  to  air, 
>me  time  after 
the  peripheral 
«8ed  the  years 
omes  more  and 
in  consequence 
of  his  sensory 
d,  both  strnct- 

018  of  the  body 
m,  as  a  wholes 


up  to  about  the  fortieth  year  of  life  <  iater,  pub  ty  is  tltal 
period  of  life  which  is  most  remarkable  iur  sudden,  ^.  riknfi: 
velopment.  While  this  is  in  some  respects  most  pronouni  > 
the  sexual  organs  and  related  parts,  as  the  pelvis  and  mamir  y 
glands  of  the  female,  yet  a  whole  host  of  other  changes  ^e 
place  simultaneously,  in  such  a  way  as  to  leave  no  doubt  .  at 
they  are  related  to  those  of  the  sexual  organs.  Not  only  the 
characteristic  form  of  the  body,  but  the  psychic  peculiarities  of 
the  sexes,  appear  and  become  fully  established  with  an  extraor- 
dinary rapidity. 

There  is,  therefore,  no  period  of  life  fraught  with  so  much 
of  developmental  good  or  ill  as  puberty.  A  host  of  diseases 
may  now  show  themselves,  according  to  the  laws  of  heredity, 
as  a  result  of  deficient  resistance,  etc. 

The  8«iM. — ^While  the  differentiation  of  sex  becomes  greatly 
more  pronounced  at  puberty,  there  are  decided  differences  be- 
tween the  male  and  female  infant.  The  male  from  birth  is  the 
taller  and  the  heavier.  This  inequality  is  maintained  in  adult 
life.  The  average  woman  is  shorter  and  lighter  than  the  man ; 
her  muscular  and  bony  systems  are  less  developed,  both  abso- 
lutely and  relatively;  her  brain  is  some  ounces  lighter;  her 
blood  is  poorer  in  hsemoglobin,  of  lighter  specific  gravity,  and, 
as  a  whole,  less  in  quantity.  Woman's  metabolism,  if  we  may 
judge  by  the  income  and  expenditure,  is  both  absolutely  and 
relatively  less.  Man's  physical  strength  is  nearly  double  that 
of  woman. 

These  facts  have  an  important  bearing  on  some  of  the  burn- 
ing questions  of  the  day.  There  are,  it  will  be  seen,  deep-lying 
differences  between  the  sexes,  \vhich  can  not  be  ignored  in  our 
education  and  civilization  generally,  without  running  counter 
to  that  sexual  differentiation  which  Nature,  through  long  ages, 
has  been  bringing  toward  higher  and  higher  development. 

(Hd  Agt. — From  middle  life  onward,  in  most  persons,  there 
is  a  gradual  process  of  deterioration  going  on  in  every  tissue. 
Elasticity  diminishes  and  rigidity  of  tissues  becomes  more  and 
more  marked.  The  arteries  undergo  changes  which,  whether 
fatty  or  calcareous,  greatly  impair  their  usefulness ;  the  carti- 
lages of  the  ribs  and  other  parts  tend  to  become  calcareous,  so 
that  the  chest-walls  possess  less  of  elasticity ;  this,  combined 
with  a  general  impairment  of  muscular  power,  lessens  the 
cai>ability  of  thoracic  movement.  Protoplasm  everywhere  has 
less  vital  potential,  so  to  speak ;  hence  with  the  approach  of  old 
age  we  often  find  adipose  tissue  in  excess.    It  becomes  a  bur- 


668 


ANIMAL  PHYSIOLOOT. 


den  to  an  already  weakened  organism.  Nervous  discharges 
tend  more  and  more  to  be  slow,  weak,  and  to  take  the  lines 
fixed  by  long  usage ;  hence,  perhaps,  that  undue  conservation 
of  mind  common  to  the  old ;  that  lack  of  enterprise,  which  is 
strengthened  by  the  consciousness  of  inability,  physical  and 
mental,  for  the  strain  of  new  undertakings.  Hence  also  the 
natural  failure  of  acquiring  power  and  the  memory.  The 
judgment,  dependent  as  it  is  on  accumulating  experience,  im- 
proves. With  extreme  old  age  there  is  a  reversion  to  the 
infantile  condition,  marked  by  irritability  of  tissues,  weak- 
ness,  etc. 

The  laws  of  habit  and  rhythm  are  illustrated  abundantly 
in  the  subjects  we  have  been  considering.  Rhythm  seems  to 
be  a  sort  of  key-note  to  the  interpretation  of  the  universe ;  but 
since  we  have  frequently  referred  to  this  subject  throughout 
the  volume,  it  will  not  be  further  dwelt  upon  now. 

OompantiTa.  —  All  mammals  have  their  periods  of  rapid 
growth,  slower  decay,  and  death.  Their  growth  is  usually 
more  rapid  than  man's,  and  as  their  whole  lives  are  shorter, 
with  few  exceptions,  their  rate  of  decay  is  faster.  There  are 
great  differences  between  various  mammals  in  their  degree  of 
development  at  birth.  Among  some  (the  marsupials)  they 
separate  from  the  mother  internally,  to  become  attached  to  the 
nipples  externally  when  very  imperfectly  developed.  Though 
puppies,  kittens,  and  other  members  of  the  groups  to  which 
they  belong  (comivora)  are  bom  with  the  eyes  unopened,  no 
mammal  is  so  helpless  as  the  human  infant  when  ushered  into 
the  world.  Most  animals  learn  the  use  of  their  muscles,  and  to 
provide  for  themselves  in  a  very  short  period.  Slowness  of 
development  is,  however,  even  among  the  lower  animals,  fre- 
quently associated  with  the  attainment  of  an  ultimately  higher 
functional  status,  and  the  precocious  child  should  be  the  object 
of  some  anxiety.  It  may  develop  into  a  prodigy  of  talent,  rise 
little  above  mediocrity,  or  become  the  subject  of  some  serious 
or  fatal  form  of  disease. 

It  is  important  to  recognize  that  sexual  maturity,  in  the 
sense  of  ability  to  produce  ripe  ova  and  spermatozoa,  does  not 
correspond  with  the  full  development  of  the  animal ;  so  that  it 
may  be  as  unscientific  to  breed  together  animals  that  are  very 
young  as  those  that  are  deca3ring  from  age.  Especially  is  it 
undesirable  to  mate  two  very  young  or  very  old  animals.  Such 
a  principle  applies,  of  course,  also  to  man. 

DMth. — If  the  continuance  of  life  is  dependent  on  the  cease- 


MAN  CONSIDERED  PHYSIOLOGICALLY. 


669 


as  discharges 
ake  the  lines 
conservation 
irise,  which  is 
physical  and 
ence  also  the 
lemory.  The 
xperience,  im- 
ersion  to  the 
issues,  weak- 

ed  abundantly 
rthm  geems  to 
universe;  but 
ct  throughout 
w. 

iods  of  rapid 
irth  is  usually 
as  are  shorter, 
er.  There  are 
Iheir  degree  of 
Lrsupials)  they 
Attached  to  the 
oped.  Though 
>oups  to  which 
8  unopened,  no 
m  ushered  into 
muscles,  and  to 
..  Slowness  of 
)r  animals,  f  re- 
bimately  higher 
id  be  the  object 
f  of  talent,  rise 
»f  some  serious 


less  adaptation  of  internal  to  external  conditions,  it  becomes 
clear  that  death  may  be  said  to  be  ever  imminent ;  and  in  the 
highest  mammals  the  vital  organism  is  so  complex  and  so 
delicately  balanced,  that  it  is  marvelous  that  life  lasts  so  long 
as  it  does.  Few  animals  perish  from  simple  decay  leading  to  a 
gradual  slowing  of  the  vital  machinery,  down  to  zero,  so  to 
speak ;  but  when  death  is  not  due  to  violence,  as  it  frequently 
is,  it  rather  arises  from  some  Essential  part  getting  out  of  gear, 
either  directly  or  indirectly.  So  great  is  the  need  of  a  constant 
supply  of  free  oxygen  in  the  mammal,  that  an  arrest  of  the 
respiration  always  implies  a  stoppage  of  the  circulation.  These 
results  may  be  brought  about  by  the  direct  action  of  poisoned 
blood  on  the  heart,  or  on  the  nervous  centers  presiding  over 
lungs,  heart,  and  other  organs.  Death  may  then  be  due  to 
central  influences,  though  finally  the  arrest  of  the  circulation 
is  the  real  proximate  cause.  When  the  circulation  is  so  ar- 
rested that  it  can  not  be  started  again,  somatic  or  body  death 
must  follow,  which  is  to  be  distinguished  from  the  death  of 
the  individual  tissues. 

Somatic  death  marks  the  first  stage  of  the  return  of  a  vital 
organism  toward  the  inorganic  world,  whence  it  was,  in  a 
sense,  derived.  That  molecular  arrangement  or  movement 
peculiar  to  living  things  once  being  permanently  deranged, 
its  resolution  into  the  less  complex  forms  of  the  inorganic 
compounds  speedily  follows,  though  the  rate  will  depend  much 
upon  circumstances  in  any  individual  case.  Life  is  much 
more  of  a  mystery  than  death.  Physiology  attempts  to  de- 
fine the  conditions  under  which  life  exists,  but  can  not  explain 
life  itself.    Will  it  ever  lift  the  veil  ? 


laturity,  in  the 
btozoa,  does  not 
imal;  so  that  it 
B  that  are  very 
Especially  is  it 
animals.    Such 


i 


at  on  the  cease- 


Va«. 


APPENDIX. 


ANIMAL  CHEMISTKT. 

An  attempt  will  be  made  in  this  chafiter  to  give  a  brief  a4KX>unt  of 
the  principal  substances  entering  into  or  derivable  from  the  mammalian 
body,  or  resulting  from  its  metabolism.  We  may  repeat  that,  inasmuch 
as  chemical  treatment  kills  living  organisms,  we  can  only  know  the 
chemical  constitution  of  the  dead  body. 

The  cells  and  tissues  of  the  body  of  a  mammal  are  made  up  of  proto- 
plasm, which  belongs  to  that  large  class  of  bodies  known  as  proteids. 
However,  it  is  seldom,  if  ever,  that  pure  protoplasm  is  found,  for  even 
in  the  youngest  cells  and  in  imicellular  animals  and  plants  this  sub- 
sti^Qce  usually  contains  some  representatives  of  the  class  of  bodies  known 
as  carbohydrates  and  fats.  Protoplasm  Is,  moreover,  the  producer  or 
builder  of  both  fats  and  carbohydi-ates,  as  has  been  already  learned.  In 
one  sense  all  the  chemistry  of  the  body  is  the  chemistry  of  protoplasm, 
in  that  it  is  either  by  one  or  other  phase  of  the  metabolism  of  cells  that 
the  various  secretions,  excretions,  and  reserve  products  of  cells  arise. 
We  have  already  considered  this  aspect  of  the  subject  in  connection 
with  the  treatment  of  the  metabolism  of  the  animal  body,  and  shall 
now  direct  attention  in  more  detail  to  certain  chemical  facta,  groupings, 
and  principles,  largely  with  the  purpose  of  illustrating  the  resemblances 
between  the  products  of  our  laboratories  and  of  our  bodies.  At  the 
same  time  it  is  to  be  borne  in  mind,  as  we  have  often  remarked  in  the 
main  body  of  the  work,  that  we  are  generally  unable  to  say  whether  the 
syntheses  and  analyses  of  the  body  resemble  those  made  by  the  chemist 
in  the  laboratory  or  not  Indeed,  the  whole  subject,  from  this  point  of 
view,  is  as  yet  in  a  very  crude  condition. 


PROTEIDa 

These  include  a  large  class  of  bodies  as  yet  very  imperfectly  under- 
stood chemically.  According  to  Hoppe-Seyler,  the  following  percentage 
composition  may  be  assigned  to  them  : 

O  N  HO  8 

90D-M-5.  W-S-17-0,  •♦-T-S,  51-»^'6,  0»-«U 

Usually  on  ignition  a  very  small  quantity  of  ash  remains. 


672 


ANIMAL  PHTSIOLOOT. 


Proteids  are  amorphous ;  insoluble  in  alcohol  and  ether ;  some  of 
them  soluble  in  water ;  soluble  with  change  of  constitution  in  strong 
acids  and  alkalies,  and  laevo-rotatory. 

T«ftS  for  Froteids.— 1.  With  Millon's  reagent  (mercury  dissolved  in 
its  own  weig]'t  of  nitric  acid,  and  the  solution  diluted  with  twice  its 
volume  of  water)  a  precipitate,  rendered  red  by  boiling.  2.  Heated 
with  strong  nitric  acid,  they  become  yellow.  On  adding  ammonia  or 
caustic  soda,  or  potash,  the  yellow  is  replaced  by  an  orange  {xantho- 
proteic reaction).  3.  On  adding  caustic  alkali  and  a  drop  or  two  of 
copper  sulphate,  a  violet  color  is  produced,  which  can  be  deepened  by 
boiling.  4.  To  the  suspected  fluid  add  enough  acetic  acid  to  render  it 
decidedly  acid,  and  then  a  few  drops  of  potassium  ferrocyanide.  A 
white  precipitate  indicates  that  proteids  are  present.  6.  To  the  fluid 
rendered  decidedly  acid,  add  a  strong  solution  of  sodium  sulphate  and 
boil.    If  a  precipitate  falls,  some  proteid  was  present 

The  first  three  tests  are  the  most  reliable,  and  apply  to  all  classes  of 
proteids. 

PBOPBBTIES  and  CliABSmOATION  OF  THK  PBOTEIDB. 

I.  Native  AUmnUns. 

These  occur  naturally  in  the  tissues  and  fluids  of  the  body.  They 
are  soluble  in  water,  are  not  thrown  down  by  the  alkaline  carbonates, 
by  sodium  chloride,  or  by  very  dilute  acids.  Their  ccagulation-point 
lies  below  70°  C.  They  may  be  dried  with  change  of  color  to  a  pale 
yellow,  but  remain  soluble. 

1.  Sgg*Albllllli]L— This  may  be  obtained  for  purposes  of  experiment 
by  cutting  up  raw  white  of  egg  with  scissors,  diluting  with  water,  strain- 
ing through  cotton,  a?  d  afterward  through  filter-paper.  The  resulting 
fluid  is  almost  colorless  at  flrst,  but  on  standing  darkenJs  gradually.  It 
may  be  precipitated  by  strong  alcohol,  which  does  not  seem  to  alt«r 
its  chemical  constitution,  or  by  strong  acids,  when  a  great  chemical 
change  takes  place.  Various,  mineral  salts,  as  silver  nitrate,  mercuric 
chloride,  etc.,  form  with  albumin  insoluble  compounds.  Whether  albu- 
min ever  e^dsts  entirely  free  from  combination  with  salts  in  the  animal 
body  is  a  question ;  probably  not 

By  the  addition  of  strong  acetic  acid  or  caustic  alkali,  a  clear,  jelly- 
like mass  results,  being,  in  the  flnt  case,  acid-albumin,  and  in  tLe  second 
alkali-albumm.    It  is  laevo-rotatory  to  the  extent  of  SS-S"  (— 86-5"). 

2.  BemmnAnramin.— This  compound  greatly  resembles  th.e  foregoing, 
but  may  be  distinguished  by  the  following  characteristics:  (a)  Serum- 
albumin  is  not  like  egg-albumin,  coagulated  by  ether,  (b)  Serum-albu- 
min is  less  readily  coagulated  by  strong  hydrocUorio  add,  and  any  pre- 
cipitate formed  is  easily  diMwlved  by  excess  of  add,  in  which  respects  it 
is  the  reverse  of  ^^g^lbumin.  (o)  Coagulated  serum-albumin  is  readily 
soluble  in  strong  nitric  acid,  the  reverse  holding  for  egg^lbumin.  (d) 
The  specific  rotation  of  egg^lbumin  is  —85-5° ;  of  serum-albumin,  —56°. 
(e)  Serum-albumin  occun  in  blood,  lymph,  chyle,  milk,  and  pathological 


her ;  some  of 
ion  in  strong 

y  dissolved  in 
vrith  twice  its 
I.  2.  Heated 
f  ammonia  or 
uige  {xantho- 
rop  or  two  of 
e  deepened  by 
id  to  render  it 
rocyanide.  A 
.  To  the  fluid 
I  sulphate  and 

o  all  classes  of 


XIDS. 


e  body.  They 
ine  carbonates, 
Bgulation-point 
color  to  a  pale 

I  of  experiment 
b.  water,  strun- 
The  resulting 
i  gradually.  It 
t  seem  to  alter 
great  chemical 
itrate,  mercuric 
Whether  albu- 
ts  in  the  animal 

li,  a  dear,  jelly- 
id  in  tLe  second 

>s  thp  foregoing, 
tics:  (o)  Serum- 
(6)  Serum-albu- 
i5id,andanypre- 
trhich  respects  it 
bumin  is  readily 
(g-albumin.  (d) 
t-albumin,  —66°. 
uid  pathological 


APPENDIX. 


678 


transudations  ;  and,  when  injected  into  the  blood,  doea  not  reappear  in 
Ihe  urine,  while  the  injection  of  egg-|||bumin  is  followed  by  its  appear- 
ance in  the  urine  apparently  unaltered.  In  fact,  this  form  of  proteid 
constitutes  a  great  part  of  the  "albumin"  of  the  urine  of  such  signifi- 
cance in  pathological  conditions.  However,  increasing  knowledge  seems 
to  point  to  the  "albumin  "  of  the  urine,  like  many  other  forms  of  pro- 
teid, being  more  complex  than  was  once  supposed. 

II.  Derived  Albumins  (Albuminates). 

1.  Aeid-AIbninill.— This  may  be  formed  by  the  addition  of  a  strong 
acid  to  egg-albumin,  or,  more  gradually,  by  heating  a  weaker  solution 
of  egg-albumin  with  an  extremely  dilute  acid. 

Acid-albumin  is  characterized  by  non-precipitation  on  boiling,  com- 
plete precipitation  on  the  addition  of  a  dilute  alkali  to  the  point  of  neu- 
tralization—that is,  acid-albumin  is  insoluble  in  water  or  such  like  neu- 
tral liquids.    It  is  soluble  in  an  excess  of  acid  or  of  alkali. 

By  treating  finely  minced  muscle  with  a  weak  acid,  a  substance  is 
obtained  not  readily  distinguishable  from  acid-albumin,  but  known  as 
syntonin.  This  is  probably  not  identical  Mrith  acid-albumin  as  formed 
by  the  method  indicated  above,  though  a  distinguishing  test  of  a  wholly 
satisfactory  character  is  not  known.  Neither  this  substance  nor  acid- 
albumin  coagulates  on  boiling,  in  which  it  bears  a  resemblance  to  pep- 
tone. The  parapeptone  of  digestion  seems  to  be  very  similar  to  acid- , 
albumin.  A  solution  of  acid-albumin  in  acid  may  be  precipitated  by 
the  addition  of  an  excess  of  common  salt. 

2.  AlkaUfAUnuilin.— This  corresponds  to  the  fon^ing,  and  may  be 
formed  in  a  similar  way  by  the  addition  of  an  alkali  instead  of  an  acid. 
It  is  not  ooagulable  on  boiling,  and  is  precipitated  by  dilute  acid,  in 
excess  of  which  and  of  alkali  it  is  soluble,  but,  like  acid-albumin,  is  in- 
soluble in  water  and  solution  of  neutral  salts.  The  specific  rotation 
varies  with  the  mode  of  preparation,  from  which,  as  well  as  on  other 
gvounds,  it  is  more  than  likely  that  there  are  different  kinds  of  alkali- 
albumin.  It  is  highly  probable  that  acid-albumin  and  alkali-albumin 
are  combinations  of  an  acid  or  an  alkali,  as  the  case  may  be,  with  albu- 
min, and  that  the  neutralization  precipitate  is  not  in  itself  either  one  or 
the  other. 

3.  CMein.— This  substance  is  the  proteid  most  characteristic  of  milk, 
from  which  it  may  be  obtained  by  dilution  ten  to  fifteen  times  with  water, 
adding  acetic  acid  till  a  precipitate  begins  to  form,  and  then  sending  a 
current  of  CX>t  through  the  fluid.  After  standing,  the  precipitate  may 
be  collected  in  a  filter.  It  is  freed  from  salts,  sugar,  fat,  etc.,  by  first 
washing  with  water  and  then  with  alcohol  and  ether. 

It  is  so  like  alkali-albttmin  that  there  is  no  agreement  yet  as  to  the 
differences  between  them.  However,  the  presence  in  milk  of  potassium 
phosphate  modifies  the  reactions  of  casein  in  this  fiuid.  It  may  be  precipi- 
tated also  by  adding  magnesium  sulphate  to  saturation  to  milk.  This  pre- 
cipitate is,  however,  easily  soluble  in  water.  The  specific  rotation  of  casein, 
when  in  solution  in  water  is  —80°,  but  in  other  solutions  is  different. 
48 


674 


ANIMAL  PHYSIOLOGY. 


m.  Globulins. 

This  class  of  bodies  is  characterized  by  being  insoluble  in  water,  solu- 
ble in  dilute  saline  solutions  (especially  sodium  chloride) ;  soluble  in 
dilute  acids  and  alkalies,  when  they  are  transformed  into  acid-albumin 
and  alkali-albimiin  respectively.  Most  of  the  globulins  are  preoipitxted 
by  saturation  with  solid  sodium  chloride. 

1.  Globulin  (Crystallin).— When  the  crystalline  lens  of  the  eye  is 
rubbed  up  with  fine  sand  and  extracted  with  water,  upon  filtration  and 
passing  a  stream  of  carbon  dioxide  through  the  filtrate,  a  precipitation 
of  globulin  is  obtained.  Though  strongly  resembling  paraglobulin  and 
fibrinogen,  it  is  not  known  to  favor  fibrin-formation. 

2.  FangloboUll  (Fibrinopla«tin).— This  body  may  be  obtained  from 
blood-serum  by  passing  through  it  a  current  of  carbonic  anhydride, 
when  a  flocculent  precipitate  falls,  which  later  becomes  very  finely  gran- 
ular, and  may  be  separated  by  filtration.  Addition  of  solid  sodium 
chloride  precipitates  this  substance  only  in  part.  It  is  very  readily 
changed  into  alkali-albumin,  and  still  more  so  to  acid-albumin,  by  addi- 
tion of  dilute  alkalies  or  acids.  This  body  is  not  easUy  precipitated  by 
alcohol.    Its  coagulation-point  is  about  70°  C. 

Paraglobulin  has  been  found  in  blood-serum,  lymph,  chyle,  serous 
fiuids,  the  aqueous  humor,  the  cornea,  connective  tissue,  and  in  the  pale 
and  colored  corpuscles.    It  occasionally  appears  in  urine  as  a  patho- 

'logical  product.  ,  .    ,.     •  * 

3  MwillOgeil.— Wliile  greatly  resembling  paraglobulm  m  most 
characteristics,  the  coagulation-pomt  is  different,  being  62"  to  55°  when 
in  solution  in  dilute  sodium  chloride.  It  is  not  so  readily  precipitated 
from  diluted  solutions  as  the  body  previously  described,  and  is  viscous 

rather  than  granular.  x-        xu     „». 

It  may  be  obtained  from  blood-plasma  by  special  preaiutions^  though 
more  readily  from  hydrocele-fluid.  Fibrinogen  occurs  m  blood,  chyle, 
serous  fiuid^  and  numerous  transudations.  It  has  been  considered  by 
many  observers  to  be  essential  m  the  formation  of  flbnn. 

4  MyoHiil,  as  its  name  implies,  is  derivable  from  musde-plasma,  and 
may  be  regarded  as  the  latter  substance  in  an  altered  f  onn.  It  may  be 
pre'pared  from  washed  muscle,  by  treatment  with  a  ten-peiM^ent  solution 
of  common  salt,  and  dropping  the  viscid  product  slowly  mto  distilled 
water,  when  it  falls  as  a  flocculent,  whitish  precipitate.  It  is  readay  con- 
verted into  syntonin  (a  form  of  acid-albumin,  as  has  been  pomt^l  out) 
by  acids,  and  into  alkaU-albumin  by  alkalies.  In  very  w^k  acids  and 
alkalies  it  is  soluble  without  conversion  into  a  different  substance.  The 
coagulation-point  of  myosin  is  low,  66°  to  60°  C.  . 

6  Vitellln.-Thb  body,  probably  united  witii  lecithm,  is  the  chief 
prot^id  constituent  of  the  yelk  of  egg,  from  which  it  is  usually  prepared. 
It  differs  from  most  of  the  globulms  in  not  being  precipitated  f rom  ite 
solutions  by  sodium  chloride.    The  coagukition-point  Ues  between  70 

and  80°  0.  ,    .  _j  j       ♦».„ 

6.  Olobln  is  a  doubtful  member  of  this  ckss.    It  is  regarded  as  the 


.!!MLlE,it'yiJ.l' 


'  -^■i4JJ',gJ'."L 


APPENDIX. 


676 


in  water,  boIu- 
le) ;  soluble  in 

0  acid-albumin 
ire  preoipitxted 

;  of  the  eye  is 

1  filtration  and 
a  precipitation 
,ra£ri6bulin  and 

obtained  from 
nic  anhydride, 
sry  finely  gran- 
[  solid  sodium 
is  very  readily 
lumin,  by  addi- 
precipitated  by 

h,  chyle,  serous 
and  in  the  pale 
ine  as  a  patho- 

tbulin  in  most 
62"  to  55°  when 
lily  precipitated 
,  and  is  viscous 

autioos,  though 
m  blood,  chyle, 
I  considered  by 
I. 

scle-plasma,  and 
rm.  It  may  be 
[ler-cent  solution 
ly  into  distilled 
It  is  readily  con- 
en  pointed  out) 
weak  acids  and 
substance.    The 

hui,  is  the  chief 
isually  prepared, 
ipitated  from  its 
lies  between  70° 

regarded  as  the 


proteid  residue  of  heemoglobin.  It  is  not  easily  soluble  in  dilute  acids 
or  sodium  chloride,  hence  it  is  with  hesitation  ranked  with  the  other 
globulins. 

IV.  Fibrin. 

This  body  has  peculiarities  which  warrant,  in  the  present  state  of  our 
knowledge,  its  separation  from  the  foregoing  and  placing  it  in  a  sepa- 
rate division.  It  is  insoluble  in  water  and  dilute  solutions  of  sodium 
chloride ;  dissolved  only  with  difficulty  in  concentrated  neutral  saline 
solutions,  and  in  dilute  acids  and  alkalies. 

Fibrin  is  highly  elastic.  It  always  swells  under  the  action  of  weak 
(1  to  6  per  cent)  hydrochloric  acid.  But  continued  action  of  the  acid 
changes  the  fibrin  to  syntonin.  Heat  hastens  the  process.  By  the  ac- 
tion of  alkalies,  especially  when  aided  by  warming,  fibrin  is  converted 
into  alkali-albumin.  By  the  prolonged  action  of  solutions  of  sodium 
chloride  (10  per  cent),  sodium  sulphate,  etc.,  conversion  into  a  substance 
very  like  myosin  or  globulin  is  effected.  Myosin  may  be  regarded  as 
an  intermediate  product,  lying  between  globulin  and  fibrin.  ^This  be- 
comes clear  when  comparing  their  respective  solubilities  in  a  ten-per- 
cent solution  of  sodium  chloride.  Fibrin  and  myosin,  it  will  be  re- 
membered, are  both  the  products  of  coagulation  processes.  The  highly 
filamentous  character  of  fibrin  distinguishes  it  physically  from  all  other 
proteids. 

V.  Coagulated  Proteida. 

This  class  of  bodies  may  be  obtained  from  a  variety  of  others  by  the 
use  of  heat,  alcohol,  acids,  etc.  By  heating  to  about  70°  C,  solutions  of 
egg-albumin,  serum-albumin,  and  globulins  are  coagulated.  Precipi- 
tated acid-albunun  and  alkali-albumin,  and  fibrin  in  solution  in  salines, 
are  converted  into  coagulated  proteids  by  boiling.  The  digestive  juices 
act  readily  on  them,  converting  them  finally  into  peptones. 

VI.  P^tonea. 

Peptones  are  proteids  which,  though  possessing  little  absolute  difFa- 
sibility,  as  compared  with  solutions  of  ordinary  salts,  yet  pass  through 
animal  membranes  with  much  greater  readiness  than  any  other  proteids. 
Also,  unlike  most  other  proteids,  they  are  not  coagulated  by  boiling. 
They  are  not  precipitated  by  cupric  sulphate,  ferric  chloride,  nor  usually 
by  potassium  ferrocyanide  and  acetic  acid.  Though  precipitated  by 
alcohol  from  solution  in  water,  they  do  not  undergo  a  true  coagulation, 
even  after  standing  long  under  this  liquid. 

Peptones  are  coagulated  by  chlorine,  iodine,  tannin,  the  nitrates  of 
mercury  and  silver,  mercuric  chloride,  and  the  lead  acetates.  A  mere 
trace  of  cuprio  sulphate  to  which  a  strong  solution  of  caustic  alkali  has 
been  added,  introduced  into  a  solution  of  peptones,  gives  rise  to  a  red 
(pink)  color.  If  more  than  a  trace  of  the  copper  salt  be  added,  the  u«ual 
proteid  reaction  results. 

Peptones  may  be  formed  through  the  action  of  dilute  or  stronger 
acids  at  medium  temperatures,  or  by  the  action  of  distilled  water  heated 


676 


ANIMAL  PHYSIOLOGY. 


above  the  boiling-point  under  pressure  in  a  special  apparatus.  The  usual 
SXd  ^  howeveV.  by  the  action  of  gastric  or  pancreatic  juice  on  white 

^'Tsi^t^^SrVrS::^  that  the  bodies  fonned  by  ^e  different 
methods  indicated  above  ar^  not  identical,  though  harmg  many  proper- 
tii  in  common.  Between  the  original  proteid  and  the  peptone  other 
bodies  seem  to  be  formed  either  as  by-p^tsor  ^  u^r^^os^; 
ies,  and  the  rektion  of  these  has  been  expressed  m  tabuhir  form  (Foster) 

ihuB  : 

Decompomlion  of  Pnteida  by  Digeatton. 

Albumin.  A 


Antialbumose. 


Hemialbumoee 


.|  I  Antipeptone. 


r 


Leucin.    Tyrosin, 
etc. 


Leucin.    Tyrosin, 
etc. 


e> 


Antipeptone.  Heraipeptone.  Hemineptone.    i| 


DeeomporiHon  by  Adda. 

1. 

By  -25  per  cent  HCl  at  40'  C. 

Albumin. 


Antialbumate. 
AntialDumid. 


Hemialbumose. 


Hemiiteptone,         Hemipeptoue. 


2. 


By  3  to  5  per  cent  H«S04  at  100'  C. 
Albumin. 


Antialoumid. 


Hemialbumose. 


Hemipeptone. 


1 


Hemipeptone. 


Leucin,  Tyrosin,  etc.       Leucin,  TytosJn,  etc. 

It  will  be  observed  that  antialbumose  and  »»«™i»>^«'"'««  *~  "^f^ 
mediate  p«>ducte  of  digestion,  and  they  occur  in  both  peptic  and  tryptic 

^**^Sbumate  takes  the  place  of  antialbumose  when  albmninte  di- 
aested  with  dilute  hydrochloric  acid  at  40°  C,  or  when  pepUc  digestK,n 
K'or^ally  active.  It  can  be  changed  into  peptone  by  tryp«r^  but 
not  by  pepsinfand  seems  to  correspond  with  the  parapeptone  of  some 
;lo«Tri8;ner).    The  table  is  also  meant  to  indicate  that  antmlbu- 


APPENDIX. 


677 


tus.  The  tisual 
:  juice  on  white 

by  the  different 
g  many  proper- 
9  peptone  other 
itennediate  bod- 
uf  form  (Foster) 


.4  ' 


». 


emipeptone.    ^  "§ 


icin.    Tyrosin, 
etc. 


imose. 


HemipiBptoue. 


w. 


Hemipeptone. 

cin,  Tyft)8Jn,  etc. 

ibumose  are  inter- 
peptic  and  tryptic 

len  albumin  is  di- 
m.  peptic  digestion 
ne  by  trypsin,  but 
•aj)eptone  of  some 
»te  that  antialbtt- 


mose  and  hemialbumose  both  result  from  peptic  digestion,  and  it  is 
assumed  that  these  both  split  up  into  two  molecules  of  antipeptone  or 
hemipeptone,  according  as  the  digestion  is  either  peptic  or  tiyptic.  Evi- 
dently, trypsin  carries  the  processes  much  further  than  pepsin. 

Vn.  Lardaeein  (Amyloid  Substance). 

This  body  is  not  found  in  the  tissues  in  health,  but  results  from  a 
pathological  process,  and  is  most  frequently  found  in  the  spleen,  liver, 
kidneys,  lungs,  blood-vessels,  etc.  It  consists  of  CHNO  and  a  little  sul- 
phur in  some  oxidized  form.  It  is  insoluble  in  water,  dilute  acids  and 
alkalies,  and  neutral  saline  solutions.  like  other  proteids,  it  can  be  con- 
verted into  acid-albumin  and  alkali-albumin;  but,  unlike  all  other  pro- 
teids, it  is  not  affected  by  the  digestive  juices.  It  may  be  recognized  by 
giving  a  red  color  with  iodine,  and  a  violet  or  blue  when  heated  with 
iodine  and  sulphuric  acid. 

We  are  still  in  ignorance  of  the  real  molecular  constitution  of  pro- 
teids. and  our  whole  knowledge  of  this  class  of  bodies  is  in  the  empirical 
rather  than  the  scientific  stage. 

NrntooBNOus  No»-obtbtaixiot!  Bodies  aixied  to  Proteids. 
These  bodies  resemble  each  other  much  less  than  the  proteids  proper  : 

1.  Mndn  (CHNO). 

It  is  the  characteristic  body  of  mucus,  which  abounds  in  the  bile  of 
the  gall-bladder  and  in  snails,  from  either  of  which  it  may  be  prepared. 
It  may  be  precipitated  from  its  solutions  by  alcohol,  alum,  mineral  acids, 
and  acetic  acid.  The  precipitate  is  dissolved  by  excess  of  mineral  acids, 
but  not  by  acetic  acid,  so  that  the  latter  forms  one  of  the  best  tests  for 
mucin. 

2.  dumdrin  (CHNOS). 

This  substance  may  be  extracted  from  hyaline  cartilage,  and  less 
easily  from  elastic  cartilage.  It  readily  gelatinizes  from  its  solutions  on 
standing;  is  soluble  in  hot  water,  alkalies,  and  ammonia;  insoluble  in 
cold  water.  It  is  very  doubtful  whether  chondrin  of  itself  exists  in  car- 
tilage; it  is  more  likely  an  allied  product. 

3.  CMAtin,  or  QHtia  (CHNOS). 

This  substance  may  be  obtained  by  heating  connective  tissue  for  days 
with  dilute  acetic  acid  at  about  16°,  or  by  prolonged  treatment  with 
water  under  high  pressures.  It  forms,  when  not  ^ure,  the  well-known 
"glue."  Though  swelling  in  cold  water,  it  does  not  dissolve,  but  is 
readily  soluble  in  warm  water.  It  forms  insoluble  precipitates  with  tan- 
nic acid  and  mercuric  chloride. 

4.  mMtin  (CHNO). 

This  is  one  of  the  most  insoluble  substances  derivable  from  animal 
tissues.  It,  however,  yields  to  concentrated  nitric  and  sulphuric  acids 
in  the  cold  and  to  boiling  alkalies,  and  may  be  precipitated  from  its  solu- 
tions by  tannic  *cid.  The  substance  is  best  obtained  from  the  liga- 
mentum  nuchse  of  the  ox. 


■tnritirtjtwvwnfan 


678 


ANIMAL  .PHYSIOLOGY. 


6.  Ktntin  (CHNOS). 

It  makes  up  a  large  part  of  horn,  hair,  nails,  feathers,  and  is  also  a 
highly  insoluble  body.    In  all  probability  it  is  not  a  simple  substance. 

6.  Hndein  (CHNOP). 

This  body  is  derivable  from  the  nuclei  of  cells,  from  yeast,  semen, 
and  from  the  yellow  corpuscles  of  the  yelk  of  eggs.  It  is  slightly  solu- 
ble in  water,  easily  so  in  alkalies,  though  the  solubility  changes  on  keep- 
ing. It  is  best  prepared  from  pus-corpuscles,  and  contains  a  notably 
large  quantity  of  phosphorus— nine  to  ten  per  cent 

7.  Ohitin  (CHNO). 

Though  not  occurring  in  appreciable  quantity,  at  all  events  in  the 
body  of  the  mammal,  it  makes  up  a  good  part  of  the  hard  covering  of 
insects,  crustaceans,  etc.  It  has  been  regarded  as  analogous  to  the  cellu- 
lose at  plants.  It  is  a  highly  insoluble  substance,  resisting  all  reagents 
except  strong  mineral  acids.  It  may  be  obtained  pure,  as  a  white  amor- 
phous body.  The  insolubility  of  the  above  products  as  a  class  is  remark- 
able. Most  of  them  yield  either  leucin  or  tyrosin,  or  both,  under  hydro- 
lytic  treatment.  Their  relations  are  very  ill  understood,  and  it  is  doubt- 
ful if  any  of  them  are  simple  substances,  or  exist  as  such  in  the  tissues 
from  which  they  are  extracted  with  so  much  difficulty  in  most  instances. 
No  attempt  has  been  made  to  give  the  percentage  composition  of  the 
above  bodies. 

CABBOHTDRATBa. 

Of  this  class  glycogen,  dextrose  (grape-sugar,  glucose),  maltose,  milk- 
sugar,  and  inosit  occur  normally  in  the  mammalian  body. 

The  exact  chemical  constitution  and  relations  of  the  sugars  are  still 
under  discussion  ;  we  shall,  therefore,  pass  this  subject  over  in  this  brief 
outline. 

1.  DoctroM  (grape-sugar).    CiHitOt. 

The  occurrence  of  this  body  in  the  various  fluids  and  tissues  h^  been 
already  considered. 

This  sugar  ctystallixes  from  aqueous  solutions  in  prisms,  which  may 
be  agglutinated  into  lumps,  and  is,  when  chemically  pure,  colorless, 
readily  soluble  in  warm  water,  more  slowly  soluble  in  cold  water,  spar- 
ingly soluble  in  alcohol,  and  insoluble  in  ether.  Specific  rotation, 
+  104«»— i.  e.,  dextro-rotatory  104'  for  yellow  Ught  In  the  presence  of 
yeastH»lls,  and  at  a  temperatnre  of  from  5°  to  45°  O.  (best  at  about  25°  C), 
dextrose  undergoes  the  alcoholic  fermentation.  The  reactions  may  be 
thus  expressed: 

0.H..0.  =  SC.H..OH  4-  2C0t. 

In  the  presence  of  decomposing  nitrogenous  matter,  as  the  casein  of 
milk,  the  lactic  fermentation  resolta. 
Reactions: 

(a)  CtHitOt  =  SCiHtOt. 

LMtlCMid. 

(b)  SC*H.O«  =!  C«HiOi  +  SCOt  4-  2Hi. 

Butyric  ftdd. 


T^ 


APPENDIX. 


679 


I,  and  is  also  a 
tie  substance. 

I  yeast,  semen, 
8  slightly  solu- 
anges  on  keep- 
Eiins  a  notably 


events  in  the 
ird  covering  of 
lus  to  the  eellu- 
ag  all  reagents 
I  a  white  amor- 
;lass  is  remark- 
1,  under  hydro- 
and  it  is  doubt- 
L  in  the  tissues 
most  instances, 
position  of  the 


.  maltose,  milk- 

r. 

sugars  are  still 

rer  in  this  brief 


tissues  hffii  been 

ons,  which  may 
pure,  colorless, 
old  water,  spar- 
leciflo  rotation, 
the  presence  of 
at  about  25°  C), 
aactioiu  may  be 


as  the  casein  of 


A  temperature  of  about  35»  C.  is  the  most  favorable  for  this  fermen- 
tation. Dextrose  readily  reduces  copper  salts  in  the  presence  of  caustic 
alkali. 

This  sugar  may  be  artificially  produced  by  the  action  of  dtastaae,  a 
ferment  obtained  from  malted  barley,  on  starch. 

3C.H..0i  +  H.0  =  C.tH«0..  +  C.H..O.. 
BtMxeh.  Maltose.  De«rin. 

It  may  also  be  formed  by  the  action  of  dilute  sulphuric  acid  on 
starch  It  reduces coppersalts;  is  dextro-rotatory ;  ferments  with  yeast, 
and  crystallises  in  fine  needles.  It  seems  to  be  the  principal  sugar 
formed  in  the  natural  digestive  processes. 

]Ii]k<8ligar  aactose).    C.tHt«On. 

This  form  of  sugar  is  found  in  the  mUk  of  aU  animals  normally,  and 
occasionally  in  the  urine  of  animals  during  lactation. 

It  crystallizes  in  rhombic  prisms ;  its  taste  is  slightly  "weetish ;  is 
dextro-rotatory  ;  much  less  soluble  in  water  than  <«ne-sugar.  When 
the  hictoae  of  milk  ferments;  it  breaks  up  into  alcohol  and  lactic  acid, 
hence  the  souring  of  milk.  It  reduces  solutions  of  copper  salts,  but  less 
perfectly  than  dextrose,  and  is  dextro-rotatory. 

iBOrit.    CHifO..  ^^  ,       „     , 

This  substance  has  been  obtained  sparingly  from  the  muscle^lls  of 
the  heart  and  from  some  bther  organs.  It  crystallizes  m  rhombic 
prisms;  readUy  soluble  in  water  but  insoluble  in  alcohol  and  ether.  'Hus 
sugar  has  no  specific  action  on  Ught,  and  is  susceptible  ot  the  laattc  fer- 
mentation. 

Dextrin.    C«Hi*0*. 

This  substance  may  be  formed  by  the  action  of  dilute  acids  on  starch, 
or  by  the  action  of  diastase  on  the  same  body.  It  is  strongly  dextro- 
rotatory, does  not  reduce  solutions  of  copper  salts,  gives  a  red  color 
with  iodine,  is  soluble  in  water,  and  precipitated  by  alcohpL  It  is  a 
product  of  both  artificial  and  natural  digestion. 

By  the  action  of  acids  and  ferments  on  starch,  certain  modifications 
of  dextrin  are  formed.  Of  these,  erythrodextrin  becomes  sugar  by  the 
continued  action  of  ferments.  Achroodextrin  remains  unaltered  and  is 
characterized  by  giving  no  red  color  with  iodme.  It  may  be  converted 
into  dextrose  by  boiling  with  dilute  hydrochloric_^acid. 

Olyeogen.    C«H>«Of. 

This  substance  is  pretty  widely  distributed  in  the  oi^ns  of  the  body 
especially  in  the  mammalian  foetus,  and  is  found  in  abundance  in  the 
liver  of  the  adult  in  both  vertebrates  and  invertebrates.  Olycogen  when 
pure  is  white,  amorphous,  tasteless,  easily  soluble  in  water,  insoluble  in 
alcohol  and  ether,  highly  dextro-rotatory,  and  does  not  reduce  metallic 
oxides.  It  is  changed  by  the  digestive  ferments  into  a  form  of  «ugar 
and  of  dextrin,  and  gives  a  red  (port-wine)  color  with  iodine,  which  ^s- 
appears  on  warming  but  returns  on  cooling,  by  which  latter  it  is  distin- 


MVMpUMWK'nXAM 


6S0 


ANIMAL  PHrSIOLOOr. 


guished  from  dextrin.  It  is  best  extracted  from  the  liwr,  removed  as 
Hoon  as  possible  after  killing  an  animal  and  minoed,  by  boiling  water, 
then  inuifled  and  precipitated. 

Twkidii.    CtHuO*. 

This  body  is  closely  allied  to  the  cellulose  of  plants,  and  forms  the 
greater  part  of  the  integument  of  ascidians  or  tunioites.  like  ohitin,  it  is 
extremely  insoluble. 

'"    Fats,  Fatty  Acids,  bto. 

General  formula  of  series  :  C.Hk(X  or  C.H„^,.€X)bH. 

The  fatty  acid  series  answers  to  ttie  series  of  monatomic  alcohols: 
thus,  formic  acid  corresponds  to  methyl  alcohol,  and  acetic  acid  to  ethyl 
or  ordinary  alcohol. 

C5.H«0  +  O.  =  C.H«0.  +  H.0,  or 
O.H..OH  +  O.  =  CH..OO.OH  +  H.O. 

From  which  it  appears  that  O  has  taken  the  place  of  Ht  in  the  alco- 
hol to  form  the  acid— i.  e.,  the  acid  is  an  oxidised  alcohol.  The  lowest, 
members  of  the  line  are  vob^le  liquids  with  strongly  acid  reactions. 
As  the  series  is  ascended,  fluidity  diminishes,  and  finally  the  acids  are 
solids,  greatly  resembling  the  neutral  fata  in  appearance. 

The  derivatives  of  the  fatty  acids  are  very  important  in  the  animal 
economy,  but  the  free  acids  occur  sparingly. 

PonnioMdd.    H.COtH. 

A  strongly  corrosive  liquid,  boiling  at  lOO"  C,  solidifying  at  0°,  and 
mixing  readily  with  water  and  alcohol.  It  has  been  extracted  from 
various  organs. 

Aoetie  add.    CH«.CO«H. 

An  acid  liquid  of  characteristio  odor,  boiling  at  117'  C,  solidifying  at 
5**  C.    BeadUy  miscible  with  alcohol  and  water. 

It  often  occurs  in  the  stomach,  from  fermentative  changes. 

Fropimiie  Mid.    CtH>.C99H. 

Resembles  acetic  acid,  soluble  in  water  and  boiling  at  141°  0.  It 
is  found  in  perspiration,  the  stomach,  diabetic  urine  when  ferment- 
ing, etc. ' 

Botyrifl  add.    C>Ht.COtH. 

An  oily,  colorless  liquid,  with  the  smell  of  rancid  butter,  soluble  in 
water,  alcohol,  ether  ;  and  boiling  at  162'  C. 

It  is  found  in  sweat,  faeces,  urine,  and  the  contents  of  the'  large  in- 
testine. 

▼ali^iuiie  aeid.    C.H..CO.H. 

An  oily  liquid  of  strong  smell  and  taste,  soluble  in  water,  and  more 
so  in  alcohol  and  ether.  It  is  found  in  solid  excrement  In  fatty  de- 
generation of  the  liver  it  may  occur  in  the  urine,  as  a  result  of  the 
decomposition  of  leucin,  which  appears  in  abundance  in  the  urine  in 
the  above  disease. 


DUIiill-llMIIW'JIWllfW — !-»;WTO«ww» 


PWlHI'Ulil-<i)l*^Will»miLil(«i*lil.i</»!« 


APPENDIX. 


est 


pr,  removed  as 
boiling  water, 


uid  fomu  the 
ikechitiii,iti3 


tmic  alcohols: 
c  acid  to  ethyl 


I*  in  the  alco- 

I.    The  lowest 

icid  reactions. 

the  acids  are 

in  the  animal 


ring  at  0°,  and 
extracted  from 


It  141°  0.     It 
rhen  ferment- 


Aer,  soluble  in 
the'  large  in- 


iter,  and  more 

In  f atfy  de- 

.  result  of  the 

I  the  urine  in 


Oapr«l0  add.     C.H...CO.H. 

Oaprylie  add.    CtH.».€X).H. 

Oaprte  Mid.       C.H...CO.H. 

These  acids  enter  into  the  fats  of  butter,  from  which  they  are  readily 
prepared.  They  are  all  mluble  to  but  a  slight  extent  in  water,  but 
readily  in  aloohol  and  ether.  They  probably  occur  in  the  products  of 
the  sebaceous  glands  and  the  sweat,  at  least  occasionally  in  some  ani- 
mals. 

Lftuoataaiie  add.   CiiHii.CX)tH. 

Xjriitie  add.         C»H,i.CO.H. 

They  occur  as  neutral  fats  in  butter,  spermaceti,  etc. 

Palaitkadd.   C..H...OO.H. 

Staadfl  add.      C.tH...CO.H. 

These  are  colorless  solids  with  melting-points,  the  former  at  (ISP  0., 
the  latter  at  eQ-g"  C.  Insoluble  in  water,  but  readily  dissolved  by  hot 
alcohol,  ether,  or  chloroform.  With  alkalies  they  form  soaps;  and  with 
glycerin  they,  together  with  the  oleates,  make  up  the  greater  part  of 
human  fat.  As  salts  of  sodium  (?)  they  occur  in  chyle,  blood,  serous 
fluids.  Combined  with  calcium  they  occur  in  the  faeces  and  the  adipo- 
oere  of  the  buried  cadaver.  They  are  said  to  occur  .^  in  the  caseous 
nodules  of  tubercle  and  in  decomposing  pus. 

The  Oleic  (Aerylie)  Acid  Seriee, 

General  formula  of  series  C,H»_,0^  Several  of  the  acids  of  this 
series  occur  as  compounds  of  glycerin  in  various  fats.  They  may  be 
decomposed  into  acids  of  the  acetic  series. 

Oleie  add.    C..H».Ot. 

The  most  important  to  the  physiologist;  is  a  colorless,  oily  liquid 
solidifying  to  a  crystalline  mass  at  4°  C.  Soluble  in  alcohol  and  ether 
but  not  in  water  ;  forms  soaps  with  alkalies. 

The  Neutral  Fata. 

To  understand  this  class  of  bodies  it  becomes  necessary  to  bear  in 
mind  the  relations  of  the  acids  of  the  fatty  and  oleic  series  to  glycerin. 
Olycerin  may  be  r^farded  as  a  tri-acid  alcohol: 

,  O.CO.Ci.H.1 

.CO.C..H..  +  3H.0. 


( OH     HO.OC.CiiH.. 
CtH.  ^  OH  +  HO.OC.Ci.H..  =  C.H. 


(OH 

Qlrowin. 


HO.OC.C..H,. 

Psbnlticacid. 


10.( 
^0.( 


.corcitH.1 

Qlyoerin  tri-iwliiiitate  or  palinltln. 


From  which  the  relations  of  glycerin  and  a  fatty  acid  to  the  neutral  fat 
appear— i.  e.,  a  neutral  fat  is  the  result  of  the  replacement  of  the  ex- 
changeable atoms  of  hydrogen  in  the  tri-atomic  alcohol  (glycerin)  by 
the  acid  radicles  of  the  acetic  or  oleic  series ;  so  that  the  neutral  fats  may 
be  regarded  as  ethers,  of  which,  in  the  nature  of  the  case,  there  are  theo- 
retically three  ;  but  those  only  in  which  the  most  complete  substitution 
has  taken  place  are  of  importance  from  a  physiological  point  of  view. 


,-t 

1 


% 


«8a 


ANIMAL  PHYSIOLOGY. 


These  neutral  fate  are  inaoluble  in  water  and  cold  alcohol,  soluble  in  hot 
alcohol,  ether,  chloroform,  etc. 

By  the  action  of  caustic  alkalies  or  superheated  steam  they  may  be 
readily  decomposed  into  glycerin  and  their  fatty  acids. 

Saponification  may  be  thus  represented  : 

( O.OC.CH,, 
CH.  \  O.OC.CH..  +  3KOH  =  CtH.(OH).  +  8CuH...C0.K. 
(  0.0C.C..H,. 

Palmittu.  •     Oljroerln.        PotMBium  pklmiUta. 

It  is  known  that  fats  are  not  only  emulsified  in  the  alimentary  tract, 
but  split  up  into  their  component  fatty  acids  and  glycerin.  A  certain 
proportion  of  soluble  soaps  are  formed  and  taken  into  the  blood ;  some 
insoluble  soaps  appear  in  the  faeces. 

But  the  chemical  changes  of  fats,  destructive  and  constructive,  effect- 
ed by  the  organs  that  prepare  food  to  become  blood,  are  doubtless  very 
complex,  and  in  large  part  as  yet  unknown. 

Olycdlio  Aeid  Serie: 

Glycol  may  be  formulated  thus  :  jU,*^„.  *«  general  formula  of  the 

glycols  being  CH^^^iOr— i-  e.,  the  glycols  are  diatomic  alcohols,  from 
which  acids  may  be  obtained  by  oxidation,  thus  : 

CHtOH     ^      C0.H        _^ 

6h.oh  +  ^  =  ch.oh  +  °'^- 

Glycol.  GlycoUc  add. 

By  additional  oxidation  a  member  of  the  glycolic  series  may  be  con- 
verted into  one  of  the  oxalic  series,  thus  : 

^=^  +  0.  =  (CO.H).+  H.O. 

Olyoollc  acid.  Ozalio  add. 

/OH 

1.  iMtie  Mid.  C.H«Oi  or  CtH«^(^g. 

Exists  in  four  isomeric  conditions,  threeof  which  have  been  found  in 
the  mamnudian  (hujum)  body.  The»  have  the  following  properties  in 
common :  Are  sirup-like  in  consistence,  colorless,  soluble  in  water,  alco- 
hol, and  ether  ;  have  an  extremely  sour  taste  and  a  strong  acid  reaction. 
They  form  salts  Oactates)  with  the  metals,    (a)  Ordinary  kustie  acid,  in 

active  ethylidene-lactic  acid,  a  hydroxyl-propionic  add,  OH».CH^QQ*g 

This  is  the  form  of  lactic  acid  that  occurs  in  the  fermentation  of  milk. 
It  is  found  in  the  contents  of  the  stomach,  intestines,  and  pathologically 
in  the  urine,  (b)  Ethyhne-laetie  aeid.  This  isomer  of  lactic  acid 
occurs,  though  there  is  some  doubt  about  the  subject,  in  muacle.    (c) 

Saredlactie  aeid,  active  ethylidene-lactic  acid,  CU,.CR^qq^.    This 

acid  may  be  readily  obtained  from  flesh,  and  is  therefore  found  in  abun- 
dance in  the  "meat  extracts."    It  is  the  only  one  of  the  laotio  acids 


APPENDIX. 


683 


soluble  in  hot 
I  they  may  be 

...COtK. 

n  iwlmiuto. 
iinentary  tract, 
in.    A  certain 
e  blood ;  some 

LmctiTe,  effect- 
doubtleas  very 


formula  of  the 
alcohols,  from 


e«  may  be  con- 


e  been  found  in 
ig  properties  in 
)  in  water,  alco- 
g  acid  reaction. 
1/  lactic  acid,  in 

itation  of  milk. 
1  pathologically 
r  of  lactic  acid 
in  muscle,    (c) 

H/OH_  rpiji- 
NCO.H-  ^'"* 
found  in  abun- 
the  laotio  adds 


that  rotates  the  plane  of  polarised  light,  the  free  acid  being  dextro-ro- 
tatory. 

The  Bibane  Adda  (C.H*  -  .00  of  the  Oxalic  Seriee. 
Only  a  few  members  of  this  series  are  of  special  interest  to  the  medi- 
cal chemist. 

OulieMid.    C.H.O«,(CO.H).. 

Does  not  occur  free  in  the  mammalian  body,  but  is  normally  present 
in  small  quantity  as  an  oxalate,  chiefly  of  calcium,  in  the  urine  of  most 
mammals.  In  certain  disordered  states  of  the  metabolism  it  oeiswn  in 
the  urine  of  man  in  characteristic  dumb-bell  forms,  in  regular  octahedra, 
or  in  square  columns  with  pyramidal  ends.  These  are  insoluble  in 
water,  alcohol,  ether,  ammonia,  and  acetic  acid,  but  readily  dissolve  in 
hydrochloric  acid. 

SoMdikie  add.    C.H4(CX).H)t. 

Occurs  in  the  spleen,  thymus  and  thyroid  bodies,  and  in  hydrocele 
and  hydrocephalic  fluids.  It  crystallizes  in  large  rhombic  tablets,  and 
more  rarely  in  prisms;  sparingly  soluble  in  water. 

CoMPLBZ  NiTRoaKtrous  Fats. 

The  bodies  to  be  described  in  this  chapter  may  most  of  them  be  ex- 
tracted from  the  nerves  and  nervous  centers, 

iMithin.    C«.H..NPO..  ' 

This  substance  may  be  obtained  from  diverse  sources — the  blood,  bile, 
serous  fluids,  and  especially  from  the  brain,  neiives,  yelk  of  egg,  semen, 
pus,  the  colorless  corpuscles,  and  even  the  eltxstrical  organ  of  fishes.  It 
may  be  separated  as  a  white,  somewhat  crystalline,  soft  body,  soluble  in 
cold  alcohol,  more  so  in  hot  alcohol,  in  ether,  chloroform,  fats,  benzol, 
etc. 

Olyonliiphotpliorte  add.    OfH*PO«. 

May  arise  as  a  decomposition  product  of  lecithin,  thus: 

C44H.«NPO.  +  SHtO  =  2Ci*Hi.0<  +  C.H.PO.  +  C»HuNOi. 

Lecithin.  Stoarioaoid.     Ofyoerinpho*-         Neurin. 

pboric  acid. 

Protagoa.    CimHi..N.PO..  (?). 

The  formula  of  most  of  these  bodies  is  doubtful,  and  especially  is  this 
remark  true  of  protagon.  This  body  is  insoluble  in  cold  water,  but 
swella  in  it  like  gelatin.  At  200"  C.  it  melts  fo  a  sirup.  There  has 
been  much  discussion  as  to  whether  it  is  a  single  body,  or  a  mixture  of 
lecithin  and  cerebrin.    It  is  derivable  from  the  brains  of  mammals. 

Venxin.    CHuNOt. 

It  ia  a  very  unstable  body,  difficult  to  get  or  keep  in  a  free  state.  It 
haa  been  obtained  from  bile;  hence  the  name  cholin. 

CSamlttiii.    CitHnNOi  (t). 

Abounds  in  the  brain  in  the  axis  cylinder  of  nerves  and  in  pus-oor- 
pttsdes.    It  may  be  obtainecl  as  a  colorless  hygroscopic  powder. 


•^iHlliMMHIill 


laiMMili 


mmmtm 


684 


ANIMAL  PHYSIOLOGY. 
The  Sbbies  of  Bilb  Acids,  etc. 


Cholio  (cholalic)  add.    Ct«H4tOi. 

It  is  the  starting-point  of  the  bile-acid  series,  and  may  be  obtained 
pure  in  an  amorphous  or  crystalline  form,  soluble  in  water.  This  acid 
is  dextro-rotatory.  It  may  occur  in  the  large  or  small  intestine  and  in 
the  fseces.  In  jaundice  it  is  in  excess  in  the  blood,  tissues,  and  excre- 
tions, especially  the  urine. 

Pettenkofer's  Teat.— With  sugar  and  sulphuric  acid  it  gives  a  red- 
dish color,  which  may  or  may  not  require  slight  heat  for  its  production ; 
but  it  is  important  to  remember  that  this  reaction  may  be  produced  by 
other  substances,  so  that  the  test  is  at  best  by  itself  a  doubtful  one. 

OlyooehoUo  add.    CmHmNO.. 

This  is  the  principal  acid  of  ox-gall ;  occurs  also  in  that  of  man,  but 
apparently  not  in  the  bile  of  camivora. 

This  acid  crystallizes  in  fine  needles,  soluble  in  water  especially  if 
hot,  in  alcohol,  but  not  in  ether.    It  has  a  strongly  acid  reaction. 
C.«H4oO.     f    C.NH,0.    -    H.0    =    C«H4.N0.. 

Cholalic  acid.  Qljrcin.  Glycocholic  acid. 

Whether  it  is  formed  in  the  body  in  the  manner  indicated  by  the 
above  equation  is  uncertain,  as  glycin  has  not  as  yet  been  obtained  free 
from  any  tissue.    This  acid  is  best  prepared  from  ox-gall. 

Tavroeholio  add.    C..H..NSOt. 

Though  found  in  ox-gall  it  is  most  plentiful  in  human  bile,  that  of  the 
camivora,  and  especially  in  dog's  gall.  .      ,  ^,    .         .         j 

It  crystallizes  in  needles  but  not  readUy.  It  is  soluble  in  water  and 
alcohol,  insoluble  in  ether.  Its  salta  are  also  soluble  in  water.  Tauro- 
cholic  acid  is  a  very  insoluble  substance. 

C..H4.NO7S  =  Ct4H4.0. -J- C.H,N0.8  -  H.O. 

Taurocholic  acid.    ChdaJic  acid.  Taurin. 

Like  the  preceding,  it  is  dextro-rotatory. 

Chokitariii.    Ct.H41.OH.  .    .^  ^  .  ^ 

Remarkable  as  the  only  free  alcohol  occurring  in  the  human  body. 
This  substance  may  readily  and  in  great  abundance  be  extracted  from 
the  nervous  tissues,  but  most  easily  from  gall-stones,  of  which  it  forms  a 
large  part  It  can  be  derived  from  other  tissues,  the  blood  and  especial- 
ly bUe.  It  may  be  obtained  in  white  fine  needles  from  solution  m  hot 
alcohol,  ether,  etc.    The  substance  is  tevo-rotatory.  ^  ^    ,  , 

Test  -Strong  sulphuric  acid  added  to  it  in  solid  form  and  heated,  or 
to  its  solution  in  chloroform,  gives  a  bright-red  color,  which  changes  on 

standing. 

Bile-Pigments. 

BOirabin.    C..H,.N.O..  ^  ^„  \..v         «    -. 

It  makes  up  a  great  part  of  the  pigment  of  the  bile  of  the  carnivora 
and  perhaps  of  man.  It  abounds  also  in  gall-stones,  from  which  it  may 
be  obtained,  in  either  the  amorphous  or  crystalline  condition,  by  extiwct- 
ing  with  chloroform  and  further  treatment    When  heated  with  mtrous 


APPENDIX. 


685 


lay  be  obtained 
iter.  This  acid 
Qtestine  and  in 
lues,  and  excre- 

it  gives  a  red- 
its  production ; 
l)e  produced  by 
litful  one. 

lat  of  man,  but 

er  especially  if 
reaction. 

•NOt. 

dUc  acid. 

idicated  by  the 
m  obtained  free 


bile,  that  of  the 

>le  in  water  and 
.  water.    Tauro- 

.0. 


le  human  body. 
)  extracted  from 
which  it  forms  a 
tod  and  especial- 
.  solution  in  hot 

n  and  heated,  or 
hich  changes  on 


of  the  camiTora 
>m  which  it  may 
lition,  by  extract- 
tted  with  nitrous 


acid  it  undergoes  a  series  of  oxidations,  giving  rise  to  distinct  products 
of  which  one  is  the  green  biliverdin.  These  oxidations  are  the  basis  of 
QmdM»  test  for  bile-pigment,  which  consists  in  adding  a  drop  of  strong 
nitric  acid  containing  nitrous  acid  to  bile,  when  a  series  of  rather  rapid 
changes  in  color  in  a  certain  order  takes  place. 

BiliTtrdin.    C»Hi.N.04. 

It  is  this  pigment  which  gives  the  characteristic  color  to  ox-gall,  from 
which  it  is  best  prepared.  It  is  not  soluble  in  ether  or  chloroform,  but 
dissolves  readily  in  alcohoL 

In  all  probability  both  the  bile-pigmente  and  their  derivatives  are 
the  result  of  the  final  transformations  of  haemoglobin. 

Chdtteliii.    CuH..N.O*. 

This  is  the  final  product  of  the  oxidation  of  bilirubin. 

Hydrobilirnbin.    CnHulftO,. 

When  an  alkaline  solution  of  bilirubin  is  acted  upon  by  sodium  amal- 
gam, the  above  results.  It  is  thought  by  many  to  be  identical  with  ster- 
cobilin,  a  product  of  the  decomposition,  etc. ,  of  bile  in  the  intestine.  Since 
hydrogen  in  the  nascent  condition  probably  occurs  in  the  intestines  as 
the  result  of  fermentations,  the  conditions  for  the  formation  of  this  sub- 
stance seem  to  be  met. 

Pigmentg  of  Urine, 

It  seems  to  bo  more  than  probable  that  the  urine  contains  a  great 
number  of  pigments.    But  few  of  these,  however,  have  been  isolated. 
The  best  known  are  the  following: 

XTrobilin.    C.iH«.N«0.. 

The  formulae  of  all  these  bodies  are  but  indifferently  known. 

Urobilin  is  thought  to  be  identical  with  hydrobilirnbin.  It  is  pres- 
ent, but  in  small  quantities,  in  normal  urine,  though  often  largely  in  the 
urine  of  febrile  conditions.  It  is  supposed  to  be  an  oxidized  form  of 
chromogen. 

ITroerythrin. 

Supposed  to  abound  in  the  urine  of  rheumatic  patients.  It  becomes 
greenish  on  addition  of  caustic  alkali,  and  reddish  or  reddish-yellow  when 
concentrated  hydrochloric  acid  is  added. 

The  Indigo  Series. 

Indioui.    CmHiiNOii. 

Some  regard  indican  as  indoxyl  sulphuric  acid,  which  does  not  occur 
in  the  free  state,  but  as  a  salt  of  potassium.  It  represents  in  the  urine 
the  indol  of  the  alimentary  canal. 

Indigo.    C>«HitN«Ot. 

It  occasionally  occurs  in  sweat  and  urine  as  an  oxidation  product  of 
indican. 

It  may  be  obtained  from  human  urine,  and  still  more  readily  from 
that  of  Uie  herbivora,  by  the  cautious  addition  of  a  weak  solution  of 


■^'»i/.i-7,*i>i:Jf'^\ii:r.: 


f.  iitf»^^^^'^~y'. 


686 


ANIMAL  PHYSIOLOGY. 


chlorinated  lime  to  some  urine  to  vrhich  an  equal  bulk  of  strong  hydro- 
chloric acid  has  been  added.  Unless  gfreat  care  is  employed  in  mixing 
up  the  fluids,  in  the  drop-by-drop  addition  of  the  solution  of  chlorinated 
lime,  the  indigo-blue  will  be  oxidized  (bleached)  to  indigo-white. 

"riie  substance  is  soluble  in  chloroform  which,  being  heavy,  falls  to 
the  bottom  of  the  glass  and  carries  with  it  the  indigo. 

IndoL    CHtN. 

A  substance  to  which  the  odor  of  fasces  is  in  part  due.    It  occurs  in 
artificial  and  natural  pancreatic  digestion  as  a  product  of  the  action  of 
bacteria.    It  is  crystalline,  soluble  in  boiling  water,  alcohol,  and  ether. 
Its  alcoholic  solution  when  nitrous  acid  is  added  gives  a  red  color  and  j 
its  aqueous  solution  a  red  precipitate. 

SkatdL    C.H.N(?). 

A  substance  occurring  under  the  same  circumstances  as  indol.  It 
does  not  give  the  same  reactions  with  nitrous  acid  as  indol,  but  gives  a 
violet-red  color,  when  in  urine,  on  the  aidd'tion  of  concentrated  hydro- 
chloric acid.  It  may,  like  the  preceding,  be  obtained  in  crystalline 
form. 

NrntoaBNOus  Metaboutis. 

As  may  be  gathered  by  a  perusal  of  the  chaptbr  oh  the  metabolism 
of  the  body,  the  nitrogenous  metabolism,  while  most  interesting  and 
important,  presents  problems  which  as  yet  are  in  great. part  unsolved. 
However,  something  more  of  the  nature  of  certain  nitrogenous  chemical 
compounds,  either  occurring  in  the  body  or  related  to  such  as  are  pw  serj, 
may  now  be  considered  with  advantage. 


Vreft.    CO 


,/NH, 
nNH» 


Urea  may  be  regarded  as  the'  most  important  and  by  far  the  most 
abxmdant  solid  of  the  urine  of  man  and  many  other  mammals,  includ- 
ing practically,  so  far  as  known,  all  the  camivora  and  several  other 
groups.  It  also  occurs  to  a  slight  extent  in  the  urine  of  birds.  It  is 
found  in  small  quantity  in  blood  and  many  of  the  fluids  of  the  mam- 
malian body,  though  not  at  all  or  to  but  the  smallest  extent  in  muscles. 
It  may  be  prepared  from  urine  and  obtained  in  colorless  needles,  soluble 
in  water  and  alcohol,  but  not  in  anhydrous  ether.  When  urine  decom- 
poses, urea,  possibly  \mder  the  action  of  a  ferment,  becomes  ammonium 


carbonate: 


CO(g|;  -I-  H.0  =  (NH.).CO.. 


Urea  may  be  made  in  the  laboratory  in  several  ways,  some  of  which  are 
indicated  in  the  following  equations: 
1.  By  heating  ammonium  carbonate: 


^"\ONH*  - 


CON.H.  +  H,0. 


S.  By  heating  ethyl  carbonate  with  ammonia: 

CO(gg;|;  +  2Nfl.  =  CON.H«  +  2C.H.0. 


APPENDIX. 


687 


f  strong  hydro- 
oyed  in  mixing 
of  chlorinated 
>-white. 
'  heavy,  falls  to 


e.  It  occurs  in 
of  the  action  of 
Dhol,  and  ether, 
a  red  color  and 


«8  as  indol.  It 
idol,  but  gives  a 
entrated  hydro- 
1  in  crystalline 


the  metabolism 
interesting  and 
part  unsolved, 
^nous  chemical 
h  as  are  prrseiii 


by  far  the  most 
ammals,  includ- 
id  several  other 
)  of  birds.  It  is 
ids  of  the  mam- 
tent  in  muscles. 
I  needles,  soluble 
len  urine  deoom- 
>mes  ammonium 


me  of  which  are 


). 


3.  By  addition  of  water  to  cyan-amide: 

CN.NH. -H  H.0  =  CON.H4. 

4.  By  evaporation  of  ammonium  cyanate  in  aqueous  solution : 

CN(ONH.)  =  CON,H«. 
The  last  reaction  possesses  a  historical  interest,  for  it  was  by  tiiis 
method  that  an  organic  compound  occurring  in  the  animal  body  was 
first  formed  from  inorganic  substances  in  the  laboratory  by  Wohler  in 
1828.  Urea  forms  compounds  with  acids,  the  most  interesting  of  which 
to  the  student  of  animal  chemistry  is  the  following: 

^Vrea  nitrate.    CH4N.0.HN0t. 

When  urine  is  concentrated,  and  strong  nitric  acid  added  cautiously, 
the  above  crystallizes  out  in  glistening  six-sided  or  rhombic  tablets,  solu- 
ble in  water,  but  insoluble  in  ether.  This  makes  a  reliable  and  fairly 
delicate  test  for  the  presence  of  urea. 

ITricaeid.    C»H«N40.. 

This  metabolite  occurs  in  the  spleen  and  several  other  organs  and 
tissues;  sparingly  in  the  urine  of  noan  and  most  mammals;  abundantly 
in  that  of  birds  and  serpents,  in  which  it  takes  the  place  of  urea.  In  its 
purest  form  it  presents  itself  as  a  colorless  crystalline  powder,  tasteless 
and  odorless.  Its  crystalline  forms,  arising  spontaneously  from  urine, 
are  very  variable  and  always  colored.  Very  insoluble  in  cold  water, 
ether,  and  alcohol ;  readily  soluble  in  sulphuric  acid,  caustic  alkalies, 
and  some  of  their  salts.  The  most  important  salts  of  uric  acid  are  the 
urates  of  sodium,  potassium,  and  ammonium,  all  of  which  occur  in  urin- 
ary sediments. 

The  mureaeid  teat  for  uric  acid  is  as  follows:  Add  strong  nitric  acid 
in  very  small  quantity,  and  evaporate  to  dryness,  when  a  red  color 
should  appear,  which  on  addition  of  ammonia  gr.ves  rise  to  a  purple. 
The  following  equations  will  show  the  relations  oi  uric  acid  to  urea,  etc., 
so  far  as  laboratory  reactions  are  concerned.  We  have  in  the  body  of 
the  work  shown  that  uric  acid  is  not  in  all  probability  itself  an  anteced- 
ent of  urea  in  the  body: 

C.H4N4O.  +  H,0 -f  O  =  C«H,N.O« -t- CN.H«0. 

Urioaoid.  AUozmi.  Urea. 

C4N,H.0«  +  2H.O  =  CHtOt  +  0N,H40. 

Alloxan.  HeBozaUc  ticid.      Urea. 

CtH4N40.  -I-  H.0  -I-  O  =  C«H.N40i  -I-  CO.. 

Uric  acid.  Allantoin. 

C4H.N«0.  +  H,0  =  CH4N.O  -I-  C.H4N,0. 

Allantoin.  Urea.         AUanturic  acid. 

Uric  acid  has  been  made  artificially  by  fusing  together  urea  and  glyoo- 
cin  (glycin,  glycocoll,  or  amido4oetic  acid) : 

OiMtin.    C4H*NiOi. 

This  body  may  be  abstracted  from  dead  muscle,  and  obtained  either 
in  a  white  amorphous  condition  or  in  rhombic  prisms,  soluble  in  cold 


688 


ANIMAL  PHYSIOLOGY. 


water  and  in  ether;  less  so  in  alcohol.    Creatin  maybe  changed  into 
urea  and  sarcosin  or  methyl-glycin : 

C.H.N,Oi  +  H.0  =  C.H,NO.  +  CON.H4. 

Creatin.  Barcorin.  Unsa. 

It  may  also  be  formed  synthetically  under  the  action  of  acids.    Creatin 
may  by  dehydration  be  transformed  into  creatinin. 

Cieatiiiin.    CiHiNiO. 

This  body  may  be  regarded  as  dehydrated  creatin.  It  occurs  nor- 
mally in  fleah  and  urine,  and  may  be  obtained  in  prisms;  soluble  in 
water  and  alcohol,  but  not  appreciably  in  ether.  It  acts  as  a  strong 
base,  the  most  important  salt  being  the  zinc  chloride  (C«HtNtO)iZnCli.  • 

AUutoin.    C4H.N.O..  ,..       ^    1..  V 

A  body  characteristic  of  the  allantoic  fluid  of  foetal  life,  and  which 

may  occur  in  tiie  urine.    Its  relations  to  uric  acid  and  urea  have  been 

indicated  above. 

Eyposaatllill  (sarkin).    CiHiNtO. 

Occurs  in  flesh,  in  the  spleen,  liver,  medulla  of  the  bones,  etc.  It 
may  be  obtained  in  One  needles,  soluble  in  hot  water. 

Xuthin.    C.H.N«0.. 

May  be  derived  from  muscles,  the  liver,  spleen,  thymus,  and  some 
other  organs  and  tissues.  It  is  probably  a  normal  constituent  of  the 
urine  in  minute  quantity.  It  may  be  obtained  as  a  colorless  powder, 
only  slightly  soluble  in  water,  but  soluble  in  dilute  acids  and  alkalies. 
Xanthin  may  be  regarded  as  the  oxidized  form  of  hypoxanthin. 

Oumiii.    CtH.N40t.  ,    .     ,  ui 

Occurs  in  extinct  of  flesh,  and  may  be  obtained  in  crystals,  insoluble 

in  alcohol  and  ether,  but  slightly  soluble  in  cold  water,  and  more  so  in 

hut  water. 

GKuiiin.    CiH«N»0.  ^   *  v  j  \    •* 

So  called  because  first  obtained  from  guano  (excrement  of  buds);  it 

is.  however,  also  to  be  extracted  from  several  organs  and  tissues;  as  a 

white  amorphous  powder,  insoluble  in  water,  alcohol,  ether,  etc.    By 

treatment  with  nitrous  acid  it  may  be  converted  mto  xanthin. 

Kymreiiit  add.    CmHkNiOi. 

This  body  has  been  found  in  the  urine  of  dogs. 

Qlydli.      (Glycocoll,  glycocin,  amido-acetic  acid.)      CiH.NOt,  or 

«TT  /NHt 
*^»nOO.H- 

This  is  one  of  that  important  class  of  compounds,  the  iunido-acid% 
and  may  be  formed  m  tiie  laboratory  from  mono^hlowicetio  acid  and 

ammonia: 

C.H,C10,  +  2(NH.)  -  C.H.(NH.)0(0H)  +  NH.a. 

It  is  peculiar  in  having  both  acid  and  basic  properties-i.  e.,  it  unites 
with  both  acids  and  bases  to  form  crystallimble  compounds.  Olyc™ 
itself  may  be  obtained  in  crystalline  form  soluble  in  water.    Though 


APPENDIX. 


689 


le  changed  into 


I  acids.    Creatin 


It  occurs  nor- 
isms;  soluble  in 
acts  as  a  strong 
,H,N.O).Znai. 

I  life,  and  which 
I  urea  have  been 


le  bones,  etc.    It 


lymus,  and  soine 
Dnstituent  of  the 
rolorless  powder, 
ids  and  alkalies, 
izanthin. 

irystals,  insoluble 
r,  and  more  so  in 


nentof  birds);  it 
and  tissues;  as  a 
1,  ether,  etc.  By 
an  thin. 


)      CiHiNOi,  or 


I,  the  amido-acids, 
lor^cetio  acid  and 

des— i.  e.,  it  unites 
mpounds.  Glyoin 
n  water.    Though 


C«HJf,0.,  or  C.H.(NH.);^J^*-i.  e., 


not  found  in  the  free  state  as  yet  in  the  body,  it  may  be  split  off  from 
bile  acids  and  hippuric  acid. 

Taflrin.    CHtNOiS,  or  C.H<|^^. 

This  is  an  amido-isethionic  acid,  and  may  be  made  artificially  by  a 
laboratory  synthesis,  as  well  as  derived  from  the  taurocholic  acid  of  the 
bile.  It  assumes  the  form  of  large  prisms,  soluble  in  water,  and  is  a 
remarkably  stable  compound.  Taurin  has  been  extracted  from  several 
organs  of  the  mammalian  body. 

Lendn.  O.H..NOi  or  OH.,  CH..CH,CH..C5H(NH«).C0.H— i.  e..  an 
amido-caproic  acid. 

This  compound,  which  may  be  obtained  from  the  pancreas,  spleen, 
thymus,  and  thyroid  bodies,  the  liver,  etc.,  and  occurs  as  a  product  of 
natural  and  artificial  pancreatic  digestion,  and  in  the  urine  in  acute 
atrophy  of  the  liver,  in  thin  whitish,  glistening,  flat  crjrstals,  soluble  in 
water.  Leudn  is  one  of  the  chief  products  of  the  decomposition  of 
nitrogenous  (proteid)  matter. 

A^angin, 

AmidiMmodiuunie  add. 
Found  in  many  plants— as  asparagus,  licorice,  haets,  peas,  beau  ,  etc. 
—but  not  in  the  animal  body,  so  far  as  is  yet  known. 

AMgutio  add  (or  Amido-succinic  acid). 
C«H,NO«  orC.H.(NH.)(gg|g. 

Found,  like  the  preceding,  most  abundantiy  in  seeds,  but  said  also  to 
occur,  in  minute  quantity,  among  the  products  of  pancreatic  digestion. 

Olvtaminio  add.    aH.N04. 

Seems  to  occur,  under  similar  natural  conditions,  to  those  giving  rise 
to  the  preceding  compound.  It  has  not,  however,  as  yet  been  shown  to 
arise  in  tiie  digestive  processes  of  animals. 

Ojitin.    CHrNSOi. 

By  some  chemists  this  compound  is  believed  to  be  an  amido-add.  It 
appears  occasionally  in  the  urine,  but  is  chiefly  of  importance  as  making 
up  the  greater  part  of  certain  urinary  calculi  in  men,  dogs,  etc.  The 
body  is  crystalline  :  insoluble  in  water,  alcohol,  and  ether,  but  soluble 
in  ammonia,  other  alkali^  and  the  mineml  acids. 

Acids  of  the  Benzine  or  Aromatic  Seriea. 
Buuoieadd.    C.H».CO.H. 

The  add  itself  is  not  known  to  exist  in  the  body,  but  may  arise  in 
urine,  especially  that  of  the  herbivora,  from  fermentative  decomposi- 
tion : 

O.H.NO.  +  H,0  =  C,H.NO.  +  C,H.O.. 

HIppurioMrid.  Oljcin.         BenioioMid. 

Benzoic  acid  is  very  sparingly  scluble  in  water,  but  readily  dissolved 
by  alcohol  and  ether. 
44 


690 


ANIMAL  PHYSIOLOGY. 


Hippuio  add  (Bemoyl-Glycin,  or    Bensoyl-amido- acetic    Acid). 

This  acid  abounds  in  the  urine  of  the  herbivora,  being  derived,  proba- 
bly, from  some  benzoic  r«ddue  in  the  food  (hay).  It  occurs  m  only 
smaU  quantity  in  tiie  urine  of  man.  It  may  be  obtamed  m  pinsms,  solu- 
ble in  boiling  water  and  in  alcohol. 

Fhend  (Carbolic  acid).    C.H..OH. 

This  compound  occurs  under  the  same  circumstances  as  mdol  in  the 
alimentary  tract,  and  may  be  extascted  from  the  fseces  and  the  urme. 
SUghtiy  soluble  in  water,  it  readily  dissolves  in  alcohol  and  etiier. 

This  substance,  the  molecular  constitution  of  which  is  still  m  doubt, 
is  certainly  an  aromatic  body,  which  may  be  obtained  in  needles ;  solu- 
ble in  hot  water,  acids,  and  alkaUes,  but  insoluble  in  alcohol  and  etiier. 

Tyrosin  occurs  with  leucin  in  ttie  decomposition  of  protaids,  and 
abundantiy  in  tiie  natiind  and  artificial  digestion  of  tiie  proteids,  by 
teypsin.  A  substance  greatly  resembling  it  has  been  made  arbficudly,  in 
the  laboratory,  by  a  syntheos. 


I 


^ 


io-aoetio    Acid). 

ig  derived,  proba- 
t  occurs  in  only 
d  in  piHsms,  solu- 


} 


!e8  as  indol  in  ihe 
is  and  the  urine. 
1  and  ether. 

1  is  still  in  doubt, 
in  needles ;  solu- 
loohol  and  ether, 
of  protsids,  and 
f  the  proteids,  by 
tade  artificially,  in 


INDEX. 


Aberration,  chromstie,  578. 

spherical  of  the  lens,  572. 
Absorption  of  digested  food,  HI 

by  lymphatics,  841. 

l^  skin,  418. 
Accelerator  nerves  of  heart,  370. 
Accommodation  of  eye,  5<t5. 
^^ct  of  inspiration,  870. 
Acid  albumin,  678. 
Adds,  taitj  series,  080. 

acrylic  or  oleic  series,  681. 

glycolio  series,  682. 

oxalic  series,  688. 

bile  series,  684. 

benzine  or  aromatic  series,  680. 
Afferent  nerves,  482. 
Affections  of  retina,  482, 578. 
After-images,  680. 
y  Air,  entrance  to  and  exit  from  lungs,  860. 

quantity  respired,  878. 

inspired  and  expired,  comparison  of, 
881. 
Albumin,  native,  672. 

egg,  672. 

serum,  072. 

add,  678. 

alkali,  673. 
Allantoin,  688. 
Allantois,  75. 

Alteration  of  generations,  27. 
Amido-sttcdnamic  add,  960. 
Amnion,  74. 
Amoeba,  morphology  and  physiology  of, 

12,18. 
Amylolytio  action  of  saliva,  806. 
Amylopsin,  816. 
Anacrotic  pulse,  240. 
Annmia,  164. 


Animal  chemistry,  671. 

heat,  461. 

body,  27. 

kingdom,  classification  of,  88. 
Anode,  107. 

Anomalies  of  refraction,  574. 
Anterior  fasciculi,  488. 

radicular  zones,  488. 
Antero-median  columns,  488. 
Aphasia,  684 
Apnoea,  808. 
Appendix. 
Area  pelludda,  67. 

opaoa,  67. 
Arteries,  221. 
Asparagine,  680. 
Aspartic  acid,  680. 

Asphyxia,  respiration  and  circulation  in, 
404. 

pathological,  406. 
Astigmatism,  678. 
Auditory  ossicles,  607. 

impulses,  610. 

sensations,  615.' 

perceptions,  616. 

judgments,  616 

discriminations,  616. 
Auricles  of  heart,  218. 
Automatism,  214. 
Axis  cylinder  of  nerve,  106. 

Bacteria,  18. 

Bensoic  add,  680. 

Bile,  composition  of,  811. 

salts,  812. 

pigments,  812,  684. 

digestive  action  of,  818. 

comparative^  814 


**wirw:<wg««*»Mi^a«JwW*^ililttM6W*ifega^*^^a^^ 


692 


ANIMAIi  PHYSIOLOGY. 


1:^ 


BUe,  secretion  of,  828. 
Bilirubin,  684. 
Biliverdin,  685. 
Biology  general,  1. 
Blastoderm,  67. 
Blind-spot,  587. 
Blood,  147. 

comparstiTe,  148. 
Blood-cells,  size  of,  149. 

Tarietiea  of,  148. 

ratio  of  varieties  of,  160. 

history,  151. 

decline  and  death  of,  158. 
Blood,     morphological     elemunts 
148. 

cub?**^  composition  of,  154. 

quantity  and  distribution  of,  156. 

coagulation,  157. 

clinical  and  pathological.  168. 

summary  of  physiology  of,  165. 

supply,  influence  of,  200. 

circulation  of,  216-221. 

velocity  of,  224. 

pressure,  224-228. 

quantity  of,  275. 

arterial,  888. 

venous,  888. 

carbon  dioxide  in,  888. 

vessels,  origin  of,  97. 
Brain,  498. 

circulation  in,  625. 
Broca's  convolution,  625. 
Bronchial  tubes,  structure  of,  868. 
Bulbus  arteriosus,  99. 
Buidaoh,  columns  of,  488. 

Capillaries,  281. 
Carbohydrates.  140,  678. 
Cardiac  movements,  282. 

sounds,  285. 

cycle,  240. 
Camin,  688. 

Carbon  dioxide  in  blood,  889. 
Casein,  291,  678. 
Catelectrotonus,  197. 
Causes  of  heart-sounds,  286. 
Causation  of  heart-beat,  264. 
Caudate  nucleus,  586. 
Cell,  5. 
Cellulose,  7. 

Cerebro-cecebellar  fibers,  519. 
Cerebro-spinal  fibers,  610. 


of, 


Cerebral  cortex,  631. 

time,  585. 
Cerebro-spinal  and  system  of  nerves,  62(1. 

relations  of,  686. 
Cerebrum  general,  600. 

functions  of  its  convolutions,  606. 
Cerebellum,  functions  of  the,  641. 
Chemical  constitution  of  the  animal  bod^, 

186. 
Chemical  changes  in  muscle,  192. 
Cheyne-Stokes  respiration, '898. 
Chitin,  678. 

Chlorophyl,  11.  ' 

Choletelin,  686. 
Cholesterin,  684 
Ghondrin,  677. 
Chorion,  78. 

Chromatic  aberration,  578. 
Chronographs,  171. 
Chyle,  842. 

Cicatricula,  67.  r 

Cilia,  12. 
Ciliary  gimglion,  681. 

movements,  168. 
Ciroulation,  diagram  of,  224. 
under  the  microscope,  226. 
changes  in.  after  birth,  121. 
in  the  brain,  525. 
infiuenced  by  respiration,  400. 
Circulatory  and  respiratory  systemH,  man, 

664. 
Classification  of  animal  kingdom,  88. 
Classification  and  distinguiahing  charae 

tera  of  proteids,  188. 
Clinical  and  pathological,  blood,  188. 
re  nerve,  198. 
pulse,  251. 
saliva,  808. 
liver,  825. 
stomach.  886. 
vomiting,  889. 
lymph,  858. 
excretion,  864. 
digestion,  867. 
respiration,  879. 
asphyxia,  406. 
respiration,  406. 
glycogen,  485. 
fat,  445. 
heat,  467. 
vision,  602. 
hearing.  009. 


INDEX. 


698 


stem  of  nerves,  82(t. 


[Volutions,  SOS. 

1  of  the,  641. 

I  of  the  animal  bodjp, 

muscle,  198. 
fttion,'808. 


1,578. 


t  of ,  SM. 
ope,  886. 
>irth,  181. 

liration,  400. 
intoiy  systemtt,  man, 

mal  kingdom,  88. 

istinguishing  chatme 

,188. 

>gioal,  blood,  168. 


Clinical  and  Pathological,  taste,  035. 

spinal  nerves,  687. 

cranial  nerves,  689. 

voice,  646. 

speech,  651. 
Coagulation  of  the  blood,  157. 
Coitus,  181. 
Collateral  fibers,  510. 
Color-sensations,  588. 
Color-blindness,  586. 
Columns  of  TQrck,  488. 

Burdach,  489. 

Gall,  489. 
Commissural  fibers  in  brain,  518. 
Comparative  re  blood,  143. 

heart's  pulsations,  243. 

pulse,  861. 

circulation,  868. 

capillaries,  881. 

digestion,  896, 819, 867. 

teeth,  804. 

saliva,  80a 

bile,  814. 

stomach,  880. 

swallowing,  885. 

vomiting.  889. 

movements  of  lymi^,  848. 

respiration,  875. 

hemoglobin,  889. 

protective  f nnction  of  skin,  818. 

respiration  by  skin,  415. 

kidney,  419. 

urine,  486. 

fM,445. 

heat,  468. 

spinal  cord,  405. 

vision,  687. 

hearing,  616. 

smell,  688. 
.tMte,686. 

voice  and  speech,  647. 

locomotion,  660. 


Conjugation,  17. 

Oonstitution  of  animal  body,  187. 

Constitution,  chemical,  of  the  animai 

body,  186. 
Constituents  of  dead  muscle,  198. 
Contraction,  tetanic,  188. 

a  single  simple  muscular,  178. 

law  of,  19a 

of  pupil  (myosisV  671. 


Contrast,  687. 
Go-ordination,  490. 

of  the  two  eyes  in  vision,  691. 
Corpuscles,  composition  of,  155. 
Corpus  luteiini,  118. 

striatum,  functions  of,  686. 
Corpora  quadrigeiAhia,  functions  of,  589. 

striata,  518. 
Coughing,  406. 
Cranial  nerves,  68a 
Cramp,  806. 
Creatin,  197.  087. 
Creatinin,  446. 

Crura  cerebri,  functions  of,  541. 
Crusta,588. 
Crying,  406. 
Curve,  the  muscle,  180. 
Cystin,689. 

Death,  66a 
Decussation,  480. 
Defecation,  887. 
Deglutition,  880. 
Dentition,  666. 

Deyelopment,  physioloj^cal  aspects  of, 
118. 

post-embryonic,  of  blood-cells,  158. 
Dextrin,  679. 
Dextrose,  678. 
Diapedesis,  881. 
Diastole,  840. 
Diabetes,  artificial,  486. 
Dicrotic,  849. 

Dioidua  vera,  scrotina,  reflexa,  81. 
Diet,  468. 

tata  and  carbohydrates  in,  467. 

salts,  etc.,  in.  45a 

pathological,  450. 
Diffusion-circles  665. 
Differentiation  of  unicelluhir  animals,  80. 
Digestion  of  food,  890. 

comparative,  806,  819,  867. 

pathological,'B67. 

summary,  864. 
Digestive  juices,  806. 

action  of  bile,  818. 

organs,  self-digestion  of,  887. 
movements,  881. 
evolution,  308. 

system,  man,  664. 
Dilation  (mydriasis),  672. 
Dioptrics  of  visioUi  66a 


ANIMAL  PHYSIOLOGY. 


Direct  obiervation,  method  of,  141. 

oerebellw  tnots,  488. 
Discus  proligeriu,  58. 
Divisions  o£  food-stuffs,  aW. 
Dreaming,  627. 
Ductus  venosus,  104. 
Dyspnoea,  887. 

Ectoplasm,  7. 

Efferent  nerves,  482. 

Elasticity  of  muscle,  187. 

Blastin,677. 

Electrical  phenomena  of  moMle,  loo. 

organs,  199. 
Electrodes  non-polariaable,  189. 
Blectrotonus,  197. 
Embryo,  54. 

development  of,  90. 
Bmbryologioal,  alimentory  traot,  295. 
nerrooa  system,  542. 
virion,  502. 
Endoplasm,  7. 
End-plates,  nerve,  170. 
End-bulbs  of  Krause,  540. 
Energy  of  the  animal  body,  459. 
Entoptic  phenomena,  574. 
Epiblart,98. 
Estimation  of  the  slw  and  distance 

objects.  605. 
Eustachian  tnbe,  600. 
Evolution  of  vascular  system,  285. 
digestive  organs,  868. 
respiratory  organs,  400. 
uric  acid,  448. 
digestion,  468. 
spinal  cord,  496. 
nervous  system,  048. 
evidences  of,  48. 
placenta,  89. 

organic,  reconsidoced,  127. 
vision,  600. 
▼oioe  and  speech,  662. 
locomotion,  662. 
hearing,  616. 
Excretion  of  perspiration,  416. 
by  kidney,  419. 
pathological,  864 
Experimental,  reflex  action,  212. 
Expulsion  of  urine,  429. 
Extractives  of  muade,  194. 
Bye,  optical  imperfections  of,  572* 
protective  mechanisms,  696. 


PiBce8,858. 
Fallopian  tube,  114. 
Fatigue,  200. 
Fats,  the,  189. 
peculiar,  140. 
In  milk,  292. 
Pat,  the  construction  of,  440. 
formation  of,  441. 
pathological,  446. 
comparative,  445. 
Feeding  experiments,  454. 
Ferments,  unorganised,  160.  ^ 

Fibrin,  676. 
Fibrin-ferment,  160. 
Fibrinogen,  159,  674  , 

Fission,  11. 

FoBtal  circulation,  108-118. 
Food,  digestion  of,  290. 
,     special  considerations,  868. 
Food-stuffs,  divisions  of,  290. 
Forced  movements,  604 
Formic  acid,  680. 
Prog,  the  rheoscopio,  191. 
Fungi,  16. 

Ganglia,  cardiac,  278. 
Ganglion,  ciliary,  otic,  etc.,  «l. 
of    Gas-pump,  mercurial  (Ludwig^s),  »J4. 
Gases,  foreign  in  respiration,  892. 
Gastric  juice,  806. 

characters  of,  809. 
Oastmla,  the,  66. 
Gelatine,  677. 
Gelatine  in  diet,  467. 
Gemmation,  11. 
Germinal  vesicle,  54. 
spot,  64 
ridge,  57. 
Globin,  674 
i  Globulins,  674 
I  Glomerolas,  42. 
Glyoin,  688. 
Glycocholio  aoid,  812. 
Glyooooll  (glycln),  812-. 
Glycogen,  482, 679. 
uses  of,  484 
pathological,  485. 
Olutaminic  acid,  689. 
Goll,  columns  of,  ^9. 
GolU,  experiments  of,  628. 
Graafian  follicles,  57. 
Gray  matter  of  cerebrum,  512. 


INDEX. 


696 


of.4ML 


1.464. 
sed,160. 


08-118. 
890. 

ions,  858. 
M  of,  390. 
504. 

0,191. 


itic,  etc.,  681. 

ial  (Ludwig'8),  884. 

ispintion,  889. 


B5. 


its  of,  538. 
^67. 
etebmm,  512. 


Unphic  method,  applications  of,  171. 
Growth  St  different  periods,  6tt8.  j 

Guanin,  688. 

Habit,  the  law  of,  4a 
Hnmatoblasts.  149. 
Hsmatin,  889. 
Hninin,  889. 
Hnmoglobin,  885 

comparatire,  889. 
Hearing.  604.  ^ 

Heart,  the  mammalian,  317, 383. 

the  action  of,  338. 

impolco,  388. 

sounds,  eausea  of,  386b 

work,  341. 

nenrons  system  in  relation  to,  361. 

beat,  causation  of,  370. 

aooelerator,  nerves  of,  885. 
Heat,  animal.  461. 

comparative,  463. 

production  of,  465. 

pathological,  467. 
Heat-producing  power  of  foods,  460. 
Hermaphroditism,  35. 
Hibernation,  465,  470,  537. 
Hiooough,  407. 
Hipporio  add,  4^. 
Holoblaatio,  70. 
Homotothermer,  465. 
Horopter,  the,  694. 
HypluB,  15. 
Hypemoea,  897. 
Hydra,  33. 
Hydrobilimbin,  686. 
Hypnotism,  538. 
Hypoblast,  69, 98. 
Hypozanthin,  688. 

Imperftetions  of  visual  perceptions,  587. 

Impulse  of  the  heart.,  388. 

Impulses,  path  of,  in  spinal  cord,  481. 

Indioan,  686. 

Indigo  seriee,  685. 

Indol,  818, 686. 

Induotorinm,  Du  Bois-Reymond's,  176. 

Influence  of  pigment  of  macula  Intea, 

689. 
Infusoria,  83. 
Inhibition,  venous,  316. 

of  reflexes,  485. 
Inosit,  679. 


Interoerebral  fibers,  518. 

Internal  capsule,  586. 

Intestinal  movements,  887. 

Inspiration,  act  of,  870. 

Irradiation,  587. 

Irritability  of  muscle  and  nerve,  168. 

Juice,  gastric,  806. 

pancreatic,  815. 
Juices,  the  digestive,  806. 

characteristics  of,  807. 

KaryokinesiB,  6, 66. 
KataoroUo  pulse,  349.  .' 
Kathode,  197. 
Keratin,  67a 
Kidney,  excretion  by,  419. 

comparative,  419. 
Kymograph,  381. 
Kynurenic  acid,  688. 

Latent  period,  181. 
Lardacein,  677. 
Laughing,  406. 
Law  of  contraction,  196, 

rhythm,  300. 
Lecithin,  688. 
Lenticular  nucleus,  686, 
Leuoin,  816. 
Leuoooytes,  160» 
Liquor  amnii,  74 

sanguinis,  150. 
Liver,  metabolism  of,  490. 
Localisation,  in  cerebral  cortex,  638. 680. 
Locomotion,  665. 
Looomotor  ataxia.  490. 
Lymph,  843. 

movements  of.  comparative.  848. 
Lymphatics,  absorption  of  food  by.  841. 

Macula  lutea.  influence  of  pigment*  of, 

588. 
Malpigfaian  tubules.  431. 
Maltose,  679. 
Man  at  different  periods  of  his  existence. 

MB 

Man's  place  in  the  animal  kingdom,  86. 
Maturity  (puberty),  666. 
Mastication,  883. 
Maximal  stimulus.  185. 
Medulla  oblongata.  543. 
M«ia)fflNMJknDpapi,  606. 


696 


ANIMAL  PHYSIOLOGY. 


Membnuien,  embryonio,  of  birds.  72. 

foDtal  of  mammal,  76. 
Menstniation,  lltt. 
Heroblaatic,  70. 
Meaoblast,  98. 
Mesonephrofl,  100. 
Metanephroa,  100. 
MeUbolism,  the.  of  the  body,  481. 
of  the  liver,  482. 
of  the  apieen,  480. 
in  formation  of  urea,  urio  aoid,  hippu- 

rio  acid,  etc.,  440. 
proteid,  455. 

influence  of  nervooa  syttem  on,  471. 
summary  ot  470. 
Meta»>a,5. 
Methsmoglobin,  880. 
Micturition.  480. 

pathological,  480. 
Middle  ear,  muscles  of,  008. 
Millc,  pioteids  of,  291. 
fats,  292. 

sugar  of.  292,  679. 
salts,  292. 
Minimal  stimulus,  185. 
Misconceptions  as  to  comparative  size, 

etc.,  of  objects,  690. 
Moist  chamber,  170. 
Morphology,  definition  of,  1. 
Motor  area,  525.  . 

Moyements,  cardiac,  282. 
ciliary,  108. 
stomach,  885. 
intestinal,  887. 
digestive  organs,  881. 
ocular,  592. 
Mucin,  827,  077. 
Mucor  mucedo,  15. 
Muoigen,  827. 
MDllerian  duct,  108. 
Multicellular  organism,  22. 
Munk,  experiments  of,  524. 
Muscle,  167. 
irritability  of,  109. 
onrre,  180. 

changes  in,  during  contraction,  180. 
elasticity  of,  187. 
electrical  phenomena  of,  188. 
electrical  uurrents  in,  190. 
chemical  changes  in,  192: 
dead,  constituents  of,  194. 
thermal  changes  in  contracting,  195. 


Muscle,  unstriped,  204. 

comparative,  205. 
Muscles  of  respiration,  872. 

of  middle  ear,  OOH. 
Muscular  note,  184 

worlc.  199. 

sense,  557. 

energy,  sources  of,  401. 
Mydriasis,  572. 
Myosis,  571. 

Myograph,  pendulum,  179. 
Myosin,  198,  074 

Nerve-supply,  048. 

Nerves,  the  physiology  of,  197. 

clinical  and  pathological,  198. 

irritability  '>f,  109. 

afferent  and  efferent,  482. 

oerebro-spinal,  620. 

third,  fourth,  etc.,  628,  629. 
Nervous  system,  210. 

in  relation  to  the  heart,  261. 

relation  to  respiration,  898. 

man,  666. 
Nervous  supply,  muscles  of  mastication, 

882. 
Nervous  mechanism  in  the  sexual  act, 

124 
Neurin,  688. 
Neuralgia,  517. 
Neutral  fats,  681. 
Nitrogenous  metabolites,  140,  686. 

equilibrium,  450. 

fats,  complex,  088. 
Non-crystalline  bodies,  677. 
Non-crystalline  bodies,  certain,  188. 
Non-nitrogenous  metabolites,  141. 
Note,  the  muscular,  184 
Nucleus,  6. 
Nucleolus,  5. 
Nuclein,  678. 

Objects,  estimation  of  sice  and  distance, 

590. 
Observation,  direct  method  of,  141. 

graphic  method  of,  148. 

summary  of  methods  of,  147. 
Ocular  movements,  592. 
Old  age,  667. 
Oligemia.  104 
Oncograph,  488. 
Ofisperm,  the,  62. 


fl,  certain,  188, 
Mbolites,  141. 

184 


Dethod  of,  141 

,148. 

ids  ojt,  147. 


INDEX. 


697 


Optio  thkUmi,  S18. 

Optio  th«laniii!i.  functions  of,  S80. 

Optical  imperfectiuns  of  tlie  eye,  572. 

Oifanio  eTolution,  41. 

Organs,  electrical,  100. . 

Origin,  the,  of  the  germs  of  life,  41. 

Orary,  origin  of,  110. 

Orulation,  116. 

Ovum,  the,  54. 

origin  and  development  of,  57. 

changes  in,  50. 

fertilization  of,  62. 

nutrition  of,  115. 
Oxyhemoglobin,  880. 

Pacinian  corpuscles,  552. 

Pancreatic  juice,  815. 

I'hysiology  of  secretion,  828. 

Paraglobulin,  150,  674. 

Parthenogenesis,  58. 

Parturition,  120. 

Patellar  reflex,  494. 

Path  of  impulses  in  spinal  cord,  401. 

Peduncles  of  the  brain,  537. 

Pepnn,  811. 

Peptone,  810,  815. 

Peptones,  675. 

Perspiration,  excretion  of,  416. 

Pettenltofer's  test,  684. 

Phenol,  600. 

Physiology  of  secretion,  810. 

sweating,  417. 
Pigments  of  urine,  685. 
Placenta,  80. 

the  discoidal  and  meta-discoidal,  81. 

the  zonary,  diffuse,  polycotyledonary, 
86. 

evolution  of,  80. 
Poikilcthermer,  465. 
Pokur  cells  of  globules,  59. 
Polyps,  22. 
Pons  Varolii,  518. 

functions  ot  541. 
Prediorotio,  240. 
Pressure  sensations,  554 
Pressures,  endocardial,  288. 
Primitive  strealc,  71. 

groove,  71. 
Pro-amnion,  78. 
Production  of  heat,  465. 
Pronephros,  06. 
Pronucleus,  female,  00. 


Protagon,  688. 

Protective  mechanism  of  the  eye,  596. 
Proteid  metabolism,  455, 
Proteid^  671. 

properties  and  clitssiflcation  of  the,  673. 

general  characteristics  of,  188. 

classification  and  distinguishing  char- 
acters of,  188. 

of  milk,  201. 

metabolism,  455. 

tests  for,  672. 

coagulated,  675. 
Protococcus,  morphology  and  physiology 

of,  11, 12. 
Protoplasm,  2, 27. 
Protovertebm,  05. 
Psychological  aspects  of  vision,  686. 
Pulse,  the,  244 

venous,  251. 
Pupil,  alteratior?;  in  the  size  of  the,  660. 

Quantity  of  air  respired,  878.' 

lioctioi  time,  586.  '  , 

Redur-^  reaction  time,  68^. 
Refle.-  action,  21) 

functions  of  sp'     ^  cord,  484 

time,  486. 
Reflexes,  inhilition  of,  485. 
Ref  ■_>,  .  11,  anomalies  of,  F  .1. 
Rr  rulati  '<  of  temperature,  464 
Reijurgitation,  840. 
Reproduction,  60. 
Research  and  reasoning,  phyaiologicai, 

W. 
Respiratory  system,  865. 

sounds,  870. 
Respiration,  muscles  of,  872. 

types  of,  878. 

comparative,  875. 

pathological,  870. 

in  the  blood,  388. 

in  the  tissues,  802. 

relation  of  nervous  system  to,  198. 

influence  of  oonditica  of  blood  in,  897. 

Cheyne-Stokes,  806. 

effects  of  variaMoas   in   atmo^teric 
pressure,  390. 

influence  on  circulation,  400. 

clinical  and  pathological,  408. 

evolution,  400. 
Resting  stage  of  ovum,  65. 


f 


698 


ANIMAL  PHYSIOLOGY. 


Rhythm,  law  of,  206. 
.'  -  in  nature,  86. 

appetite,  863. 

respiratory,  879. 
Retina,  affections  of,  S78. 
Retinid  stimulation,  laws  of,  580. 
Rigor  mortis,  192. 
Rheoscopic  frog,  191. 
Rouleaux  of  blood-cells,  158. 

Saliva,  806. 

amylolytic  action  of,  806. 

of  parotid  gland,  807. 

comparative,  806. 

pathological,  806. 
Salivary  glands,  physiology  of  secretion 

of,  819. 
Salte  of  milk,  292. 
Sarcolemma,  170. 
Secretion,  physiology  of,  819. 

nature  of  the  act  of,  826. 

of  urine,  426. 
Segmentation  of  ovum,  66. 
Segregation,  180. 

Self^digestion  of  digestive  organs,  829. 
Semicircular  canals,  co-ordinating',  func- 
tions of,  502. 
Sensation^  visual,  576. 
Senses,  general  remarks,  646. 
Sensory  area,  525. 
Serum,  composition  of,  156. 
Sexes  at  different  periods,  667. 
Sexu«l  selection,  42. 
Sighing,  407. 
Skatol,  686. 
Skin,  functions  of,  412. 

protective  functions  of,  oomparativc, 
418. 

laapiration  by,  comparative,  416. 

absorptlim  by,  418. 

as  an  organ  of  sense,  451. 
Sleep,  526. 
Smell,  sense  of,  620. 
Sneenng,  407. 
Sobbing,  406. 
SoUdity  in  vision,  595. 
Somatopleure,  74. 
Somnambulism,  529. 
Sound,  cardiac,  MArey's,  284. 
Sounds,  cardiac,  285. 

respiratory,  981. 
Special  considentioiu  as  to  food,  868. 


Special  considerations  as  to  digestion,  468. 

vision,  597. 

hearing,  616. 

voice  and  speech,  652. 
Spectrum  of  hsm^globin,  886. 
SpermatojioOn,  62. 

origin  of,  61. 
Speech,  6tt. 

consonants,  650. 
Spherical  aberration,  672. 
Sphygmograph,  the,  247. 
Spinal  nerves,  626. 

cord,  480.  i 

reflex  functions  of,  484. 
as  a  conductor  of  impulses,  487. 
automatic  functions  of,  498. 
comparative,  496. 
evolution,  496. 
Splanchnopleure,  74 
Sporangia,  16. 
Spleen,  metabolism  of,  486. 

nervous  system's  influence  on,  489. 

pulp,  comparative,  487. 
Stasis,  281. 

Starvation,  influence  on  metabolism,  460. 
Steapsin,  810. 

Stimulation,  laws  of  retinal,  681. 
Stimulus,  170. 

maximal,  186. 

minimal,  186. 

8ub-maximal,  186. 
Stomach  of  ruminants,  800. 
:  physiology  of  secretion  by,  828. 

comparative,  880. 

movements  of,  886. 
Subjective  phenomena,  691. 
Suoous  enterieus,  817. 
Summary  of  physiology  of  blood,  166. 

muscle  and  nerve,  208. 

oinulation,  286. 

digestion,  856-864. 

respiration,  410. 

fniwtions  of  the  skin,  413.  ' 

urine,  480. 

reproduction,  60. 

voice  and  speech,  668. 

spinal  cord,  497. 

functions  of  the  brain,  648. 

of  evidences  of  evolution,  47. 
Swallowing,  comparative,  884, 886. 
Sweating,  416. 

physiologj  of,  417. 


•*- 


INDEX. 


699 


as  to  digestion,  468. 


(2. 

bin,  386. 


573. 
47. 


1,484. 

impulses,  487. 
>iis  of,  498. 


,486. 

flaence  on,  480. 

487. 

}n  metabolism,  4G0. 

etinal,  681. 


8,800. 

;ion  hj,  888. 


t,  AOl. 

17  of  blood,  165. 
108. 


ii,4ia 


tin,  548. 
ution,  47. 
Ave,  884, 885. 


Synopsis,  brief,  of  physiology  of  vision, 
602. 
physiology  of  hearing,  620. 
Systole,  240. 

Tactile  sensibility,  556. 

Tambour  of  Marey,  177. 

Taste,  sense  of,  dSXS. 

Taurin,  812. 

Ttturocholio  acid,  812. 

Teeth,  comparatire,  804. 

Tegmentum,  688L 

Temperature,  influence  of,  oh  muscle,  202. 

regulation  of,  464. 
Testes,  61. 

Tests  for  proteids,  672. 
Tetanic  contraction,  188. 
Thermal  changes  in  contracting  muscle, 
195. 

sensations,  554. 
Thoracic  breathing,  878. 
Time,  cerebral,  586. 
Tissues,  the  contraotile,  IW. 

respiration  in,  892. 

oomparatiye,  167. 
Traube-Hering  curree,  408. 
Trypsin,  816. 
Tunicin,  680. 
TQrbk,  columns  of,  488. 
Types  of  respiration,  878. 
Tyrosin,  816. 

Unicellular  animals,  20. 
Umbilical  vesicle,  72. 
Urea,  4M,  686. 

and  uric  acid,  metabolism,  in  forma- 
tion of,  446. 

nitrate,  687. 
Urie  acid,  448. 

evolution,  448.  ^ 

Urine,  chemically  and  physiologically 
considered.  ^2. 

quantity,  428. 

constituents  of, 

salts  of,  424. 

abnormal,  425. 

oompuative,  43)6. 

secretion  of,  426. 

expulsion  of,  439. 

pigments  of,  685. 
UrobiUn,  686. 
Uroerythrin,  685. 


Urogenital  system,  development  of,  106. 
Uses  of  glycogen,  484. 

Vagus,  influence  on  the  heart,  266. 
Valves  of  the  heart,  219. 
Valvulaa  conniventes,  857. 
'Variations,  functional,  in  muscle,  207. 

of  cardiac  pulsation,  242. 
Vascular  system,  evolution  of  the,  285. 

development  of  the,  108. 
Vaso-motor  influences,  277. 
Vas  deferens,  origin  of,  110. 
Veins,  221. 

valves  of,  222. 
Velocity,  the,  of  the  blood,  224 

of  nervous  impulse,  measurement  of, 
181. 
Venous  pulse,  261. 
Ventricles,  of  the  heart,  218. 
\  ision,  569. 

embryological,  502. 

dioptrics  of,  568. 

psychological  agptat  oi,  588. 

synopsis  of  physiology  of,  602. 

astigmatic,  678. 

spherical  aberration  of,  572. 

chromatic  aberration  of,  578. 

entoptic  phenomena  of,  574. 

anomalies  of  refraction  of,  674. 

sensations  of,  676. 

affections  of  the  retina  in,  578. 

psychological  aspects  of,  686. 

oo-ordin&tion  of  the  two  eyes  in.  691. 

estimation  of  solidity  by,  695. 
Visual  sensations,  576. 

impulses,  nature  of,  580. 

angle,  SS2j 

-perceptions,  imperfections  of,  587. 
VitelUn,  674 
Vitelline  membrane,  65. 
Voice  and  speech,  689. 

registers  and  falsetto,  644 

pathological,  646. 

comparative,  647. 

•volution,  652. 

summary,  652. 
Vomiting,  comparative,  888, 889. 

pathological,  889. 

Wolfllan  duct,  08, 100. 

bodies,  100. 
Work,  muscular,  199. 

of  the  heart.  241. 


700 


ANIMAL  PHYSIOLOGY. 


Xuthin,  194 

Yawning,  407. 

Yeast,  morphology,  chemistry,  »nd  physi- 
ology of,  0, 10. 


Zona  radiata,  05. 
ZoSgloea,  18. 
Zygospore,  17. 
Zymogen,  388. 


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one  of  theirs  -dsrd  text-lmaks.  The  work  has  very  few  eqaals  and  no  saperior  fa  oar  hainage, 
and  ereiybody  iuMws  it."— gjausmaaalaw  Jfimf%. 

**  TIm  atadent  and  tlie  piactlttonar,  whose  sound  prsetiee  mast  be  based  on  an  intelllmnt  ath 
prsdatian  of  tte  prindplef  of  phyaloldKy,  will  h«retn  flad  all  saMeets  in  which  Ihsy  are  inter- 
ested Itelly  discassed  and  Ihoroaghfy  ehAomted."—CWiv*  eatf  CliniMl  ilMsrvf. 

"  We  need  only  mj  tlmt  in  ttiis  third  edition  the  work  bas  been  carsftilly  and  tlmoaiaiy  rs- 
Tised.  It  is  one  of  oar  stsndafd  text-hooka,  and  no  physHlso's  Hbiaiy  shonld  be  withant  R.  We 
treasnre  It  hinfaly,  shall  give  it  a  choice,  snajr,  scr  -troKluent  posttian  on  onr  shelf,  and  daem  oar- 
selves  Ibrtanate  to  powKss  this  elegant,  oompraasa.  iva,  and  aaihoritative  work."— ilr  irican  B(pt- 


THE    SOURCE   OF   MUSCULAR 

POWER.  Aigaments  and  Conclusions  drawn  from 
Observations  upon  the  Haman  Subject  under  Condi- 
tions of  Rest  and  of  Muscular  Exercise. 

By  AUSTIN  FLINT,  Jb.,  H.  D., 
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8TO,10Spp.    Cloth,  $1.00. 


01^  THE  PHYSIOLOGICAL  EFFECTS 

OP  SEVERE  AND  PROTRACTED  MUSCULAR 
EXERCISE.  With  Special  Reference  to  its  Influence 
upon  the  Excretion  of  Nitrogen. 

Bf  AUSTIN  FLINT,  Jt.,  M.  D., 
Prof eaor  of  PhgnbkigK  ia  «iw  BeUavne  Hoapltal  Medical  College,  New  Toik,  ttc,  eta 

8TO,9Ipp.    Ohith,|1.00. 


New  York :  D.  APPLETON  A  CO.,  1,  8,  ft  5  Bond  Street 


!t"g*yM»W>JW»rr 


HY8I0L- 

ENTS  AND 


StpUnAer,  1889. 


MEDICAL 


AVD 


Hoapltal  Medical  Cet 
edtcine,  etc 

>,  and  profiuely  iUui- 
HTood.    Cloth,  t«.00; 

lolofctoM  or  the  d«y<  ^ 
t-book  ap  totkepreteBt 
jkal  RtporUr  OtlMaM- 

t  it*  WMtmtkM*.  In  the 
Bttftee  the  nbole  teM  or 
HCe."— iWraUZoMK. 

m.  Hie  m«dled  profee- 
naHtta  tnr  adoptlnit  it  at 
aperioT  In  oar  UHvnage, 

«d  on  an  telelHgent  ap- 
In  which  thejr  are  Inter- 


Bltally  and  tbotoaiAiy  te- 
uMMhewlSontB.  We 
onr  abclf,  and  deem  oar- 
work."— Arfiean  Sp»- 


iCTJLAR 

18  drawn  from 
t  under  Condi- 


J,  New  York,  otft,  etc. 

EFFECTS 

MUSCULAR 
to  its  influeiice 

e,  New  Tork,  etc.,  «t& 
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owing  ito  AppHoa- 
'active  DiMaae  or 
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Thirty  Oases  and 

ealth  and  Disease. 


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ith  tlieir  Applica- 
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ioal   Inveitigation. 
ed  by  Hermfinn  M. 


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ueit  (if  Women  and 
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KRY  DISEASES. 
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in  connection  with 
be  two  pnblioations 


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title,  bv  Van  Buren 
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ng  Local  Treatment 

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MAUDSLEY  (HENRY).  Physiology  of  the  Mind.  Being  the  first  part  of  a 
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MAUDSLEY  (HENRY).  Pathology  of  the  Mind.  Third  edition.  ISmo.  Cloth, 
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MAUDSLEY  (HENRY).  Responsibility  in  Mental  Disease.  12ino.  Cloth, 
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•7 


